1. JOURNAL OF RAMAN SPECTROSCOPY
J. Raman Spectrosc. 2006; 37: 562–573
Published online 22 November 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jrs.1432
A new single grating spectrograph for ultraviolet
Raman scattering studies
Lutz Hecht,1∗ John Clarkson,1 Brian J. E. Smith2 and Roger Springett3
1
Department of Chemistry, Joseph Black Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, Scotland, UK
2
Spectroscopy Products Division, Renishaw plc, Old Town, Wotton-under-Edge, Gloucestershire GL12 7DH, England, UK
3
Dartmouth Medical School, Dartmouth College, HB 7786 Vail, Hanover NH 03755, USA
Received 11 April 2005; Accepted 28 August 2005
A state-of-the-art single grating spectrograph for Raman scattering studies within the deep ultraviolet
(DUV) region of the electromagnetic spectrum is discussed. It is based on a high throughput DUV
version of a single-stage monochromator originally designed for use in the visible spectral region. Its
key components are two identical, newly designed calcium fluoride camera lenses each consisting of
five different individual optical elements. The first of these lenses collimates the Raman scattered DUV
radiation entering the spectrometer through its entrance slit. The second lens focuses the collimated beam
of dispersed Raman scattered DUV radiation emerging from a high-resolution reflection grating onto a
charge coupled device (CCD) detector with enhanced DUV sensitivity. A novel high transmission edge
filter is used as a blocking device for a sufficient rejection of the Rayleigh line generating a relatively
sharp transmittance cutoff at a Stokes Raman wavenumber shift of about ∼450 cm−1
employing 257 nm
DUV excitation. Overall, this new spectrograph enables rapid collection of Stokes DUV Raman scattered
photons at f/2 wide apertures with sufficiently large signal-to-noise ratios (SNRs) in relatively short
acquisition times and with an effective spectral resolution of approximately ∼6 cm−1
. Backscattered
Raman spectra of the following chemicals are presented as typical results illustrating the excellent
performance characteristics of this new DUV spectrograph for a variety of experimental conditions within
different scattering scenarios and for a relatively wide range of commonly used sample preparation
techniques: neat cyclohexane, laboratory air, polycrystalline D-glucose, single crystal L-alanine and a dilute
aqueous solution of 2 -deoxyadenosine. Copyright  2005 John Wiley & Sons, Ltd.
KEYWORDS: DUV Raman spectroscopy; DUV CCD Raman spectrograph; backscattering arrangement; calibration; software;
resolution; signal-to-noise ratio; resonant Raman scattering
INTRODUCTION
Since the intracavity frequency-doubled argon ion gas laser,
based on the pioneering work by Asher and cowork-
ers, became commercially available,1
many more research
groups, especially in recent years, have adopted Raman
scattering, employing excitation in the deep ultravio-
let (DUV) region of the electromagnetic spectrum (at
wavelengths shorter than < 300 nm) as another valu-
able spectroscopic tool.2–18
This has contributed to the
widespread promotion and global popularization of this
rather specialized spectroscopic technique compared to
ŁCorrespondence to: Lutz Hecht, Department of Chemistry, Joseph
Black Building, University of Glasgow, University Avenue,
Glasgow G12 8QQ, Scotland, UK. E-mail: lutz@chem.gla.ac.uk
Contract/grant sponsor: Renishaw plc.
Contract/grant sponsor: Scottish Higher Education Funding
Council; Contract/grant number: RDG 115.
the early, virtually single-handed but vital efforts by a
few individual scientists.19–41
Nevertheless, despite this
wave of renewed and almost renaissance-like interest in
DUV Raman spectroscopy for predominantly biochemical
applications,42
only a limited number of researchers appear
to be involved in developing better DUV spectroscopic
equipment.5,7,43,44
Most research groups still use rather inef-
ficient low aperture triple, double or single spectrographs
suffering from relatively poor resolution characteristics and
inferior photon collection capabilities and radiation transmis-
sion properties.3,4,6,8–12,14–18
More specifically, on the basis of
the common assumption that, for the purpose of obtaining
reasonable quantitative estimates for comparable spectrom-
eter throughput values and with all other experimental
conditions being equal, the relative geometric etendu of two
monochromators under investigation is given by the squared
ratio of their individual f/numbers,45
a spectrograph with
Copyright  2005 John Wiley & Sons, Ltd.

2. DUV Single grating spectrograph 563
a f/2.0 aperture is approximately 20 times faster than a
f/9.0 spectrograph3,15
and ca 10 times faster than a f/6.3
spectrograph.6,11,44
Although the field of DUV Raman spectroscopy would
certainly benefit greatly from employing high throughput
spectrometers, it is perhaps a little surprising that appropri-
ate low f/number monochromators for use within the DUV
spectral region have neither been discussed in the literature to
date nor do they appear to be commercially available yet. We
have consequently decided to construct our own ad hoc large
aperture DUV spectrograph for future action as the central
component of a state-of-the-art Raman scattering instrument
for novel in situ spectroscopic studies of a wide range of
heterogeneously catalyzed reaction systems. The unconven-
tional design of this spectrograph has been inspired by
previously published DUV Raman studies in heterogeneous
catalysis16,17
employing a fluidized bed reactor16
and by
recent results in phenomenological Raman scattering theory
permitting the identification of fully optimized scattering
configurations within particular scattering regimes.46
The
discussion of the initial stages in the development process
of this fast single grating spectrograph customized for DUV
operation, predominantly associated with its configuration,
implementation, testing and characterization constitutes the
subject of this paper. We also report and comment upon
the first experimental results obtained with this new DUV
spectrograph.
CURRENT EXPERIMENTAL SETUP
We also intend to attempt the first Raman optical activity
(ROA) measurements47
within the DUV spectral region for
which the implementation of a backscattering arrangement
remains an essential requirement, especially for ROA studies
of biomolecules in dilute aqueous solution.48
We have
therefore decided to assess, at least initially, the preliminary
performance of this new spectrograph by conducting a few
selected DUV Raman studies adopting a backscattering
configuration based on the conventional ‘mirror with a
hole’ concept.49
In this section, we present a brief overall
description, focusing predominantly on the optical layout,
the charge coupled device (CCD) detection system, the
calibration of the new spectrograph and the specially
developed acquisition software.
Optical layout
As depicted schematically in Fig. 1, the beam of a quasi-
tunable continuous-wave intracavity frequency-doubled
ArC
ion laser (Coherent, Model Innova 90C FRED) pro-
pagates along the positive z-direction of a right-handed
set of space-fixed Cartesian laboratory coordinates. This
customized laser is currently capable of emitting second har-
monic wavelengths of DUV radiation at (nominally) 244, 248
and 257 nm with a beam diameter of ca 1.5 mm (appropriate
ˇ-barium borate frequency-doubling crystals for generating
laser
y
x
z
beam stop
aperture mirror
focusing
lens
sample
cell
grating
slit
edge
filter
refocusing lens
CCD
mirror
recollimating
lens
collimating lens
camera lens
Figure 1. Optical layout of the current backscattering DUV
Raman experiment at the University of Glasgow. The prefilter
double prism monochromator located between laser and
aperture has been omitted for clarity.
the other four but less intense second harmonic wavelengths
at 229, 238, 250 and 267 nm will be fitted at a later stage). The
plane of linear polarization of the DUV laser radiation is ori-
ented parallel with respect to the yz (scattering) plane, since
the frequency-doubling crystal mounted inside the laser cav-
ity causes a 90° rotation of the second harmonic plane of
linear polarization with respect to the perpendicular orien-
tation of the linear polarization plane of the fundamental
incident radiation. To help suppress residual fundamental
visible background radiation at twice the wavelength of the
incident DUV radiation, a prefilter double prism monochro-
mator, (Applied Photophysics, 8601 UV, omitted for clarity
in Fig. 1), followed by a circular stop with a diameter of ca
2 mm are mounted directly in front of the laser head. The
prefilter monochromator rotates the plane of linear polariza-
tion of the incident laser radiation by approximately 15° with
respect to the yz plane.
The beam of DUV radiation emerging from the prefilter
monochromator is directly focused into the sample by
a 25.4-mm diameter, positive best form synthetic fused-
silica lens (CVI Laser Corporation, Model BFPL-25.4–150.0-
UV-225-308) with appropriate broad band antireflection
coatings and passes through 2-mm diameter holes drilled
precisely through the centers of the two subsequent optical
elements before reaching the sample under investigation.
This focusing lens exhibits a focal length of approximately
151 mm at 257 nm and, on the basis of equations published by
Barratt and Adams,50
produces an approximately cylindrical
laser focal region of ca 13.3 mm in length and ca 33 µm in
diameter.
Laboratory air is measured directly at ambient pressure
without the use of any specially manufactured gas cells.
All solid samples on the one hand are mounted on a
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

3. 564 L. Hecht et al.
normal goniometer head (not shown in Fig. 1 for simplicity,
but a photograph of which can be found in Ref. 51 for
instance) widely used for X-ray work51
and also commonly
employed in Raman spectroscopic studies of single crystals;52
on the other hand, all liquid samples are held in specially
manufactured rectangular quartz (Spectrosil) fluorescence
cells. Depending on the DUV absorption properties of
the samples under investigation, either conventional micro
cells (6 ð 6 ð 25 mm3
, Optiglass) or macro flow cells (12.5 ð
12.5 ð 65 mm3
, Starna 46/Q) with, respectively, inner path
lengths of 5 and 10 mm and fluid compartments supporting
maximum sample volumina of 300 and 3700 µl are utilized. A
peristaltic pump (Watson-Marlow Ltd, Model 505S) is used
to rapidly circulate (120 rpm generating a flow rate of ca
4 ml s 1
inside the tubing employed) the strongly absorbing
samples under study through polypropylene based tubing
(Masterflex, Pharmed L/S 16, inner diameter D 3.1 mm)
from a minimally filled 30-ml reservoir.
The laser focus is located approximately in the core of the
sample compartment of these cells so that the DUV Raman
radiation backscattered around the negative z-direction
(180°) cannot be cutoff by the side walls of the sample
cell. In order to minimize absorption of the incident as well
as the DUV Raman scattered radiation by absorbing samples
(vide infra), the flow cells are moved slightly backwards
away from the laser, compared with the position of the
conventional cells, so that the laser focal region is positioned
as close as possible to the (entrance) exit wall of the sample
cell. Initial approximate positions of the solid samples on the
other hand, are optimized by simply searching for maximum
Raman signals.
The backscattered DUV Raman radiation emitted by the
sample is collimated by a 25.4-mm diameter fused-silica
spherical plano-convex lens (CVI, Model PLCX-25.4-12.9-
UV) with broadband antireflection coatings. Exhibiting a
focal length of 26.2 mm at 266 nm (1317 cm 1
Stokes Raman
shift with respect to 257-nm excitation), this collimating
lens has been stopped to operate at an effective ¾f/1.1
cone of collection for Stokes Raman shifts in the midwave-
number region (the central hole in this lens creates a blind
¾f/14 aperture about the backscattering direction, which
escapes collection with the current experimental setup).
The quasi-collimated backscattered DUV Raman radiation
is subsequently deflected into the 90° ( y) direction by
a plane elliptical mirror with dimensions 35.4 ð 25.0 mm2
(Optiglass), which was taken from an ROA instrument
designed for use in the visible spectral region.47
The reflecting
surface of this special elliptical mirror, an enhanced silver
coating (Balzers, Silflex), still exhibits reasonable reflectivity
in the DUV spectral region (¾29% at 258 nm) and forms an
angle of exactly 45° with respect to the xy and xz reference
planes.
Being deflected by the 45° mirror, the quasi-collimated
DUV Raman radiation penetrates a slightly tilted (ca 10°
with respect to the xz plane) 25 ð 25 mm2
square, long pass
edge filter (Barr) exhibiting relatively high absorbance values
(4.1 at 257 nm), which produce an excellent rejection of
the DUV Rayleigh scattered radiation even from slightly
opaque samples, and a very steep edge, which yields a
relatively sharp wavenumber cutoff at ca 450 cm 1
and
reasonable transmittance at longer Stokes Raman shifts (0.638
at 873 cm 1
and 0.732 at 1457 cm 1
with respect to 257-nm
excitation) for neat organic liquids (a transmission curve of
this type of edge filter for use with 244-nm excitation can be
found in Ref. 7).
Following the edge filter, the quasi-collimated DUV
Raman scattered radiation is focused by a specially designed
100-mm focal length f/2 five component calcium fluoride
camera lens (B. Halle Nachfl.) onto a 10-mm tall entrance
slit of a customized high throughput DUV version of a
single-stage spectrograph (Renishaw plc, Model System
100), originally designed for use in the visible region of
the electromagnetic spectrum. The DUV Raman radiation
entering the spectrograph through its entrance slit is
recollimated by another 100 mm f/2 calcium fluoride
camera lens (B. Halle Nachfl.) inside the spectrograph.
Two main reasons exist for using CaF2 lenses instead of
less expensive and more conventional mirror optics. The
first is that these specially designed camera lenses exhibit
far superior radiation focusing properties than appropriate
paraboloidal or ellipsoidal mirrors accounting for much less
radiation losses at the entrance slit of the spectrograph and
the focal plane of the detector (vide infra). Since we also
intend to attempt the first DUV ROA measurements, for the
success of which the use of low f/number spectrographs is
absolutely crucial,47,48
the second reason for implementing
these lenses is that, utilizing relatively short focal lengths,
such low f/numbers can be more easily realized employing
appropriate refractive rather than suitable reflective optics.
The recollimated DUV Raman radiation is subsequently
deflected by a plane 50-mm diameter circular laser line
mirror (Melles Griot, Model 02 MLQ 015/253) onto a
conventional plane, holographically recorded, 50 ð 50 mm2
square, aluminium-coated diffraction grating (Spectrogon,
Model P3600UV). The laser line mirror utilized here simply
as a spectrograph deflecting mirror consists of a synthetic
fused-silica substrate, the surface of which has been coated
with an appropriate dielectric narrow band multilayer
yielding a relatively high minimum average reflectance
(½0.97) throughout the entire DUV spectral region. The DUV
reflection grating features a symmetric sinusoidal groove
profile with a very small groove depth variation across
the entire grating surface, generating diffracted radiation
with extremely low stray light levels and without any
ghost spectral signals. The grating has 3600 grooves mm 1
producing a reciprocal linear dispersion of 1.584 nm mm 1
and operates in negative first order at an (included) angle
of D 39.5° (vide infra). The absolute efficiency of this
grating (commonly defined as the fraction of the incident flux
being diffracted into a specific diffraction order) depends on
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

4. DUV Single grating spectrograph 565
both the polarization characteristics and the wavelength of
the incident radiation. Within the relatively small spectral
range relevant to the DUV Raman work reported in this
paper, the absolute efficiency of this grating increases almost
linearly from ¾0.71 at 260.0 nm (450 cm 1
Stokes Raman
shift with respect to 257-nm excitation) to ¾0.83 at 279.7 nm
(3160 cm 1
) for incident radiation with its electric vector
oriented perpendicularly with respect to the grating grooves
(TM polarization). On the other hand, the grating efficiency
decreases from ¾0.64 at 450 cm 1
to ¾0.51 at 3160 cm 1
for radiation with its electric vector oriented parallel to the
grooves (TE polarization).
After being dispersed by the diffraction grating, the DUV
Raman radiation is, in order to maintain an f/2 acceptance
cone throughout the entire spectrometer, finally refocused by
the same 100 mm f/2 calcium fluoride camera lens (B. Halle
Nachfl.) onto the CCD sensor, which is an ideally suited
detector for a virtually shot noise limited detection of Stokes
DUV Raman scattered photons. It is placed in the focal plane
(xz here) of the spectrograph, which has a 25-mm plane
spectral field.
Detection system
We use a slow scan silicon deep depletion CCD detection
system (Renishaw plc, Model UV-RenCam) equipped with
a spectroscopic grade and advanced inverted mode CCD
sensor of rectangular physical shape (E2V, Model CCD
62-06). The exact format (8.47 ð 12.72 mm2
) of this array
comprises 578 columns by 385 rows of 221 760 individual
square pixels each measuring 22 ð 22 µm2
and each capable
of storing photo-induced electronic charge. Since the CCD
chip is oriented with its long axis parallel to the direction of
dispersion of the spectrograph, a maximum spectral coverage
of approximately 3160 cm 1
for Stokes Raman shifts can
be obtained for a fixed grating position employing 257 nm
DUV excitation resulting in an average pixel bandwidth of
ca 5.5 cm 1
.
The DUV sensitivity for this type of unthinned, front-
illuminated chip has been enhanced by employing a lumogen
DUV conversion coating. The CCD’s quantum efficiency
(QE) is nearly constant over the limited spectral range of
interest only exhibiting a slight, almost linear decrease from
ca 11.1% at 450 cm 1
(260.0 nm) to a minimum of ca 10.7% at
3160 cm 1
(279.7 nm) with the approximate numerical values
being extrapolated from a sheet of typical QE data measured
at 293 K for this type of coating (some of the existing Raman
instruments operating in the DUV spectral region8,16
offer a
superior detection with a significantly higher QE than the
relatively poor QE of the currently employed CCD detection
system in our DUV spectrograph. However, it will soon be
replaced with an appropriate backthinned DUV sensitive
array exhibiting a QE of ca 50% at 250 nm). The entire
CCD chip is cooled to ca 200 K by a four-stage Peltier effect
cooler, to produce its excellent noise characteristics with a
dark current (thermally excited signals mimicking incident
Table 1. Numerical values for black levels and the associated
RMS noise measured for the various combinations of readout
rates and amplifier gains
CCD readout parameters Black level/ADC units
Readout
rate
Amplifier
gain
Numerical
value
RMS
noise
Low High 5528 7.98
High High 4644 30.70
High Low 18 710 40.77
Low Low 21 495 12.52
radiation) of 0.00877 electron counts (e ) per pixel per second
at the operating temperature.
Basic signal processing is accomplished by a variable gain
16-bit analogue-to-digital converter (ADC), which assigns
numerical values ranging from 0 to 65 536 to each pixel.
These values are referred to as ADC units. The reciprocal
gain of the camera system, defined as the ratio of electron
counts (e ) per ADC unit, scales the full-well capacity of the
CCD (282 420 e ) to the limits of the ADC. Employing either
slow-speed or high-speed readout rates of 50 and 200 kHz,
the minimum and maximum amplifier gains of the CCD
correspond to 10.0 and 2.5 e per ADC unit respectively.
Black levels (defined as ADC values measured with zero
exposure), together with the corresponding RMS values for
the readout noise for the four different combinations of
readout rates and amplifier gains are listed in Table 1.
Spectrograph calibration
In order to facilitate the comparison of Raman spectral data,
which are obtained using a variety of monochromatic radi-
ation sources exhibiting different emission wavelengths,
Raman spectra are usually presented in standard two-
dimensional graphical form with the strength of the mea-
sured Raman signals (intensities) along the ordinate being
displayed as a linear function of the difference of absolute
wavenumbers of the laser excitation source and the individ-
ual Stokes Raman signals (relative wavenumber shifts) along
the abscissa. However, the spectrograph employed is only
capable of executing spectral scans virtually linear in wave-
lengths so that a wavelength-to-wavenumber (nm to cm 1
)
conversion is required for a convenient and comparable
presentation of all recorded Raman spectra.
Since the reflection grating in the new spectrograph is
not fixed but can be rotated for a more detailed analysis
of distinct spectral ranges, we have decided to directly
base our calculation of the Stokes Raman shift (expressed
in cm 1
) for each individual pixel of the CCD array
on a modification of the well-known grating equation.53
This equation has originally been derived for a simple
Czerny–Turner configuration and is of the following general
form:
nk D 106
[sin ˛ C sin ˇ C υ ] 1
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

5. 566 L. Hecht et al.
The quantities n and k in Eqn (1) characterize, respect-
ively, the order (dimensionless quantity) and the groove
density of the grating (quantified in grooves mm 1
), whereas
indicates the wavelength of the radiation involved
(measured in nm). The angles ˛ and ˇ are defined by
the propagation directions of the incident and diffracted
radiation with respect to the surface normal in the center of
the diffraction grating (˛ and ˇ are therefore referred to as
the incident and exit angles).53
Both these angles are related
to the included angle D ˛ ˇ; D 39.5° in our case, is the
fixed angle formed by the center lines connecting the mirror,
grating and refocusing camera lens (Fig. 1). The Greek letter υ
on the other hand, denotes the small angle at which radiation
being focused onto the CCD detector will be diffracted off
the grating, away from the central exit direction specified by
the exit angle ˇ.
The wavelength of such diffracted radiation may
be determined utilizing Eqn (1) given above, whereas its
position p, at which it is focused onto the CCD chip relative
to the center pixel of the CCD array, may be calculated using
the following relationship:54
p D f sin υ/cos υ C 2
The quantity f in Eqn (2) refers to the focal length of
our refocusing camera lens, whereas the angle indicates
the tilt of the CCD detector with respect to xz focal plane
(Fig. 1). Both these parameters have to be incorporated
into an appropriate calibration routine, since the effective
focal length of the refocusing lens ultimately depends
on the (also wavelength dependent) alignment of the
recollimating lens (Fig. 1) and even small deviations from
perfect alignment substantially alter the dispersion across
the CCD chip.
Employing a nonlinear least square fitting algorithm
according to the Levenberg and Marquardt method55
in
order to minimize the error between the known and
measured Raman band positions of a suitable calibration
sample, small variations of the two parameters f and
together with the wavelength c of the CCD center pixel
for a specific grating position finally yield an acceptable
calibration set, which is valid for a particular excitation
wavelength o. Such an optimized set of highly orthogonal
and hence rapidly converging calibration parameters (f D
98 mm, D 4.87°, c D 268.99 nm, o D 257.27 nm)
reproducibly generates Raman band positions to within
š0.60 cm 1
accuracy for cyclohexane (the spectral positions
of most cyclohexane bands are actually accurate to within
š0.40 cm 1
),56–60
which we have chosen to act as our
wavenumber calibration standard (vide infra). The reason
for this judicious choice is twofold. Firstly we intended to
avoid, at least initially, any potential complications arising
from pre-, post-, or rigorously resonant scattering regimes
demanding a completely transparent sample, which does
not show any absorption in the DUV spectral region.
From an extensive list of solvents commonly used in
spectrophotometric UV absorption studies,61
cyclohexane
appears to be a solvent that does not exhibit any significant
absorption of radiation at wavelengths longer than ½
210 nm (three distinct absorptions at 120, 143 and 159 nm
due to ! * excitations can be observed in the vacuum
UV spectral region though62,63
). Secondly, among the group
of solvents suitable for use in the DUV spectral region,
cyclohexane is one of the molecules with the most normal
modes of vibration which, despite its centrosymmetric
structure (at room temperature it adopts almost exclusively
a chair conformation with D3d point group symmetry59,64,65
)
obeying the rule of mutual exclusion, gives rise to a sufficient
number of relatively strong and well-isolated Raman-
allowed bands, which are ideally suited for wavenumber
calibration purposes. Consequently, cyclohexane has been
highly recommended for use as a Raman shift standard56
and has been used for this particular purpose in some DUV
Raman studies in the past.8,15,20
For simplicity and because here we discuss only Raman
spectra that were excited using the same laser emission
wavelength (257 nm), the spectra obtained with this new
DUV Raman spectrograph have not been corrected for
the wavelength dependence of the transmittance of the
dielectric long pass edge filter, the relative efficiency of
the diffraction grating or the QE of the CCD detector.
However, pixel-to-pixel CCD sensitivity variations, which
might cause minor intensity variations across a spectrum,
cannot be completely ruled out. It is therefore intended to
remove these sensitivity variations routinely in the future by
a method similar to that originally described by Howard
and Maynard.66
We also plan to perform a calibration
of the entire spectrograph for its absolute response in
the DUV spectral region according to standard correction
procedures published in the literature67–70
but notably those
first introduced by Graves68
and D’Orazio and Schrader.70
Acquisition software
The specially developed system software54
comprises a
native win32 application, which has been encoded employ-
ing Borland Delphi 7.0 programming language together
with some embedded assembly code altogether consisting of
approximately 56 000 lines of computer program. It is docu-
ment based, using a multiple document interface adhering
to the extensive Microsoft Windows common user interface
standard. The advantage of utilizing such a document-based
software design is that it permits the simultaneous execution
of different operations such as printing a series of recorded
spectra, which have been displayed at the same time for
comparison and have been saved within a single document
and which are to be retrieved subsequently together with all
the original format and acquisition parameters.
Internally, the software is object oriented throughout. It
uses two threads, the main thread for display and a second
thread, assigned a higher priority, for data acquisition. The
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

6. DUV Single grating spectrograph 567
hardware interface uses object drivers to encapsulate the
functionality of each device such as the CCD detector,
grating, laser or slit. The base class for each piece of hardware
defines an interface that might be used within the acquisition
thread but does not actually communicate with any hardware
device. Descendent classes comply with the interface defined
by the base class and implement the communication
with specific hardware devices such as the CCD camera.
Depending on the particular hardware configuration, the
acquisition thread assesses the functionality of a specific
hardware device through a pointer to an object that is
constructed during a particular execution cycle so that the
software may easily be expanded to incorporate different
pieces of hardware.
The software may be even further customized during
operation for different hardware configurations or may be
disconnected from the hardware altogether for separate data
analysis. It also includes a real-time display for spectrograph
alignment and sample position optimization purposes and
for defining the readout area on the CCD chip together
with a very user friendly wavelength calibration procedure
employing a cursor within a preselected calibration spectrum
in order to identify peak positions and to compare these
to appropriate numerical wavenumber values stored in a
configurable calibration file.
TYPICAL BACKSCATTERING DUV RAMAN
SPECTRA
Backscattered DUV CCD Raman spectra of liquid cyclo-
hexane, gaseous air, polycrystalline D-glucose, single crystal
L-alanine and a dilute aqueous solution of 20
-deoxyadenosine
(dA) measured at room temperature are presented in
Figs 2–6 as a brief selection of typical examples for the
excellent spectral results, which can routinely be achieved
with this new single grating spectrograph. All Raman signals
are displayed in terms of electron counts (e ) as a function
of Stokes wavenumber shifts Q with respect to the exciting
laser line (ca 38 870 cm 1
) and, apart from simple baseline
adjustments (vide infra), represent raw experimental data
directly obtained from the original Raman measurement
without the application of any cosmetic or any other spectral
manipulations.
Experimental conditions
Spectroscopic grade cyclohexane (with certified absorbances
of 0.009 at 250 nm and 0.000 at 260 nm for 10-mm pathlengths
measured against a conventional water standard) and
analytical grade D-glucose were supplied by Hopkin &
Williams and Fluka, respectively, a number of years ago.
Except for laboratory air, all other samples were purchased
from Sigma Chemical Corporation; all samples were used
directly without any further purification. Cyclohexane
was studied as a neat liquid and laboratory air was
investigated as a gas at ambient pressure, whereas L-alanine
0 500 1000 1500 2000 2500 3000
0
8
6
4
2
H
H
H
H
H
H
H
H
H
H
H
H
16 cm
-1
cyclohexane (neat)
RamanIntensity/10-3
Electron
Counts
filter cut off SNR: 200
Wavenumber / cm-1
Figure 2. Backscattered DUV Raman spectrum of neat
cyclohexane employing 257-nm excitation. The vertical
downward arrow positioned within the lower left-hand side of
the spectrum indicates the edge filter’s transmittance cutoff.
An effective resolution of ¾6 cm 1 for our DUV Raman
measurements can be estimated from the general spectral
appearance of the two partially resolved C6H12 bands
observed at ¾2925 and ¾2937 cm 1 in the C–H stretching
region. A magnified view of this doublet together with that of a
single, relatively well-isolated cyclohexane band occurring at
ca 2854 cm 1 is displayed within the inset towards the top
right-hand side of the spectrum. As indicated, a SNR of ¾200
and a nominal FWHH bandwidth of ca 16 cm 1 have been
determined for this C6H12 singlet.
1000 1500 2000 2500 3000
0
1
2
3
4 Air (ambient pressure)
6 cm
-1
6 cm
-1
SNR: 3
SNR: 6
OO
N N
RamanIntensity/10-2
Electron
Counts
Wavenumber / cm-1
Figure 3. Backscattered DUV Raman spectrum of laboratory
air at ambient pressure employing 257-nm excitation. The two
relatively sharp bands observed at ¾1555 cm 1 and
¾2330 cm 1 within the double and triple bond stretching
regions due to molecular oxygen and nitrogen species exhibit
signal-to-noise ratios (SNRs) of approximately 3 and 6,
respectively. A FWHH bandwidth of ca 6 cm 1 has been
measured for both bands.
and dried D-glucose were measured, respectively, as a
transparent single crystal (crystallized from an appropriately
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

7. 568 L. Hecht et al.
400 600 800 1000 1200 1400 1600
0
5
10
O
H
HO
H
HO
H
HO
OHH
H
OH
17 cm
-1
SNR: 50
α-D-glucose (polycrystalline)
RamanIntensity/10-3
Electron
Counts
Wavenumber / cm-1
Figure 4. Backscattered DUV Raman spectrum of pure
polycrystalline D-glucose (pressed into a pellet by the
conventional KBr disk preparation technique) utilizing 257-nm
excitation. The relatively well-isolated band observed at ca
842 cm 1, which has been assigned to a combined CH2
scissors and CO torsion mode,71 exhibits a SNR of 50 and a
FWHH bandwidth of approximately 17 cm 1.
600 800 1000 1200 1400 1600
CH3
H
CO2
NH3
12
8
4
0
B
A
L-alanine (single cry stal)
SNR: 60
SNR: 71
17 cm
-1
RamanIntensity/10-3
Electron
Counts
Wavenumber / cm-1
Figure 5. Backscattered DUV Raman spectra (A [top] and B
[bottom]) of two faces of a single crystal of L-alanine using
257-nm excitation. Spectrum B has been offset by minus 2000
electron counts in order to obtain a clearer spectral display.
The relatively well-isolated band observed at ¾852 cm 1 in
spectra A and B, which has been assigned to a highly coupled
mode consisting of C–C and C–N stretching and CO2
deformation coordinates,72 exhibits SNRs of 71 and 60,
respectively, and a FWHH bandwidth of approximately
17 cm 1 in both spectra.
concentrated aqueous solution) and as a shiny white tablet
of pure monosaccharide (prepared by the conventional KBr
disk method commonly utilized in infrared spectroscopy
employing a standard medium pressure hydraulic press and
appropriate pressing tools52,73–75
but without the use of any
alkali halogenides, which are usually added because of their
ideal cold flow properties at higher pressures). The purine
400 600 800 1000 1200 1400 1600 1800
1
2
3
N
NN
N
NH2
O
HOH
HH
HH
HO
SNR: 28
23 cm
-1
*
2′-deoxyadenosine (aqueous solution)
RamanIntensity/10-4
Electron
Counts
Wavenumber / cm-1
Figure 6. Backscattered DUV Raman spectrum of a 32.35 µM
aqueous solution of dA employing 257-nm excitation. The
dominant dA Raman band observed at ¾1336 cm 1 exhibits a
SNR of 28 and a FWHH bandwidth of ca 23 cm 1. The origin
of the relatively sharp signal observed at ca 1181 cm 1 and
denoted by an asterisk has not reliably been determined yet
but represents most likely a spurious signal owing to a laser
plasma line.
nucleoside dA was investigated as a dilute aqueous solution
at pH D 7 using doubly distilled, deionized H2O (with a
conductivity of 4 š 1 µS cm 1
measured using a standard Pt
electrode) as specified in Table 2, in which the most important
experimental conditions for the preparation of all samples
are briefly summarized.
No cells were utilized to measure laboratory air. All solid
samples were mounted on a goniometer head, whereas all
liquid samples were held in quartz fluorescence cells (vide
supra). All nonabsorbing liquid samples were studied in
a quasi-static environment. The strongly absorbing liquid
sample of dA on the other hand, in order to avoid
potential photobleaching, was investigated employing a
simple flow cell arrangement (vide supra). Water solutions
were filtered using a syringe membrane filter (Millipore,
0.4 µm pore size), to remove any dust particles before
Raman measurements were performed. Apart from the
solid D-glucose cylinder and the L-alanine single crystal,
the individually measured spectra of which showed a slight
decrease in Raman scattered intensities towards the end of
their preselected acquisition periods, we did not observe
any intensity decreases or discolorations in all the other
samples during the recording of their Raman spectra, which
might have provided evidence for sample degradation. These
observations can be rationalized by the fact that biological
molecules, which, owing to the minute concentrations and
relatively low laser powers employed, usually suffer only
mildly from slight irradiation damage in a shallow laser
focal region of partially absorbing samples, are constantly
renewed by fresh, nonirradiated molecules using a flow cell
sampling configuration. They might therefore have sufficient
time to regenerate before another exposure to laser radiation
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

8. DUV Single grating spectrograph 569
Table 2. Experimental conditions for sample preparation and the recording of the backscattered DUV Raman spectra with 257-nm
excitation presented in Figs 2–6
Figure
Sample
(origin)
Concentration/
µmol l 1
Sample
preparation
Polari-
zationa
Laser
power/
mW
Exposure
time/s
Acquisi-
tion
time/s
Selected
band
position/
cm 1
SNR
Band
width
(FWHH)/
cm 1
2 Cyclohexane
(Hopkin &
Williams)
Neat liquid None 0° 20 1 1 2854 200 16
3 Air (Laboratory) Gas (ambient
pressure)
None 90° 15 30 120 1555 3 6
2330 6 6
4 D-glucose (Fluka) Polycrystalline
tablet (1.5 mm
thick, 13 mm
diameter)
300 mg C6H12O6
dried overnight at
50 °C, pressed (13
t) into a pellet,
final pressure
held for ca 5 min
15° 17 1 10 842 50 17
5A Alanine Single crystal Crystallized from
H2O
15° 12 2 10 852 71 17
5B (Sigma) (3 ð 2 ð
1 mm3
)
60
6 20
-deoxy-
adenosine
(Sigma)
32.35 Dissolved in
water and filtered
(pore size 0.4 µm)
15° 5 120 3600 1336 28 23
a
Angular orientation of the plane of linear polarization of the incident laser radiation with respect to the yz reference plane.
in a subsequent pump cycle, whereas completely transparent
samples of pure (nonbiological) molecules, in general, do not
heat up significantly in a gently focused laser beam, even
at relatively high laser powers, because of the absence of
any physical processes that might provide access to suitable
energy transfer mechanisms.
The experimental parameters that have been adopted for
the room temperature measurement of each of the individual
DUV Stokes Raman spectra presented in Figs 2–6 are also
listed in Table 2. All spectra were excited with 257-nm DUV
radiation using laser powers of 5–20 mW, measured at the
sample using a Coherent FieldMaster laser power meter
equipped with a thermoelectric radiation probe (GS/LM-10
HTD). The width of the spectrograph entrance slit was set
to 25 µm for the recording of all spectra corresponding
to a spectral bandpass58,76
of ca 5–6 cm 1
expressed in
the conventional full-width-at-half-height (FWHH) format
(calculated as the product of the reciprocal linear dispersion
of the grating and the utilized slit width) at a wavelength
of 265 nm (1175 cm 1
Stokes Raman wavenumber shift
with respect to 257-nm excitation), which also represents
a rough estimate for the effective resolution of our Raman
measurements.
In order to increase the signal-to-noise ratio (SNR) for
the DUV Raman measurements, a serial binning mode was
employed for the CCD readout procedures using minimum
readout rates and maximum amplifier gain, which appear
to minimize black levels and also the RMS readout noise
(Table 1). Owing to the detector nonlinearities, single expo-
sure integration times were individually selected for each
sample to ensure a sufficiently large dynamic range for the
measurements yielding maximum signal heights well below
the three-quarter mark of CCD saturation (ca 45 000–50 000
ADC units) for the bands with strongest Raman intensity
in the wavenumber region of interest (8 000–30 000 electron
counts). Individual exposures employed for the recording of
the various Raman spectra are listed in Table 2 along with
the total acquisition times (calculated as the product of pre-
selected CCD exposure times and the number of spectral
accumulations involved), which ranged between 1 second
for neat cyclohexane and 1 h for the dilute aqueous solution
of dA.
Spectral results
The DUV Raman spectrum of neat cyclohexane, our
chosen wavenumber calibration standard (vide supra), in
the wavenumber region from ca 90 to ca 3050 cm 1
is
presented in Fig. 2. This spectrum was deliberately measured
without the use of the prefilter double prism monochromator
and arguably with an unfavorable choice of the state of
linear polarization of the incident laser radiation in order
to demonstrate that spectra can even be obtained under
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

9. 570 L. Hecht et al.
nonideal (nonresonant) experimental conditions. Notice the
virtually nonexistent Rayleigh signal at 0 cm 1
owing to the
excellent rejection characteristics of the edge filter employed.
However, since the transmittance cutoff of this rejection
filter, which is indicated by a vertical downward arrow
positioned on the left-hand side of the spectrum, occurs
at ¾450 cm 1
, the two lowest wavenumber bands usually
observed at ca 382 and 427 cm 1
in the Raman spectrum of a
liquid cyclohexane sample56–60
completely escape detection
with the current version of our DUV spectrograph setup.
Also note that owing to the parallel orientation of the
plane of linear polarization of the incident laser radiation
with respect to the yz (scattering) plane of the experimental
setup (Fig. 1) and, at least to a minor extent, owing to the
wavelength dependence of the transmittance of the edge
filter, the band occurring at ¾802 cm 1
and originating
in the totally symmetric and hence completely polarized
(depolarization ratio: < 0.0557
) A1g ring breathing mode77
(mainly in-phase C–C stretching coordinates78
), does not
represent the strongest Raman band in our spectrum. This is
usually the case in spectra that are excited employing visible
laser radiation with a perpendicular orientation of its plane
of linear polarization with respect to the scattering plane in
right-angle scattering (it is typically 3 times more intense
than the neighboring band measured at ca 1028 cm 1
which
has been assigned to a Eg ring stretching vibration78
).57–60
However, under rigorously resonant scattering conditions,
which usually result in significant enhancement of only
polarized Raman bands, a parallel orientation of the plane
of linear polarization of the incident radiation should be
avoided but, by implementing and appropriately adjusting
an additional half-wave plate (vide infra), a perpendicular
orientation ought to be used instead.
This chosen wavenumber calibration standard also pro-
vides an excellent opportunity to simultaneously quantify
the effective resolution achievable for our DUV Raman
measurements. A reasonable estimate for the achievable
resolution can be obtained by determining the degree of
separation of the two Raman bands observed at ca 2925
and 2937 cm 1
in the C–H stretch region of the cyclohexane
spectrum forming a nice doublet ideally suited for resolu-
tion testing purposes (the 2925 cm 1
band is associated with
a doubly degenerate Eg mode predominantly composed of
axial and equatorial C–H stretching coordinates,78
whereas
the 2937 cm 1
band originates in a totally symmetric A1g
mode mainly consisting of in-phase equatorial C–H stretch-
ing coordinates78
). From visual comparison of the general
spectral appearance of this cyclohexane doublet measured
using DUV excitation at 257 nm, as displayed in the inset of
Fig. 2 (towards the top right-hand side), with that of this dou-
blet in Raman spectra published in the literature,57–60
which
were obtained using visible excitation (435.8,59
488.0,58
514.557
and 632.860
nm) and double monochromators with relatively
high to medium resolution settings (2.0,57
4.4,58
4.660
and
6.059
cm 1
), we estimate that the effective resolution that
may routinely be achieved with our new DUV spectrograph
is approximately ¾6 cm 1
.
In addition, we have also decided to further use cyclo-
hexane for the determination of representative Raman band
SNRs, which may typically be obtained for our DUV Raman
measurements. In order to calculate reasonably quantitative
SNR estimates, we have restricted our considerations to a
sufficiently well-isolated and relatively strong Raman band
measured at ¾2854 cm 1
next to the cyclohexane doublet in
the C–H stretching region, which has been assigned to a
totally symmetric A1g normal mode mainly comprising in-
phase axial C–H stretching coordinates78
and which happens
to exhibit the highest maximum band intensity in the entire
spectrum. Following the guidelines for the determination of
more conservative SNR values of vibrational bands as sum-
marized by Schrader,79
consequently relying on maximum
baseline fluctuations in close vicinity of the selected Raman
band as a true measure of the noise for that particular band,
and employing a two-point baseline correction procedure as
suggested by Spiekermann,80
this band, as indicated in the
cyclohexane Raman spectrum depicted in Fig. 2 (towards the
lower right-hand side) and as listed in Table 2, exhibits a SNR
of approximately 200 for the experimental conditions, which
have been employed to record this spectrum. As displayed
in the inset of Fig. 2, a nominal value of 16 cm 1
has been
determined for the bandwidth (FWHH) of this ¾2854 cm 1
C–H stretching singlet.
The DUV Raman spectrum of laboratory air measured at
ambient pressure in the wavenumber region 1000–3000 cm 1
is depicted in Fig. 3. A quarter-wave plate for use at
514.5 nm functioning as a half-wave plate at 257 nm, has been
implemented between the prism prefilter monochromator
and the aperture (Fig. 1) for the measurement of this
spectrum so that the plane of linear polarization can be
rotated back to a vertical orientation (perpendicular to the
yz reference plane), which ensures slightly larger Raman
band intensities. The relatively noisy spectrum, nevertheless,
features prominently two sharp signals occurring at ca 1555
and 2330 cm 1
within the double and triple bond stretching
regions owing to molecular oxygen and nitrogen species,
respectively.81,82
As indicated in Fig. 3 and as listed in
Table 2, a FWHH bandwidth of ¾6 cm 1
has been extracted
for both Raman bands confirming the initial value for the
resolution of our DUV Raman measurements, which has
previously been deduced from the degree of separation of
the cyclohexane doublet in the C–H stretching region (Fig. 2).
However, an effective resolution of approximately 6 cm 1
is
not sufficiently high to resolve the inherent fine structure
of these bands because of the presence of isotopes and
rotational transitions, which may routinely be observed in
the Q branches of high-resolution vibration-rotation Raman
spectra of pure gases.82,83
The DUV Raman spectrum of a relatively small shiny
white tablet of pure polycrystalline D-glucose prepared by the
widely used KBr disk method (vide supra) in the wavenumber
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

10. DUV Single grating spectrograph 571
region 300–1700 cm 1
is displayed in Fig. 4 (glucose of
commercial origin largely consists of the ˛-anomer84
); it
does not absorb the incident DUV radiation. The band
positions and relative intensities in the spectral region
700–1500 cm 1
are similar to those previously published
for polycrystalline ˛-D-glucose using 647.1-nm excitation.71
The band observed at ¾542 cm 1
that has been assigned
to a ring distortion and which is the most intense band in
the Raman spectrum measured using visible excitation,71
appears to be relatively weak in the DUV Raman spectrum.
The reasons for its reduced intensity appear to be the same
as those for the reduced signal strength of the ¾802 cm 1
band of cyclohexane (vide supra).
The DUV Raman spectra from two arbitrarily chosen
faces of a single crystal of L-alanine within the wavenumber
region 500–1700 cm 1
are displayed in Fig. 5. Orthorhombic
L-alanine crystals belong to the (enantiomorphic) space
group D4
2-P212121 (No. 19), with the unit cell containing
four identical zwitterionic molecules.85,86
A few reports on
Raman scattering and infrared absorption87,88
together with
theoretical analyses72
of L-alanine exist in the spectroscopic
literature. L-alanine does not absorb the incident 257-nm
radiation used to excite the Raman spectra presented in Fig. 5.
These Raman spectra demonstrate the fine detail that may
be available from our DUV Raman measurements, especially
within the midwavenumber spectral region 1300–1500 cm 1
,
which contains a number of Raman bands of varying
intensities. Specifically, the L-alanine crystal face which
gives rise to spectrum A, displayed in Fig. 5 (top trace)
generates a Raman signal occurring at ¾1410 cm 1
with only
a tiny hint of another underlying signal, whereas a band
and a shoulder are more clearly observed at ¾1410 and
¾1422 cm 1
in spectrum B (bottom trace in Fig. 5) measured
from the other crystal face. This Davydov, or factor group
splitting, appears to be most pronounced for the Raman band
occurring at ¾1467 cm 1
in spectrum A, since two separate
bands are observed at ¾1461 and ¾1484 cm 1
in spectrum
B owing to the dominant intermolecular interactions of the
four molecules in the unit cell of the crystal.85,86
The DUV Raman spectra discussed so far (Figs 2–5)
have all been measured using samples that do not absorb
the incident laser radiation at 257 nm, so that their spectra
have been measured under nonresonant Raman scattering
conditions. Consequently, we also wanted to investigate
whether or not our current backscattering geometry is also
suitable for obtaining Raman spectra of strongly absorbing
samples within the realm of pre-, post- or rigorously resonant
Raman scattering regimes. As our test sample for evaluating
a resonant scattering scenario, we have therefore chosen
the purine nucleoside dA, which has been shown by NMR
studies to favor the S conformation (71% at 25 °C) in aqueous
solution.89
At pH D 7, it exhibits a relatively strong electronic
absorption (ε260 D 15 200 l mol 1
cm 1
)90
at 260 nm (450 cm 1
Stokes wavenumber shift with respect to 257-nm excitation),
being sufficiently close to the selected Raman excitation
wavelength.
The DUV Raman spectrum of an aqueous solution of dA
in the wavenumber region 400–1800 cm 1
is shown in Fig. 6.
Initial efforts to obtain Raman spectra from an aqueous
530 µM dA solution, as published by Wen and Thomas,91
proved unsuccessful because of the strong self-absorption of
both the incident laser and the Raman scattered radiation.
Subsequent dilution to ca 32 µM allowed a Raman spectrum
of dA to be measured successfully with the dominant band
observed at ¾1336 cm 1
, which has been assigned to a
C5N7 and N7C8 stretching mode of the purine ring,91
being
positioned between the two relatively broad water signals
occurring at ¾740 and ¾1620 cm 1
at the left- and right-hand
side of the spectrum (the lower wavenumber signal may
be interpreted as arising from symmetric and antisymmetric
stretching coordinates of the water hydrogen bonds92
). The
origin of the relatively sharp signal observed at ¾1181 cm 1
and indicated by an asterisk remains unclear at present
but, on account of its shape, arises most likely from a laser
plasma line (occurring at 530.58 nm in air), which has not
been fully suppressed so that it still features prominently in
this relatively weak dA Raman spectrum.
Although the dA Raman spectrum obtained by Wen and
Thomas,91
also utilizing 257-nm excitation evidently exhibits
a better SNR than our dA spectrum displayed in Fig. 6,
it is difficult to compare these two dA DUV Raman spectra
semiquantitatively, since the acquisition time of the literature
spectrum, which has also been background subtracted,
has unfortunately not been disclosed. The relatively long
acquisition time of 1 hour for the measurement of our
dA Raman spectrum may therefore be rationalized by the
relatively low dA concentration utilized, as compared with
the approximately 17 times more concentrated solution
used to obtain the literature dA reference spectrum,91
the implementation of an optical system for focusing the
incident laser radiation and the collection of backscattered
Raman radiation, which appears to be nonideal for strongly
absorbing samples within the resonant scattering regime.
Radiation in the approximately cylindrical laser focal region
with a length of ca 13.3 mm (vide infra) is strongly absorbed by
the dA sample. Only ca 1 mW of the incident 5 mW of DUV
laser radiation emerges from this focal region in accordance
with the rapid exponential decrease in laser power with
increasing distance as stated in the Bouguer-Lambert-Beer
law.93
Similarly, the intensity of the backscattered Raman
radiation is also expected to drop exponentially with
increasing penetration depth through the aqueous solution of
dA in accordance with its relatively large molar absorptivity
at the Raman shifted wavenumbers.90,93
Future resonant
Raman scattering experiments will consequently use a laser
focusing lens (Fig. 1) of much shorter focal length in order to
significantly reduce the dimensions of the laser focal region
and to minimize absorption of the incident laser and Raman
scattered radiation, thereby permitting further optimization
Copyright  2005 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2006; 37: 562–573

11. 572 L. Hecht et al.
of experimental conditions and consequently enabling the
recording of spectra from strongly absorbing samples with
much greater ease.
CONCLUSIONS
Using relatively expensive, but state-of-the-art commercially
available components, we have succeeded in developing a
new single grating spectrograph for Raman studies within
the DUV spectral region. Owing to the implementation of
superior grating and filter technology and specially designed
five component calcium fluoride lenses, its large angle
of collection (f/2) and its narrow spectral bandpath (ca
6 cm 1
), this new DUV CCD Raman spectrometer at Glasgow
University is currently one of the best in terms of throughput
and characteristics related to overall performance. It is
capable of measuring sufficiently large SNRs in much faster
acquisition times and with much higher resolution than any
other DUV Raman instrument described in the literature to
date. Its excellent speed of detection will even be further
increased once the currently employed front-illuminated
CCD chip exhibiting relatively small QE values will be
replaced by an appropriate back-illuminated sensor with
significantly larger QEs.
Acknowledgements
We thank the Scottish Higher Education Funding Council (SHEFC)
for a research development grant (RDG 115) to Lutz Hecht as
one of the coapplicants and Johnson Matthey for funding John
Clarkson. We acknowledge Prof. P. C. Stair’s suggestion to measure
the spectrum of air with our new DUV Raman spectrograph. We are
grateful to Dr J. Smith for reading and commenting on the typescript.
We would also like to express our sincere gratitude to Dr D. Lennon
for his initial suggestion to launch a Glasgow DUV Raman project,
his unshattered persistence in directing sufficient funds towards
this new project and for his continuous encouragement throughout
the entire design and construction period of the DUV spectrograph.
Many thanks David!
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