Laser Broadening

1. L SER
Submitted to : Dr. Umesh Kumar dwivedi
Prepare By : Surendra singh
Course : M.sc (AP)
Semester : 3rd
Amity university Jaipur

2.  LINE SPECTRA
In an atom electrons are revolving around the nucleus in different
discrete energy levels when energy is provided, electron jumps from
lower energy level E1 to higher energy level E2 and atom is excited but
shortly atom de excites and emit photon of energy E=hʋ this process is
spontaneous emission and spectrum thus produced by an atom is in
the from of line called line spectra having fixed frequency and fixed
energy.

3.  BROADENING
It was always thought that laser is monochromatic or it is a single
frequency beam of light. The idea of a monochromatic laser is not
quite true. The fact is that the laser beam spectrum has a defined line
shape and not just a single point on the spectrum.
This phenomenon is called laser broadening and the measure of it is
called line width.
we ideally expect a single line showing single frequency or emitted
spectra. But in reality the difference between the two energy level is
not fixed energy because of splitting of energy levels into further sub
levels and difference photons of different energy are emitted due to
de excitation, so frequency range spread.

5.  Lineshape Function :
Define lineshape function g(ʋ) such
that g(ʋ)dʋ gives the probability that
a transition between two levels is an
emission (or absorption) of photon
whose frequency lies in the range ʋ
and ʋ+dʋ . Normalization demands
For N number of electron

6. BROADENING
HOMOGENEOUS INHOMOGENEOUS
NATURAL OR
INTRINSIC
COLLISION DOPPLER LOCAL FIELD

7. If the fluctuation in the frequency/wavelength is due to a phenomenon
that is the same for each quantum emitter, there is homogeneous
broadening. In other word, By homogeneous broadening we mean that
the line of each atom broaden in the same way. In this case the line shape
of the single atom cross section and that of the single overall absorption
cross section are identical.
 HOMOGENEOUS BROADENING

9.  NATURAL OR INTRINSIC BROADENING
It originates from spontaneous emission since this emission is a feature of
any transition the corresponding broadening is called natural or intrinsic.
The quantum electrodynamics theory of spontaneous emission shows that
the spectrum is again described by a lorentzian line.

10. CONT…
Natural linewidth is an inherent width associated with any energy level due
to quantum mechanical uncertainty principle. According to this principle,
Δt if is the minimum uncertainty in the lifetime of an atom in an energy
level, the uncertainty in determining the energy level itself is given by
ΔE Δt ~ h/2Л
Using E = hʋ , the relation may be written as
Δʋ Δt ̴ 1/2Л

11.  COLLISION BROADENING
In a gas or a liquid it is due to the collision of an atom with other atoms,
ions, free electrons etc. or with the wall of the container.
In a solid it is due to the interaction of the atom with the lattice phonons.

12. source
System
I
ʋ

13.  INHOMOGENEOUS BROADENING
Inhomogeneous broadening is an increase in the linewidth of an atomic
transition caused by effects which cause different radiating or absorbing
atoms (or ions) to interact with different wavelength components.This
means that the absorption and emission cross sections have different
spectral shapes for different atoms.

14.  DOPPLER BROADENING
Doppler broadening is also inhomogeneous broadening which is produced
due to motion of atom.
Different frequency of spectrum are observed due to relative motion of
atoms.
This equation shows relative Doppler frequency
f = f0 (1+v/c) and f = f0 (1-v/c)
Where v is speed of atom, f is apparent frequency of spectra, f0 actual or
proper frequency.

15. Detector
Container
In the case of the thermal Doppler broadening, the velocity distribution is
given by the Maxwell distribution :
Where is m the mass of the emitting particle, T is the temperature, and k is
the Boltsmann constant

16. CONT…
Gaussian profile with the standard deviation
and full width at half maximum (FWHM)

17.  Population Inversion :
For light amplification by stimulated emission of radiation the population
of excited state must be greater than the population of lower energy state
this condition is called population inversion.

19.  GAIN MEDIUM
The active laser medium (also called gain medium or lasing medium)
is the source of optical gain within a laser. The gain results from
the stimulated emission of electronic or molecular transitions to a lower
energy state from a higher energy state previously populated by a pump
source.
Examples of active laser media include:
1.In solid laser, typically doped with rare-earth
ions (e.g. neodymium, ytterbium, or erbium) or transition metal ions (titanium
or chromium); most often yttrium aluminium garnet (Y3Al5O12), yttrium
orthovanadate (YVO4), or sapphire (Al2O3); and not often Caesium cadmium
bromide (CsCdBr3)

20. 2. Glasses, e.g. silicate or phosphate glasses, doped with laser-active ions.
3.Gases, e.g. mixtures of helium and neon (HeNe), nitrogen, argon, carbon
monoxide, carbon dioxide, or metal vapors.
4.Semiconductors, e.g. gallium arsenide (GaAs), indium gallium
arsenide (InGaAs), or gallium nitride (GaN)
5.Liquids, in the form of dye solutions as used in dye lasers.
CONT…

21. Thank You