Tunable Cr:F Femtosecond Lasers
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Tunable Cr:F Femtosecond Lasers

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  • Use a ytterbium doped fiber laser instead of the typical neodynium:YAG diode pumped laser Extremely compact size. About the size of a shoe box. Intrinsically no mode-beating with a noise level of < 0.1% The Yb:fiber diodes have a much longer lifetime than the Nd:YAG diodes.
  • 1) Allow the detection and study of short-lived transient chemical reaction. 2) The generation of tunable ultrashort laser pulses has particular significance for the study of the rapid events that arise in photochemistry and photobiology.
  • Center at 1250nm extends from 1100 to 1400nm Compliments Cr 4+ :YAG and Ti:Sapphire Semiconductors transparent to longer wavelengths Broad absorption spectrum Low scattering from biological samples when compared to Ti:Sapphire Absorption lower than for 1500nm Cr 4+ :YAG
  • Low scattering from biological samples when compared to Ti:Sapphire Absorption lower than for 1500nm Cr 4+ :YAG
  • Close to zero dispersion wavelength of optical fiber
  • Non-linear optical methods, such as second- and third-harmonic generation, are well-known spectroscopic techniques for providing structural information about the Surface of materials methods are non-linear optical methods, they rely on the use of a high-intensity laser source. Typically, the Ti:sapphire laser is considered as the major source of femtosecond pulses for non-linear optical microscopy studies. We have shown an advantage of our laser by demonstrating microscopic imaging using the Cr4+:forsterite oscillator. We noted that the radiation of the second harmonic ( λ = 625 nm) and third harmonic ( λ = 417 nm) of the Cr4+: forsterite laser is in the transparent region for conventional microscope objectives, while the detection efficiency is still high compared to the third harmonic of the Ti:sapphire laser ( λ = 266 nm). Moreover, most photo detectors for visible radiation are completely blind to 1250-nm radiation, making weak signal discrimination easier and less expensive (since off-the-shelf components can be used). Nonlinear optical effects Two-photon and Three-photon Fluorescence Third Harmonic Generation (THG) Significantly improve the depth resolution Reduced background noise
  • In THG, one must use a longer wavelength laser (>1.0 µm) in order to avoid direct absorption of the third harmonic by the specimen. Second and third harmonic of Cr:Forsterite in or close to the visible. Easily detected by standard components.
  • Third harmonic light is produced on both sides of the focus THL destructively interferes If a index interface is within the focal plain. THG symmetry is broken Totally destructive interference does not occur Some of the THL light is emitted
  • Detecting THG emission localized to interfaces Interface detected with high contrast even with modest NA optics. In this 0.6 NA was used. Note the increase in signal at the interfaces. So THG imaging yields an image of the interfaces of the specimen.
  • THG images of neurons in a cell culture. The size of the cell’s soma is about 15 mm. 100 fs pulses at 1.2 µm, 1 kHz repetition rate
  • Cross-sectional micron-scale imaging In situ and in real time, without the need for tissue excision and processing Catheter / endoscope imaging of internal organs Consistent with Minimally Invasive Surgery Electronic information enables processing, storage, transmission Commercial device available for ophthalmologists
  • OCT measurement as defined by the signal detected at the output of the interferometer is the electric-field autocorrelation of the source. The coherence length of the light is the spatial width of the field autocorrelation, and the envelope of the field autocorrelation is equivalent to the Fourier transform of its power spectrum. Thus, the width of the autocorrelation function, or the axial resolution, is inversely proportional to the width of the power spectrum. That high-axial resolution requires broad bandwidth optical sources. Low coherence light source Ref arm and sample arm must match within the coherence length of the optical source Axial resolution is determined by the coherence length of the light source Uses Michelson interferometer to look at the coherence of back scattered light Need large bandwidth Down to 2 micron res The broadband nature 200 nm of bandwidth of cr:f gives a very high resolution
  • Most chemical reactions occur on a femtosecond(10-15)s time scale. Femtosecond laser spectroscopy concerns itself with monitoring chemical reactions in real time. One way to do this is to use a pulsed laser system to initiate and then probe the reaction. The probe pulse is delayed with respect to the initiation (pump) pulse by splitting the original femtosecond pulsed beam and allowing one portion to travel further along the optical bench than the other. In the femtosecond time regime this is achievable with a distance scale of microns The short pulse duration allows the detection and study of short-lived transient chemical reaction at very high resolutions
  • Laser drilling Laser Welding The femtosecond pulse duration is very short making even low energy pulses produce extremely high peak power. This limits low energy threshold thermal and mechanical side effects. The high peak power of the femtosecond pulse allows multiple photons to be absorbed, creating an electron plasma in the material. As the plasma expands material is ejected from the target area. 10 Because this material ablation is not a thermal effect, cavitations and laser induced pressure transients are reduced. Femtosecond lasers are used to produce micro-gratings and multi-dimension periodic nano structures in a variety of materials including dielectrics, semiconductors, metals, plastics and resins [a1] . 11 Multiphoton absorption allows for processing of materials that are not very photosensitive. Below the ablation threshold the high pulse energies can introduce structural changes resulting in a change in the index of refraction of the material. All optical wave guides and photonic devices are manufactured using these techniques. 12   [a1] Old papers #4
  • The same properties that make femtosecond lasers useful for material processing can also be used for a variety of surgical applications.
  • One of the first commercially successful applications of femtosecond lasers is their use in the LASIK (Laser in situ keratomileusis) eye surgery procedure. Cr4+ lasers in 1110-1500 nm range offer safer wavelengths than Ti:sapphire femtosecond lasers at 800 nm to reduce potential retinal damage. The Ultrafast laser replaces the microkeratome mechanical knife that makes the initial cut in the cornea. This offers a highly controlled cut of uniform thickness that is not possible with a mechanical knife
  • The extremely clean material processing abilities of femtosecond lasers offer an alternative to mechanical drills or CW lasers that leave micro cracks and cause thermal stress in tooth enamel
  • X-ray diffraction temporally resolved on the femtosecond time scale is a strong instrument for studying ultrafast processes in all the fields of scientific interest, from biology to physics and chemistry. The development of the laser-plasma source for producing femtosecond X-ray flash has given rise to the first applications of this technique to follow dynamical processes [1]. Such Compton sources, often called as glaser synchrotronh, can provide some of the important benefits like good beam collimation, monochromatic, short pulse width in ps-fs region, and a compact system

Tunable Cr:F Femtosecond Lasers Tunable Cr:F Femtosecond Lasers Presentation Transcript

  • Tunable Cr:F Femtosecond Lasers Charlie Barnes & Andy Carson Del Mar Ventures Research and Industrial Applications
  • Femtosecond Products Offered By Del Mar Ventures
    • Pulse Pickers
    • Femtosecond Autocorrelators
    • Femtosecond Fluorescence Systems
    • Wavelength Converters
    • Ti:Sapphire Lasers
    • Ti:Sapphire Multipass Amplification Systems
    • Cr:Forsterite Lasers and TW Systems
  • Introduction to Cr:F Lasers
    • Center wavelength of 1250 nm
    • Tunable from 1100—1400nm
    • Broadband absorption
    • Directly pumped by Ytterbium Fiber Laser
    • Sensitive to thermal effects
  • Continuous Beam vs. Ultrashort Pulses Continuous Beam (Ideal Case) Ultrashort Pulses (Ideal Case)  
  • Short Pulses vs. Long Pulses  
  • Mode-locking Multimode Lasers Time RANDOM phase for all the laser modes Irradiance vs. Time Out of phase Time
  • Out of phase Time Out of phase In phase Irradiance vs. Time Time LOCKED phases for all the laser modes Mode-locking Multimode Lasers
  • Mode-locked pulses Ultrafast lasers have thousands of modes!
  • How do we mode-lock the laser? Kerr-Lensing Low-intensity beam Kerr medium (n = n 0 + n 2 I) High-intensity ultrashort pulse Focused pulse
  • Making a mode-locked laser CW Pulsed Power Time Power Time c/2l Barrier High loss Low loss
  • Elements of Cr:F ultrafast laser Output Coupler Dispersion Compensating Prisms Yb:fiber Pump Laser Lens Curved Mirrors Cr:F Laser Crystal High Reflector High Reflector
  • Pump Laser
    • Yb:fiber pump laser
    • Extremely compact size
    • No mode-beating
    • Noise level < 0.1%
    • Longer lifetime
    • Costs 50% less than comparable Nd:YAG
  • Chirped Pulse Amplification Oscillator Stretcher Amplifier Compressor
  • TerraWatt System Pump Laser: PYL-10 1060 nm, 10 W Pump Laser: 1060 nm 30 ns, 30 mJ, 10 Hz Oscillator Regenerative Amplifier Stretcher 1250 nm 40- 80 fs 100 МHz 2 nJ 1250 nm 200 ps 10 Hz 0.5 mJ 1250 nm 200 ps, 10 Hz, 200 mJ 1250 nm 60 – 80 fs, 10 Hz, 120 mJ 1 – 2 TW Pump Laser: 1060 nm 30 ns, 0.7 J, 10 Hz Compressor Pump Laser: 1060 nm 30 ns, 1 J, 10 Hz 1250 nm 200 ps 10 Hz 50 mJ Multipass Amplifiers
  • Research and Industrial Applications
    • High Resolution Imaging
    • Photochemistry And Photobiology
    • Material Processing
    • Medical Applications
    • High Energy Physics
  • Advantages Femtosecond Lasers
    • Short pulse duration
    • Broadband
    • Very high resolutions
    • Less dispersion
  • Emission Spectra Cr:Forsterite Ti:Sapphire Cr:Forsterite Cr:YAG 1500 nm 1250 nm 800 nm
  • Advantages Cr 4+ :Fosterite Ti:Sapphire Cr:Forsterite Cr:YAG
  • Cr 4+ :Fosterite High speed communications Dispersion Attenuation
  • Imaging with Ultrashort Laser Pulses
    • Non Linear Effects
    • in vivo
    • Significantly improve the depth resolution
  • Third harmonic generation Multi-Photon Microscopy Three photon fluorescence Two photon fluorescence  t  t
  • Third Harmonic Imaging Index change breaks symmetry High intensities create non-linear optical effects THL destructively interferes THL both sides of focus
  • Third Harmonic Imaging Interfaces
  • THG Neurons 15 µm Optical fiber in index-matching fluid D. Yelin and Y. Silberberg 125 µm
  • Optical Coherence Tomography
    • Micron-scale cross-sectional
    • in vivo imaging
    • Real time
  • Low Coherence Interferometry Low-Coherence Source Coherence Length Mirror Displacement Detector Reference Detector Mirror Displacement High-coherence Source Detector Michelson Interferometer Sample Source  / 2
  • OCT Images Live Tadpole Blood Vessel
  • Femtosecond Spectroscopy
    • Most chemical reactions occur in 10 -15 sec
    • Femtosecond spectroscopy monitoring reactions in real time
    • Short pulse duration allows the detection short-lived transient chemical reactions
  • Pump and Probe
    • Medium is excited with femtosecond pulse
    • Delayed probe pulse by increasing path length (microns)
    • Short pulse duration allows short-lived reactions to be studied
    • Very high resolutions
  • Material Processing
    • High peak power, TW with amplified systems
    • Mulitphoton absorption
    • Low thermal and mechanical side effects
    • Ablation
    • Induced structural changes
  • Material Ablation
    • Photons generate electrons
    2) Electron avalanche 3) Plasma expansion 4) Electron-phonon coupling 5) Material is ejected e -
    • Variety of materials including dielectrics, semiconductors, metals, plastics
    • Multiphoton absorption allows for processing of materials that are not very photosensitive.
    (Herbert Welling, Laser Zentrum Hannover) Material Processing 200 fs pulse 2.3 ps pulse
  • What can we make?
    • Micro gratings and periodic nanostructures
    • Machined parts for industrial and medical applications
    • Subsurface wave guides and all optical components
  • Medical
    • Laser Surgery
    • Medical biopsy
    • Hard tissue processing
  • Corneal flap removal in LASIK (Gerard Morou, University of Michigan)
  • Applications in dentistry
    • Alternative to mechanical drills and CW lasers
    • Reduced thermal stress
    • And micro cracks in enamel
  • Femtosecond X-Ray Pulses
    • Femtosecond X-ray pulses probe core electronic levels
    • Indication of the structural changes
    • Femtosecond X-rays can be generated through scattering visible laser beams by high energy electrons .
  • Conclusion
    • Many industrial and research applications
      • High Resolution Imaging
      • Photochemistry And Photobiology
      • Material Processing
      • Medical Applications
      • High Energy Physics
    • Del Mar Ventures offers a wide variety of femtosecond products
  • Thank you for coming Charlie Barnes and Andy Carson Del Mar Ventures