Laser Laboratory

We have demonstrated that laser beam can be focused through diffusive media such as a ground glass or biological tissue onto a light absorber by shaping the wavefront.

Fanting Kong, Ronald Silverman, Liping Liu, P. V. Chitnis, Kotik K. Lee, and Y.C. Chen, "Photoacoustic-guided convergence of light through optically diffusive media", Opt. Lett. 36, 203 (2011).  PDF

Multimode fibers are a closed system of diffuse reflectors. The interference among the fiber modes creates a random granular pattern, known as speckle, at the output and causes a total loss of spatial coherence. We have demonstrated that the coherence of the beam transmitted through multimode fibers can be restored by wavefront shaping. This can be done at the input or output ends. Potential applications include delivery of a focused laser beam through an endoscope for laser surgery.

Using focused laser beam to generate ultrasound with pinpoint precision, we have achieved 20-fold improvement in the resolution of photoacoustic images compared to conventional ultrasound images.

Potential applications of this technique include clinical examination of superficial and thin tissues containing optically absorbing pigments such as melanin or hemoglobin, including skin, mucosa, and ocular tissues (iris, retina and choroid).

Reference:
Fanting Kong, Y.C. Chen, Harriet O. Lloyd, Ronald H. Silverman, Hyung Kim, Jonathan M. Cannata , and K. Kirk Shung, “High-resolution photoacoustic imaging with focused laser and ultrasonic beams”. Applied Physics Letters, 94 , 033902 (2009).

By using a spatial filtering technique we have recently achieved simultaneous and phase-locked generation of short pulses in a two-element fiber laser system. The nanosecond Brillouin-scattering pulses are intense enough to self-destruct the fiber core. We are currently working to apply this technique to phase locking in two-dimensional fiber laser arrays containing many more elements.

Reference:
Fanting Kong, Liping Liu, Charlotte Sanders, and Y. C. Chen, and Kotik K. Lee, “Phase locking of nanosecond pulses in a passively Q-switched two-element fiber laser array”, Applied Physics Letters, 90, 151110 (2007).

• Frequency-tripled and -doubled Nd:YAG laser pumped dye laser (Lambda Physik) operating in the wavelength range from 400 nm to 1000 nm.
• Frequency-doubled Nd:YAG laser pumped optical parametric oscillator (OPPO) tunable in the wavelength range from 600 nm to 2000 nm.
• CW Q-switched mode-locked Nd:YAG laser (fiber-compressed to 1 ps) with electro-optic single pulse selector, and auto-correlator.
• 100-Watt Carbon dioxide laser for material processing.
• CW-pumped 1-kHz-repetition-rate Nd:YAG regenerative amplifier.
• Diode-pumped solid-state lasers, including 808-nm-pumped Nd:YAG lasers, Nd:glass lasers, self-Q-switched Nd:YAG lasers, and 670-nm-pumped Cr:LiSrAlF6 lasers, and regenerative amplifier pumped by 30 W diode lasers.
• Pockels cells, acouto-optic modulators and shutters.
• High-power diode lasers covering 630-670 nm, 750-1200nm.
• Mode-locked semiconductor lasers with 5-ps pulse duration, high-power semiconductor lasers, frequency stabilized semiconductor lasers.

• Tektronix SCD 5000 transient digitizer with 5GHz bandwidth.
• Tektronix TDS684 and TDS784 digital oscilloscopes with 1 GHZ bandwidth, Tektronix 11801 sampling oscilloscope with 20 GHZ bandwidth.
• Tektronix 7104 oscilloscope with 7A29 and 7B10 plug-ins (1GHz bandwidth), 7T11 and 7S11 plug-ins (25 GHz sampling), DCS-01 trace digitizing camera system, Tektronix 7603 oscilloscope with 7A26, 7B85 and 7A19 plug-ins.
• Lock-in amplifiers, box car integrators.
• Thermoelectric temperature controllers for diode lasers.
• Hewlett Packard 8554B/8552B/8555A spectrum analyzer, Tektronix 7L13 spectrum analyzer.

• Fourier-transform IR spectrometer (Nicolet 760) for wavelength ranging from 0.4 microns to 16 microns.
• Fourier-transform Raman spectrometer.
• Optical Multichannel Analyzer (OMA) spectrograph.
• Spex 1702 3/4-meter spectrometer, two Jarral Ash 1/2-meter spectrometers.
• Burleigh confocal scanning Fabry-Perot interferometer, Tec Optics scanning Fabry-Perot interferometer.

• Evaporator.
• Cutting, polishing and lapping machines for optical materials.

• Cooled InGaAs detector array.
• High speed InGaAs and Si detectors with 40 GHz bandwidth.
• CCD Detector arrays, pyroelectric detector arrays, infrared TV cameras with PbO2 and Si tubes, North Coast liquid-nitrogen-cooled Ge p-i-n detector with preamplifier and muon filter, high-speed Si, Ge, InGaAs and GaAs p-i-n and avalanche photo-diodes.
• Photon-counting system.