Overview
Overview
Current laser development projects include new UV, Visible and IR sources for life sciences, frequency-agile deep-UV (UV-C) Resonance Raman sources for stand-off detection and remote sensing, novel coherent LIDAR systems, and compact, tunable single-mode DPSS sources for gas-phase oxygen and CO2 sensing.
Custom flash-lamp pumped medical lasers
Custom flash-lamp pumped medical lasers
John is a dinosaur an expert in the design and development of high-repetition-rate, high-peak-power, flashlamp-pumped, solid-state 1, 2 and 3 micron (µm) lasers used in medical therapeutics and some materials processing applications. Past projects include new high-power low-M2 CTH:YAG (chromium-thulium-holmium yttrium-aluminum-garnet) 2-µm lasers for novel lithotripsy procedures, HoLEP/ HoLAP (Holmium Laser Enucleation of the Prostate, Holmium Laser Ablation of the Prostate), and low M2 2.94 micron Er:YAG lasers for incisional surgery with low HAZ (thermally-coagulated, non-viable Heat-Affected Zone).
A particularly interesting application is the development of a long-pulse, near-degenerate OPO pumped at 1 micron and emitting at 1.9 – 2.1 microns for investigations in laser lithotripsy optimizing the wavelength and pulsewidth to create the optimum shock wave conditions. The OPO also creates a very high beam-quality pulse, suitable for injection into small-core, multi-mode fibers which can get to the lower pole of the kidney without suffering catastrophic optical failure under high laser powers when the bend radius of the fiber is small, thus preventing catastrophic damage to the ureteroscope.
John has worked on pulsed Q-switched alexandrite lasers for deep UV generation (Bibliography – John F Black et al) and a new generation of Q-switched Nd:YAG lasers at 1064 and 532 nm for both tattoo removal and, more recently, a new process for continuous in-line generation of metal nanoparticles at very high concentrations and with tight monochromatic size distributions. The latter development resulted in a single-rod oscillator capable of tunable repetition rates between 5 – 30 Hz with only moderate changes in beam quality, and over 800 mJ per pulse in sub-5-ns pulses continuously variable between 5 and 25 Hz. An additional amplifier stage could produce over 2 Joules per pulse at 1064 nm with an expectation for around 1 Joule at 532 nm with KTP second-harmonic generation. John has also built lamp-pumped, injection-seeded SLM pulsed lasers for OPO pumping for both tunable visible and IR generation, and is well-versed in non-linear optics for both lamp-pumped and DPSS / fiber laser applications.
DPSS Lasers
DPSS Lasers
John is also skilled with diode-pumped solid-state (DPSS) lasers, having worked on DPSS green, yellow and red lasers for ophthalmic photocoagulators, novel green and blue fiber lasers for RGB projectors (Bibliography – Kane et al., 2004) (http://sonypremiumhome.com/pdfs/VPL-VW5000ES-whitepaper-VG.pdf).
He was the lead optical engineer on the ground-breaking Xcyte™ compact mode-locked, frequency-tripled diode pumped Nd:YAG laser.(Myers et al., 2005) (https://www.lumentum.com/en/products/laser-solid-state-quasi-cw-355-xcyte), a mode-locked quasi-CW (QCW) laser producing 355 nm pulses at 100 MHz for flow-cytometry applications in a remarkably compact chassis with the beam pointing stability traditionally associated with much larger platform mode-locked lasers.
VROC / GRM Lasers
VROC / GRM Lasers
John is an even bigger dinosaur an expert in the design and development of electro-optically and passively Q-switched Variable Reflectivity Output Coupling (VROC) positive-branch unstable resonators (often called Gaussian Reflectivity Mirror (GRM) or super-Gaussian lasers).
The heart of a VROC cavity is the so-called Gaussian mirror, pictured below, where a dot of reflective material, most often a refractory transition metal oxide layer, of variable thickness over the dot radius is deposited on an AR-coated lens substrate.
The varying thickness of the dot over the radius causes the reflectivity of the dot to vary, from essentially 0% at the edges to some value Rmax in the center of the dot. The FWHM of the dot, the peak reflectivity and the shape of the dot (Gaussian, super-Gaussian, other more complex waveforms) is selected to balance the needs of the end user. It is possible to tailor the properties for energy extraction vs. mode quality, with (generally) less energy coming from a resonator whose beam quality (M2) approaches the physical limit (~1.X).
For a mid- or meso-field application such as tattoo removal or ablative nanoparticle creation where the beam is used at a range of a few meters, a super-Gaussian mirror extracts a large amount of energy in an approximately flat-topped beam with higher-frequency diffraction rings subsumed into the overall envelope. This ensures approximately constant fluence over the target for reproducibility and consistency.
For a far-field application, such as LIDAR, a true Gaussian reflectivity profile produces the smoothest, lowest mode order beam that will propagate “as-is” without the emergence of diffraction rings.
John recently designed and tested a novel single-rod super-Gaussian cavity that produces ~4 nanosecond (ns) FWHM pulses at a variable repetition rate of 5 – 25 Hz with minimal changes in beam shape and maintaining > 800 mJ per pulse over the full range of repetition rates. He also designed a novel functional form for the shape of the reflectivity profile on the mirror that optimizes energy extraction in the case that the end user requires a more-true-Gaussian, low-mode-order beam, but with more energy than can be typically extracted from a traditional GRM. The shape is a bridge between a true GRM and a super-Gaussian design.