Showing papers by "Lawrence Shah published in 2016"
TL;DR: In this paper, a self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength λ 1/2μm was used to selectively modify the front and back surfaces of various uncoated and metal-coated silicon and gallium arsenide wafers utilizing transparency of semiconductors at this wavelength.
Abstract: A self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength λ = 2 μm was used to selectively modify the front and the back surfaces of various uncoated and metal-coated silicon and gallium arsenide wafers utilizing transparency of semiconductors at this wavelength. This novel processing regime was studied in terms of the process parameter variations, i.e., pulse energy and pulse duration, and the corresponding modification fluence thresholds were determined. The results revealed nearly debris-free back surface processing of wafers, in which modifications could be induced without affecting the front surfaces. The back surface modification threshold of Si was significantly higher than at the front surface due to non-linear absorption and aberration effects observed in experiments. A qualitative study of the underlying physical mechanisms responsible for material modification was performed, including basic analytical modeling and z-scan measurements. Multi-photon absorption, surface-enhanced absorption at nano- and microscopic defect sites, and damage accumulation effects are considered the main physical mechanisms accountable for consistent surface modifications. Applications of trans-wafer processing in removal of thin single- and multi-material layers from the back surface of Si wafers, both in single tracks and large areas, are presented.
22 citations
TL;DR: In this article, the authors demonstrate selective spatial mode amplification in a few mode, double-clad Yb-doped large mode area (LMA) fiber, utilizing an all-fiber photonic lantern.
Abstract: We demonstrate selective spatial mode amplification in a few mode, double-clad Yb-doped large mode area (LMA) fiber, utilizing an all-fiber photonic lantern. Amplification to multi-watt output power is achieved while preserving high spatial mode selectivity. We observe gain values of over 12 dB for all modes: LP01, LP11a, and LP11b, when amplified individually. Additionally, we investigate the simultaneous amplification of LP01+LP11a and LP11a+LP11b, and the resultant mode competition. The proposed architecture allows for the reconfigurable excitation of spatial modes in the LMA fiber amplifiers, and represents a promising method that could enable dynamic spatial mode control in high power fiber lasers.
18 citations
TL;DR: This Letter demonstrates DPA of picosecond pulses in a flashlamp-pumped Nd:YAG amplifier for the first time, to the best of the knowledge, yielding a combined pulse energy of 167 mJ.
Abstract: Divided-pulse amplification (DPA) has proven to be a valuable tool in scaling the peak power of diode-pumped ytterbium-doped amplifiers to beyond the single-pulse threshold for parasitic nonlinear effects. DPA enables the amplification of picosecond pulses in solid-state amplifiers with limited bandwidth beyond the single-pulse damage threshold. In this Letter, we demonstrate DPA of picosecond pulses in a flashlamp-pumped Nd:YAG amplifier for the first time, to the best of our knowledge, yielding a combined pulse energy of 167 mJ.
7 citations
TL;DR: In this article, Tm:fiber and Ho-fiber lasers are in-band pumped using the same experimental setup to directly compare their performance as 2-micron sources.
Abstract: Thulium and holmium have become the rare earth dopants of choice for generating 2 micron laser light in silica fiber. The majority of Tm:fiber lasers are pumped with high power diodes at 790nm and rely upon cross-relaxation processes to achieve optical-to-optical efficiencies of 55-65%. Tm:fiber lasers can also be pumped at 90%. Ho:fiber lasers are similarly pumped by Tm:fiber lasers at 1900-1950nm, with <70% typical efficiency. In this work, Tm:fiber and Ho:fiber lasers are in-band pumped using the same experimental setup to directly compare their performance as 2 micron sources.
4 citations
27 Jun 2016
TL;DR: Experimental studies of laser induced filament propagation through atmospheric conditions have been done to understand the interaction of filaments with its propagating medium as they propagate at different pressures and through aerosols as discussed by the authors.
Abstract: Experimental studies of laser induced filament propagation through atmospheric conditions have been done to understand the interaction of filaments with its propagating medium as they propagate at different pressures and through aerosols.
2 citations
05 Sep 2016
TL;DR: In this article, a mid-IR supercontinuum spanning over 1-3.2 µm is generated through pumping highly nonlinear robust chalcogenide glass nanotapers with femtosecond pulses at 2 µm.
Abstract: A mid-IR supercontinuum spanning over 1-3.2 µm is generated through pumping highly nonlinear robust chalcogenide glass nanotapers with femtosecond pulses at 2 µm. Nanotapers are produced from a multimaterial high-index-contrast step-index fiber.
1 citations
30 Oct 2016
TL;DR: In this article, active and passive coherent pulse addition in a flashlamp-pumped Nd:YAG amplifier chain for pumping OPCPA systems was demonstrated with a 79% combination efficiency.
Abstract: We demonstrate active and passive coherent pulse addition in a flashlamp-pumped Nd:YAG amplifier chain for pumping OPCPA systems. The amplification of 200 ps pulses to 216 mJ is achieved with a 79% combination efficiency.
TL;DR: In this paper, the authors discuss the use of such integrated devices to stretch a 100 fs pulse to 400 ps with customized third order dispersion for use in a multi-TW Ti:Sapphire system as well as integrated optics to control the pulse duration in pump lasers for OPCPA systems.
Abstract: Pulse stretchers are critical components in chirped pulse amplification (CPA) and optical parametric CPA (OPCPA) laser systems. In CPA systems, pulse stretching and compression is typical accomplished using bulk diffraction gratings; however integrated devices such volume or fiber Bragg gratings can provide similar optical performance with significantly smaller footprint and simplified alignment. In this work, we discuss the use of such integrated devices to stretch a 100 fs pulse to 400 ps with customized third order dispersion for use in a multi-TW Ti:Sapphire system as well as integrated optics to control the pulse duration in pump lasers for OPCPA systems.
05 Jun 2016
TL;DR: In this article, the impact of Gaussian and annular beams on thermal lensing is experimentally tested by characterizing the propagation of 2 μm light in BK7, and the effect of annular beam for high power propagation is discussed.
Abstract: The impact of Gaussian and annular beams on thermal lensing is experimentally tested by characterizing the propagation of 2 μm light in BK7. The effect of annular beams for high power propagation is discussed.
05 Jun 2016
TL;DR: In this paper, mode selective amplification in a LMA cladding pumped Yb-doped fiber amplifier employing a photonic lantern is demonstrated with high mode fidelity with up to 19 dB and > 1W output power.
Abstract: We demonstrate mode selective amplification in a LMA cladding pumped Yb-doped fiber amplifier employing a photonic lantern. Signal gains of up to 19 dB and >1W output power are demonstrated with high mode fidelity.