We report on experimental evaluation of laser gain and q-switched output pulse energy in vicinity of 2-microns in Tm:Lu2O3 ceramic rod end-pumped by 796-nm diodes. Also included is Comparative test evaluation of upconversion effects in Tm:Lu2O3, Tm:YLF, and Tm:YAG materials. Wide-band tunable 2 µm Tm:Lu2O3 laser is sought for remote sensing, eye–safe lasers, laser processing of transparent plastics, medical therapy, ultra¬fast lasers (UFL), accelera¬tion of nuclear particles, and generation of visible output via harmonic conversion.
We have previously shown that the ceramic Yb:YAG-based edge-pumped disk laser amplifier offers significant advantages over traditional face-pumped disk amplifiers. Such amplifiers may be used in laser drivers for inertial confinement fusion, laser acceleration, and other applications, which require a combination of high-pulse energy and high-average power. Unlike face pumping, the edge-pumping architecture beneficially allows for reduced Yb doping and enables a construction of very simple, compact, and completely modular amplifiers comprising identical and interchangeable gain modules. This paper reports on the development and early testing of a Ø5-cm aperture edge-pumped ceramic Yb:YAG disk amplifier module pumped by 100-kW diodes at up to 20 Hz and cooled by a high-velocity gas flow at near ambient temperature. In early testing, the amplifier module has demonstrated very uniform transverse gain and 37 J of stored energy. A laser oscillator operating in a quasi-cw mode with 1- ms pump pulses produced 43 kW of instantaneous laser power and 31 J of energy at a wavelength of 1029 nm. Experimental results compare well to model predictions.
Wide-band tunable 2 µm lasers are sought for remote sensing, eye–safe lasers, laser processing of transparent plastics, medical therapy, ultra¬fast lasers (UFL), accelera¬tion of nuclear particles, and generation of visible output via harmonic conversion [1]. We have previously reported efficient lasing in Tm:Lu2O3 ceramic while tuning over 230-nm range in the vicinity of 2 µm and delivering up to 43 W QCW [2]. Tm:Lu2O3 ceramic gain material has a much lower saturation fluence than the traditionally used Tm:YLF and Tm:YAG materials, thus offering improved energy extraction. Ceramic construction offers size scalability and convenient fabrication of gain medium composites.
This paper reports on experimental evaluation of laser gain and q-switched output pulse energy in vicinity of 2-microns in Tm:Lu2O3 ceramic rod end-pumped by 796-nm diodes. Also included is the operation and spectral gain evaluation of a Tm:Lu2O3 ceramic edge-pumped disk laser with multi-passed extraction, which is seeded by the above end-pumped rod laser. This work was supported by the U.S. Department of Energy grant number DE-SC0013762.
1. Drew A. Copeland, John Vetrovec, and Amar S. Litt, "Wide-Bandwidth Ceramic Tm:Lu2O3 Amplifier," SPIE 9834, (2016).
2. John Vetrovec, et al., "2-Micron Lasing in Tm:Lu2O3 Ceramic: Initial Operation," SPIE vol. 10511 (2018)
We report on initial lasing of Tm:Lu2O3 ceramic laser with tunable output in the vicinity of 2 μm. Tm:Lu2O3 ceramic gain materials offer a much lower saturation fluence than the traditionally used Tm:YLF and Tm:YAG materials. The gain element is pumped by 796 nm diodes via a "2-for-1" crossrelaxation energy transfer mechanism, which enables high efficiency. The high thermal conductivity of the Lu2O3 host (~18% higher than YAG) in combination with low quantum defect of ~20% supports operation at high-average power. Konoshima’s ceramic fabrication process overcomes the scalability limits of single crystal sesquioxides. Tm:Lu2O3 offers wide-bandwidth amplification of ultrashort pulses in a chirped-pulse amplification (CPA) system. A laser oscillator was continuously tuned over a 230 nm range from 1890 to 2120 nm while delivering up to 43W QCW output with up to 37% efficiency. This device is intended for initial testing and later seeding of a multi-pass edge-pumped disk amplifier now being developed by Aqwest which uses composite Tm:Lu2O3 disk gain elements.
We report on testing of an edge-pumped ceramic Yb:YAG disk laser having a tailored spatial gain profile for preferential amplification of the TEM00 mode. The disk has a composite construction with a Yb-doped large-aperture central portion cosintered with an undoped perimetral edge. Light from multi-kW diodes is transported though the disk edge and absorbed in the Yb-doped center. This configuration makes it poss¬ible to conveniently arrange the diode light and produce a spatially flat gain profile, such as is desir¬able for the amplification of a spatial flat top beam or a tailored gain profile [1]. Amplified spontan¬eous emis¬sion (ASE) and parasitic lasing is mitigated by the geometry of the laser disk edge, which is designed to efficiently outcouple laser fluorescence [2].
This work experimentally investigated the tailored spatial gain profile and the lasing performance of TEM00 mode (Gaussian spatial profile) beam without the distorting effects of gain saturation. Compari¬son of the lasing performance of a flat spatial gain to that with tailored gain is presented. This work was supported in-part by the US Department of Energy grants DE-SC0013762 and DE-SC0015834.
1. Drew A. Copeland and John Vetrovec, “Gain Tailoring Model and Improved Optical Extraction
in CW Edge–Pumped Disk Amplifiers,” SPIE Vol. 8235, 82350U (2012).
2. John Vetrovec, Drew A. Copeland, Amardeep S. Litt, Suraj J. Thiagarajan, and Eldridge Briscoe "Stored Energy and Gain in an Edge-Pumped Ceramic Yb:YAG Disk Laser under Intense Pumping," SPIE Vol. 10084, 1008407 (2017).
We report on testing of an edge-pumped ceramic Yb:YAG disk laser for pulse amplification under intense pumping. The disk has a composite construction with Yb-doped central portion cosintered with an undoped perimetral edge. Light from multi-kW pulsed diodes is transported though the disk edge and absorbed in the Yb-doped center. This configuration results in a very simple and compact laser gain module. The disk is operated as a storage amplifier. Amplified spontaneous emission and parasitic lasing is alleviated by the geometry of the laser disk edge rather than absorption cladding. Our test results indicate that this approach offers a robust mitigation of ASE. This work presents results of stored energy, gain, and ASE mitigation in the Yb:YAG disk laser under intense pumping.
We report on the investigation of a novel ceramic Tm:Lu2O3 amplifier lasing at around 2-μm and offering efficient generation of high-energy pulses with high-peak power at high repletion rate, high efficiency, and with near-diffraction-limited beam quality (BQ). The amplifier has a bandwidth of over 300 nm, which offers broad tunability. The bandwidth also supports generation of ultrashort pulses in the femtosecond regime. The “2-for-1” pump architecture of the Tm ion enables high optical-to-optical efficiency while pumping at around 800 nm. High thermal conductivity of the Lu2O3 host supports operation at high-average power. The ceramic nature of the Lu2O3 host overcomes the scalability limits of single crystal sesquioxides.
A remote atmospheric breakdown (RAB) is a very rich source of ultraviolet (UV) and broadband visible light that could provide the early warning to the presence of CW/BW agents through spectroscopic detection, identification and quantification at extended standoff distances. A low-intensity negatively chirped laser pulse propagating in air compresses in time due to linear group velocity dispersion and focuses transversely due to non-linear effects resulting in rapid laser intensity increase and ionization near the focal region that can be located kilometers away from the laser system. Proof of principle laboratory experiments are being performed at the Naval Research Laboratory on the generation of RAB and the spectroscopic detection of mock BW agents. We have demonstrated pulse compression and focusing up to 105 meters in the laboratory using femtosecond pulses generated by a high power Ti:Sapphire laser. We observed nonlinear modifications to the temporal frequency chirp of the laser pulse and their effects on the laser compression and the positions of the final focus. We have generated third harmonics at 267 nm and white light in air from the compressed pulse. We have observed fluorescence emission from albumin aerosols as they were illuminated by the compressed femtosecond laser pulse.
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