A Diode Pumped Middle Infrared Laser Based on Ho: GdVO4 Crystal

Ho: GdVO4 crystal is the host material for the production of laser working in the middle infrared range. In this contribution, the characteristic parameters of the Ho: GdVO4 crystal were measured, and the material was used as a gain medium to build a diode-pumped laser for the first time, to reach a laser output at 2047.9 nm. The output beam quality factor M2 was measured to be 1.4 and 1.3 in x-direction and y-direction, respectively. In addition, the influence of the transmittance of the output mirror on the generation of laser was obtained through exploration. The results showed that the laser wavelength blue-shifted as the output transmittance increased.

Seven-rod pumping approach for the most efficient production of TEM00-mode solar laser power by a Fresnel lens

A seven-rod/seven-TEM00 mode beam Fresnel lens solar laser pumping approach is here proposed. The Fresnel lens with 4.0 m2 collection area was used as the primary solar concentrator to pump seven 2.5 mm diameter, 15 mm length Nd:YAG rods within a conical pump cavity through a secondary fused silica aspheric concentrator. Within the pump cavity, solar pump rays not completely absorbed by one of the seven rods were furtherly absorbed by other rods, ensuring hence a high absorption efficiency and avoiding the serious thermal lensing and thermal stress issues associated with classical large rod solar lasers. Seven individual plane-concave large-mode resonators were adopted to enable a good overlap between solar pump mode and TEM00 laser oscillating mode. By using both ZEMAX® and LASCAD® software, the maximum total TEM00 mode solar laser power of 54.65 W was numerically calculated by optimizing the radius parameter of the Fresnel lens, the diameter of the laser rod and the radius of curvature of the laser resonator output mirror. 13.66 W/m2 TEM00 mode solar laser collection efficiency and 1.44% solar power-to-TEM00 mode laser power conversion efficiency were calculated, representing substantial enhancements of 4.66 times and 4.38 times, respectively, as compared to previous experimental records of the TEM00 mode solar laser pumped through a Fresnel lens with 0.785 m2 collection area. The feasibility of TEM00 mode solar laser power delivery by hollow-core photonic crystal fibers was finally studied.

Employment of gradient metal-film output mirrors in terahertz discharge lasers

Subject and Purpose. The problem of output beam matching with the waveguide transmission line often arises when using terahertz lasers. The special quasi-optical devices that are used to combat the problem lead to radiation losses and additional material costs. The aim of this work is to develop appropriate output mirrors for THz lasers so as to make the output laser beam match the transmission line of a given diameter. Methods and Methodology. As part of the experimental research into the action of the output mirror configuration on the parameters of THz laser radiation, gradient metal-film mirrors are made like a transparent substrate with a thin metal layer on it. The layer thickness varies over the substrate surface, forming therewith a transparency spot with a given change in the transmittance in the middle of the mirror. The properties of the gradient metal-film output mirrors are examined as applied to a gas-discharge HCN laser at a wavelength of 337 μm. Results. The gradient metal-film mirrors enable obtaining laser beams of a diameter equal to the inner diameter of the relevant transmission line and with a proper transverse energy distribution. The efficiency of the transmission of laser radiation energy into the waveguide line increases, and so does the performance of the laser installation. Another positive point is that the enhanced transparency in the middle of the mirror raises efficiency of the active substance energy utilization and conveys focusing properties to the flat mirror, which reduces diffraction losses. Conclusions. The employment of gradient metal-film output mirrors makes it possible to raise efficiency of laser installations. The features of metal-film mirrors suggest broad potentials for their application and make reasonable their further research.

Анализ внутренних оптических потерь вертикально-излучающего лазера спектрального диапазона 1.3 μm с туннельным переходом на основе слоев n-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InAlGaAs

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n++-InGaAs/р++-InGaAs/р++-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20°С and 90°С, respectively.

Theoretical Investigation of Near-Infrared Fabry–Pérot Microcavity Graphene/Silicon Schottky Photodetectors Based on Double Silicon on Insulator Substrates

In this work a new concept of silicon resonant cavity enhanced photodetector working at 1550 nm has been theoretically investigated. The absorption mechanism is based on the internal photoemission effect through a graphene/silicon Schottky junction incorporated into a silicon-based Fabry–Pérot optical microcavity whose input mirror is constituted by a double silicon-on-insulator substrate. As output mirror we have investigated two options: a distributed Bragg reflector constituted by some periods of silicon nitride/hydrogenated amorphous silicon and a metallic gold reflector. In addition, we have investigated and compared two configurations: one where the current is collected in the transverse direction with respect to the direction of the incident light, the other where it is collected in the longitudinal direction. We show that while the former configuration is characterized by a better responsivity, spectral selectivity and noise equivalent power, the latter configuration is superior in terms of bandwidth and responsivity × bandwidth product. Our results show responsivity of 0.24 A/W, bandwidth in GHz regime, noise equivalent power of 0.6 nW/cm√Hz and full with at half maximum of 8.5 nm. The whole structure has been designed to be compatible with silicon technology.

Demonstration of polarization control GaN-based micro-cavity lasers using a rigid high-contrast grating reflector

We reported on GaN microcavity (MC) lasers combined with one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. The HCG structure was directly fabricated on the GaN structure without an airgap. The entire MC structure comprised a bottom dielectric distributed Bragg reflector; a GaN cavity; and a top HCG reflector, which was designed to yield high reflectance for transverse magnetic (TM)- or transverse electric (TE)-polarized light. The MC device revealed an operation threshold of approximately 0.79 MW/cm2 when pulsed optical pumping was conducted using the HCG structure at room temperature. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14° (full width at half maximum). This laser operation demonstration for the GaN-based MC structure employing an HCG exhibited the advantages of HCGs in semiconductor lasers at wavelengths from green to ultraviolet.

Online Measurement of Internal Parameters in a Quasi-CW Diode-Pumped Nd:YAG Laser

We present a simple and practical online measurement method to estimate internal parameters (small-signal gain coefficient, internal optical losses, the saturation parameter, and transmittance of the coupling output mirror) in an neodymium doped yttrium aluminum garnet Nd:YAG laser system. A measurement cell, placed in the optical cavity of a laser, consists of a polarizer and a rotatable polarization analyzer. Internal parameters are measured conveniently by introducing variable polarization reflective loss. Online measurements of the internal parameters in a quasi-continuous-wave (CW) diode-pumped Nd:YAG laser are performed and the measured results, which are discussed and analyzed, indicate good measurement accuracy. Experiments to investigate validity are conducted and further verify the applicability of the measurement method. A measurement cell with a small volume that is easy to access has potential to be used in the online measurement, optimized design, and maintenance of a laser.