Masamori Endo

Azimuthally polarized 1 kW CO2 laser with a triple-axicon retroreflector optical resonator

An optical resonator for generating high-power, axially symmetric polarized beams is demonstrated. The rear mirror of a commercial CO(2) laser is replaced by a triple-axicon retroreflector unit that is composed of a waxicon and an axicon accurately fitted together. The selection of the polarization is made by the reflectivity difference between p and s polarizations at the inclined surfaces. Sharp discrimination of polarization within a 0.4% of difference in reflectivity is demonstrated. A stable 1 kW azimuthally polarized LG01 laser beam is generated, and the measured beam quality is 2.0.

Numerical simulation of an optical resonator for generation of a doughnut-like laser beam

A design of an optical resonator for generation of a doughnutlike laser beam in the far field is proposed. The resonator consists of a toric mirror, a flat output coupler, and a w-axicon with a movable center axicon. Two-dimensional vector electric field simulation has shown that any one of the Laguerre-Gaussian modes can be selected by sliding the center axicon. Therefore this resonator is capable of generating doughnut-like laser beams, whose dark spot size can be controlled in real time. This feature of the proposed resonator is advantageous for atom trapping and optical tweezers.

High-efficiency operation of chemical oxygen-iodine laser using nitrogen as buffer gas

High-efficiency operation of supersonic chemical oxygen-iodine laser (COIL) with an advanced jet-type singlet oxygen generator using nitrogen as buffer gas was demonstrated. Laser output was remarkably increased when buffer gas was cooled with liquid nitrogen. The effects of buffer gas temperature on the characteristics of the oxygen-iodine laser medium was discussed. A net chemical efficiency of 23.4% was obtained at 405 W when the chlorine molar flow rate was 19 mmol/s.

Output Power Enhancement of a Chemical Oxygen-Iodine Laser by Predissociated Iodine Injection.

Output power enhancement of a chemical oxygen-iodine laser (COIL) by an injection of predissociated iodine was studied. Iodine molecules were dissociated into atoms by the microwave discharge prior to injection. It was determined that predissociation caused a negative effect on the output power enhancement when this technique was applied to a conventional supersonic COIL. Model calculations revealed that the existence of atomic iodine at the plenum caused the dissipation of stored energy. It was demonstrated that decreasing the mixing point pressure was crucial to obtain output power enhancement by the predissociation technique. For this purpose, a low-pressure transonic mixing scheme with a grid nozzle array was developed. A 9% enhancement of output power was demonstrated.

Two-dimensional simulation of an unstable resonator with a stable core

An optical resonator simulation code based on the idea of a partially coherent optical field has been developed and used to optimize the design parameters of an unstable resonator with a stable core. The resonator was intended for use with low-gain, large-bore lasers, such as the chemical oxygen-iodine laser (COIL). First the design parameters of the resonator were optimized by the simulation code; then a set of mirrors was fabricated for a small-scale COIL. A 14-W output with M(2) = 29 was obtained. The experimentally obtained results were in good agreement with calculations.

High-efficiency chemical oxygen–iodine laser using a streamwise vortex generator

A supersonic expansion nozzle has allowed us to achieve highly efficient operation of the supersonic mixing chemical oxygen–iodine laser (COIL). The nozzle’s shape produced a rapid mixing of the primary and secondary flows. Made up of a series of thin alternating wedges placed adjacent to each other, the nozzle looks like the letter X when it is viewed from the side. Iodine is injected at the exit plane of the nozzle and is strongly entrained by the streamwise vortices generated by the nozzle. 599 W of output power with a chemical efficiency of 32.9% is obtained, values higher by a factor of 1.4 than those of the conventional COIL.

Performance Characteristics of Narrow Linewidth Fiber Laser Pumped Mid-IR Difference Frequency Mixing Light Source for Methane Detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

Numerical simulation of the w-axicon type optical resonator for coaxial slab CO2 lasers

The numerical simulation of the optical resonator for a coaxial slab CO2 laser is conducted. The resonator consists of a toric mirror, a w-axicon, and a plane output coupler. To hold the two slabs coaxially, struts exist in the annular gap region. The effects of the struts on the output power and beam quality for the given resonator are discussed. It is found that varying the vertex of the toric mirror can control the oscillation mode between the E00 fundamental mode and the E01 first azimuthal mode. It is revealed that the resonator loss of the fundamental mode can be smaller than the first azimuthal mode by shifting the vertex inward, and this results in single-mode oscillation at the E00 fundamental mode. On the other hand, the maximum output is obtained under conditions where the resonator oscillates at the E01 mode, because the nodes of the mode coincide with the position of the struts. Loss measurement of each eigenmode well describes the aforementioned phenomena.

Parametric studies of a supersonic COIL with angular jet singlet oxygen generator

Chemical oxygen-iodine laser (COIL) having a wavelength of 1.315 μm has been developed using a singlet oxygen generator (SOG) with a novel approach. Generated singlet oxygen is taken out of the SOG at an angle of 40° to avoid the problem of carry over of droplets, which is one of the major drawbacks of horizontal systems. The system has been operated using uncooled nitrogen as a buffer gas. The paper reports the results on the studies carried out on this COIL system. Under optimum conditions, we have been able to achieve stable and reproducible output power of 350 W for a chlorine flow rate of 22 mmol/s thus yielding a chemical efficiency of 17.5%.

Supersonic COIL with angular jet singlet oxygen generator

Abstract Supersonic Chemical Oxy-iodine Laser has been developed using a Singlet Oxygen Generator (SOG) with a novel approach. Generated singlet oxygen is taken out of the SOG at an angle of 40° to avoid the problem of carry over of droplets, which is one of the major drawbacks of horizontal system. The system has been operated up to 22 mmol/s chlorine flow rates. Chlorine utilization and singlet oxygen observed have been more than 90% and 60%, respectively. The observed maximum output power was 350 W , thus yielding a chemical efficiency of 17.5%.