Yasuharu Mine

Room-temperature mid-infrared laser sensor for trace gas detection

Design and operation of a compact, portable, room-temperature mid-infrared gas sensor is reported. The sensor is based on continuous-wave difference-frequency generation (DFG) in bulk periodically poled lithium niobate at 4.6 mum, pumped by a solitary GaAlAs diode laser at 865 nm and a diode-pumped monolithic ring Nd:YAG laser at 1064.5 nm. The instrument was used for detection of CO in air at atmospheric pressure with 1 ppb precision (parts in 10(9), by mole fraction) and 0.6% accuracy for a signal averaging time of 10 s. It employed a compact multipass absorption cell with a 18-m path length and a thermoelectrically cooled HgCdTe detector. Precision was limited by residual interference fringes arising from scattering in the multipass cell. This is the first demonstration of a portable high-precision gas sensor based on diode-pumped DFG at room temperature. The use of an external-cavity diode laser can provide a tuning range of 700 cm(-1) and allow the detection of several trace gases, including N(2) O, CO(2), SO(2), H(2) CO, and CH(4).

A New Kinetic Model for Assessing the Performance of Advanced CO2 Gasdynamic Lasers

A theoretical analysis of CO2 gasdynamic laser ( CO2-GDL) performance using a six-temperature model is described in this paper. This model has specifically included vibrational transfer processes associated with vibrational non equilibrium of O2 and H2O so that the kinetic behaviors of these species in an active laser medium can be properly assessed. The calculation carried out with this model showed that presence of O2 in the laser medium together with H2O reduces the population inversion. Consequently, under the condition where the concentration of H2O was ~4 mol%, every additional percent of O2 was found to be about one percent reduction in the small signal gain of a CO2-GDL. The calculation resulted in good agreement with experimental studies in the variation of the small signal gains as well as vibrational temperatures for various laser gas composition.

Characteristics of a downstream-mixing CO 2 gasdynamic laser caused by behavior of two supersonic flows in a laser cavity

A combustion-driven downstream-mixing CO(2) gasdynamic laser (GDL) is developed. When the total mass flow rate is ~ 2 kg/s and the combustion gas temperature is 1750 K, a small-signal gain coefficient of up to 0.6% cm(-1) and a laser output power as high as 11 kW are measured. To explain the experimental values, a mixing loss factor was previously introduced into an analytical model incorporating the three-temperature kinetics model. In the present study, a numerial analysis and further experiments are carried out to clarify the mixing behavior of two supersonic flows in the laser cavity. A measuring method for the average static temperature in the laser resonator is adapted, and it is made clear that, with the current state of supersonic nozzle manufacturing technology, two supersonic flows will not mix well.

Numerical analysis of O2 and H2O effects on CO2 gas dynamic lasers

A six-temperature vibrational relaxation model that takes into account the vibrational levels of O2 and H2O is proposed, based on which a simulation code has been developed with which analyses have been conducted on the effects brought on the performance of combustion- driven gasdynamic lasers by the presence of O2 and H2O in the medium. Inclusion of the vibrational levels of O2 and H2O in the vibrational relaxation model has proved to ensure good agreement of estimated results with experimental data over a wide range of gas composition (0 - 40% O2, 0 - 10% H2O). Both calculation and experiment have indicated that with the presence of 3% H2O, an increase of 1% in O2 concentration would lower the small signal gain by 1%. The simulation estimated that increasing concentration of H2O in the laser medium accentuates the effect of O2 on the lasing performance. This six-temperature vibrational relaxation model should permit reliable analysis to be performed on gasdynamic laser characteristics even when large amounts of O2 and H2O are present in the medium.

Japanese CELRAP laser radar: obstacle warning avoidance function

The obstacle warning avoidance function of the Japanese CELRAP laser radar system is verified based on the return signal measurements using wires as targets under various conditions. The system applicability for the function is successfully confirmed.

Novel multifunction 2-μm imaging laser radar system

A novel imaging laser radar system using a Tm, Ho:YLF laser, applicable for multi-function such as obstacle warning avoidance, range finding, range mapping and target profiling was fabricated. The maximum field of view of the laser radar image produced with Palmer scanning is 12 degree(s) by 48 degree(s). A tower at 2,500 m was observed, demonstrating its capability for range finding function. Obstacle warning avoidance function and target profiling function was tested by taking the laser radar image of the wires and a car, respectively.

Phased array MOPA system using an adaptive mirror

Fundamental experiments using a phased array MOPA (master oscillator with power amplifier) system configuration, composed of the multi-dither COAT (coherent optical adaptive technique) system and two MOPA chains, were carried out to evaluate the validity of the COAT system in the MOPA configuration. It was shown experimentally that phase-locking of two carbon-dioxide laser beams in the MOPA configuration can be achieved by using the adaptive mirror of the multi-dither COAT system.

Potential study of CO2 gas dynamic laser using solid propellant

We investigated performance of a gasdynamic laser (GDL) with combustion gas of a double base propellant theoretically. Small signal gain coefficients in the supersonic flow of the combustion gas were calculated for different stagnation conditions characterized as the operation region of conventional GDLs. Preliminary experiments show that less solid particles exist in the combustion gas flow than we expected. It was revealed from theoretical and experimental results that a conventional GDL which uses the doubled base propellant as a gas generator could be realized.