Minoru Kimura

Optical distortion of transmissive optics at high power CO 2 laser irradiation

The optical distortions of transmissive optics for high power CO(2) lasers have been measured by the interference of a probe He-Ne laser beam. The change of interference fringes is observed by a video camera when the sample is irradiated by a cw high power CO(2) laser. From the change of fringe pattern, the optical distortion is obtained and the spatial distribution of the temperature rise is derived. Thermal expansion and thermal change of the optics cause optical distortions. Both factors have to be added to large thermal lensing effects for ZnSe optics but they are small for KCI optics.

Microwave-discharge-excited CO2 laser using orthogonal electric fields

We have developed a high-power microwave discharge excited carbon-dioxide laser oscillator by using a newly developed method called the orthogonal electric fields method in which the vibration direction of an electric field changes over time for achievement of a homogeneously spread electric discharge. A homogeneously spread electric discharge with a high output power and a high laser efficiency has been generated. The relative discharge area of the electric discharge accounted for about 70% of the cross section of the laser tube. In the configuration of a single discharge area, we achieved a maximum laser output power of 273 W at 1450 W microwave input power, and a a maximum laser efficiency of 20.2% at 1070 W microwave input power. At the maximum laser output power, the input power density was high, at about 240 W/cm3, which is about 20 times that achieved using a dc discharge method. Furthermore, a demonstration model having five electric discharge areas in a laser tube showed a maximum laser output power of 609 W at 3590 W microwave input power, and a maximum laser efficiency of 22.7% at 1394 W microwave input power. This work demonstrates the possibility of fabrication of a high-power microwave discharge excited carbon-dioxide laser which could be widely used industrially.

CO2 laser radar 3D vision sensor for a mobile robot

The laser radar proposed in this paper has good performance as a vision sensor for disaster prevention robots. Due to the good transparency of the CO2 laser, the range information through simulated...

Heterodyne interferometer of coaxial CO2 and He–Ne lasers for plasma density measurements

An interferometer using coaxial CO2 and He–Ne lasers has been developed for electron density measurements in the reversed field pinch plasma. The interferometer uses the phase modulating heterodyne detection of 60 MHz. The CO2 laser interferometer is free from the mechanical vibrations due to the reduction of the vibrations by the air springs and the compensation of the vibrations by the He–Ne laser interferometer. The electron density measurement during a long‐time discharge of 50 ms without the disturbance by the vibrations is achievable. The resolution is less than 1/100 fringe of the CO2 laser interferometer, therefore the electron line density as small as 1.1×1014 electrons/cm2 is detectable.

Powerful single‐frequency CO2 laser for plasma diagnostics

A cw 240‐W CO2 laser has been developed for plasma scattering measurements. The laser oscillates only on the 10P(20) transition (10.5912‐μm wavelength) at a single longitudinal as well as transverse mode with linear polarization. These properties are obtained by using an adequately long cavity with a folded beam configuration. Part of the output beam was heterodyned with a local oscillator laser to confirm the single‐frequency oscillation. The short‐term frequency stability was 200 kHz (7×10−9) for an observation time of 1/15 s. The shift of the oscillating frequency due to the discharge current was 360 kHz/mA and the frequency shift due to the total gas pressure was 4.1 MHz/Torr. These frequency shifts are mostly attributable to the change of the refractive index of the laser gas.

Pulsed CO2 laser oscillator excited by microwaves

The optimum excitation conditions for pulsed CO2 laser oscillation excited by microwaves are investigated to achieve oscillation with a short pulse width at a high repetition rate. The excitation conditions are optimized as follows; (1) by evaluating the decay time of excited N2 molecule population density to optimize the gas mixture, and (2) by evaluating the discharge stability and the laser output waveform to optimize the magnetron drive conditions. We have developed a new coaxial fast gas flow pulsed CO2 laser oscillator excited by microwaves, which produces pulses output with a rise time of less than 5 microsecond(s) ec rise-time and a 1/e- fall time of 30 microsecond(s) ec at a maximum repetition rate of 5 kHz. It is also possible to modulate the output power and the pulse waveform at high speed. The oscillator is currently being tested for application to a laser drilling system for printed wired boards.

Visual sensing and range measurement by scanning of carbon dioxide laser

A laser vision sensor has been developed to enable range measurement and identification of targets through flames, smoke, and fog which are invisible to the human eye. This vision sensor employs a 10.6 micrometers -wavelength carbon dioxide laser for its long wavelength. The target is scanned two-dimensionally by the laser beam, directed by a pair of galvanometer mirrors, to produce the target image and measure the range of the target. The laser beam, amplitude-modulated to 5 MHz with an electro-optic modulator, is projected onto a target, and the reflected beam is detected by a cadmium mercury telluride detector. The phase difference between the projected and reflected light signals is used to provide range data up to 30 m. The indoor test is carried out with a 1 cubic meter box in which flames, smoke, and fog can be generated. The laser beam is projected through this box, and the targets behind this box are detected. The reproduced image is sufficient for identification through flames, smoke, and fog.