Iwao Ogura

Photorefractive effect in GaP

The photorefractive effect in undoped semi-insulating GaP was observed. GaP has a photorefractive sensitivity in the spectral region of 0.6 to 0.9 microm. The photorefractive center is the deep donor resulting from the P antisite defect. We measured the two-beam coupling gain coefficient and its time constant as functions of the grating period and the pumping intensity, using a 633-nm He-Ne laser. The maximum gain coefficient of 0.33 cm(-1) was obtained at a grating period of 1.1 microm. The time constant, which depends on the grating period, was 3-20 msec at a pumping intensity of 30 mW/cm(2).

Second harmonic generation of a copper vapor laser in barium borate

Abstract The beam from a copper vapor laser with an unstable resonator was focused in a nonlinear crystal, barium borate, for second harmonic generation. Ultraviolet light of 255.3 nm was generated with an conversion efficiency of 8.9% at an average input power of 2.55 W. The characteristics of conversion were investigated.

Measurement of spatial coherence of a copper vapour laser beam using a reversal shear interferometer

We measured the spatial coherernce of a copper vapour laser (CVL) beam with an unstable resonator by the reversal shear interferometer. By this method, we can evaluate the spatial coherence function from a single-shot measurement. The spatial coherence width was 5 mm when an unstable resonator with a magnification factor of 60 was used. Moreover we verified the result by the theoretical calculation on the basis of the passive resonator model.

Experimental verification of nonreciprocal response in light scattering from rough surfaces

The so-called reciprocity law that the response is not different when a light source replaces a detector (or vice versa) on a scattering surface has been examined experimentally for scattered light from a ground glass surface. The result shows that the reciprocity law is not strictly fulfilled. We call this phenomenon a nonreciprocal response in light scattering from rough surfaces. Measurements were taken with a goniometer in the domain where the scattering and incident angles are from 15 to 90°. As the ground glass surface becomes rougher, the response curve of the scattered light deviates further from the reciprocity law.

Non-collinear interaction model of the second harmonic generation of a copper vapor laser

Abstract We estimated theoretically the conversion efficiency of the second harmonic generation of a copper vapor laser (CVL) beam. Since the CVL beam is only partially coherent, the theory for the coherent beam is useless for the second harmonic generation of the CVL beam. The focused CVL beam was considered as a set of bundles of rays with propagated in different directions through a crystal and non-collinear interaction between these bundles of rays was investigated. On the basis of this model, we found that the conversion efficiency depends on the product of the beam divergence and the beam diameter, and the length of a nonlinear crystal.

Laser-induced damage threshold and absorption measurements in rare-gas-halide excimer laser components

Abstract We have developed a new system to measure the damage threshold with high reproducibility. We controlled the total energy on the sample by an optical system, without changing a spot-size on the sample surface. We made high-reflection coatings with and without over-coat, and anti-reflection coatings with and without under-coat for 248 nm KrF excimer laser light. In high-reflection coating, non-quarter-wavelength design was also tested. Damage threshold of coatings for 193 nm ArF excimer laser were also tested. We measured the absorption of coatings by the interferometric laser calorimetry. Revealing a cause of damage, we made a qualitative and quantitative analysis, so that the main cause of the damageof the optical coatings for 248 nm light was the residual absorption of the coatings.

Parametric Study On The Second Harmonic Generation Of A Copper Vapor Laser

To obtain an efficient and high-repetition rate ultraviolet light, the 2553 nm second harmonic of a copper vapor laser was generated in barium borate, the excellent nonlinear crystal in ultraviolet region. High quality laser beam from an unstable resonator was focused in the crystal to achieve high power density. The conversion efficiency of 9 % was obtained at an average input power of 2.5W.

Time-resolved measurement of beam divergence of a copper vapor laser using a saturable absorber

Abstract We measured the temporal change of the beam divergence of a copper vapor laser using the saturable absorber DASBTI. The recovery time of the absorption of the DASBTI (∽ 50 ps) is much shorter than the temporal change of the intensity of the copper vapor laser (∽ 20 ns). In this case, the transmissivity is a linear function of the instantaneous intensity. The beam divergence can be derived from the input and output power.

Absorption measurements of laser optical materials by interferometric calorimetry

The widespread use of high‐power lasers requires further studies of the very low loss materials. The development of such materials has led to the progress in the measurement technique of small absorption coefficients. We propose a new technique of measuring bulk and surface absorption coefficients using an interferometric calorimetry. It is important to separate surface absorption from bulk absorption, for recent studies have revealed that surface damage occurs earlier than bulk damage. The sample exposed to a laser beam absorbs the light proportional to its absorption coefficient. Change in optical path arises because the index of refraction and the sample thickness depends on temperature. We can obtain the bulk and the surface absorption coefficients by measuring this change of optical path length by using the Michelson interferometer or the holographic interferometer.

Linewidth measurement and population calculation of a He‐Cd laser

The radiative linewidth and pressure broadening of Cdii 4416‐A transition have been found to be 56±6 MHz and 8.7±2.9 MHz/Torr from the Lamb dip in a single‐mode He‐Cd laser. The population densities of the He metastables and Cd upper laser levels and the small‐signal gains of the Cdii 4416‐ and 3250‐A transitions are calculated under the various conditoins of a positive column He‐Cd laser through the rate diagram involving most of the important collisional and radiative processes. The calculated results are in trhe fair agreement with the experiments reported by other authors. The saturation of the laser output with an increasing discharge current can be explained by the rapid increase of stepwise excitation from the He metastable and the comparatively slow decrease of the electron temperature. Based on the measured linewidth and