Kazuhito Tanii

Undamped undulation superposed on the passive Q-switching pulse of a CO2 laser

An undamped undulation superposed on the pulse tail of the passive Q-switching is observed using HCOOH gas as a saturable absorber. The pulse shapes with the undulation are nicely reproduced through the rate-equation analysis in which the laser gain medium is described as a three-level system. Good agreements between the observation and the calculation are also obtained in the dependence of the period and the width of passive Q-switching pulse on laser parameters. The mechanism of the undulation is interpreted as the relaxation oscillation attributed to the relaxation from the lower laser level. The collisional rate constant of HCOOH molecule is also obtained.

Comprehensive interpretation of passive Q switching and optical bistability in a CO 2 laser with an intracavity saturable absorber

A CO2 laser with a saturable absorber shows passive Q switching or optical bistability, depending on the lasing conditions. These characteristics are theoretically analyzed on a comprehensive basis. The conditions under which passive Q switching or optical bistability occurs are investigated on phase diagrams by applying the linear stability analysis to the rate equations that describe the laser system. Exclusive occurrence resulting from the phase-diagram analysis is in good agreement with the present experimental results. The passive-Q-switching pulse with an undamped undulation is nicely reproduced through numerical integration of the rate equations.

Laser instability and chaotic pulsation in a CO 2 laser with intracavity saturable absorber

A CO2 laser with a gaseous saturable absorber shows a variety of periodic self-pulsation [passive Q switching (PQS)], depending on the lasing conditions and the characteristics of the absorbing molecules. We present a novel rate-equation model that comprehensively describes the transient pulse structures of PQS in the CO2 laser system. The numerical calculation based on the present model predicts that a chaotic PQS pulsation also is realized in a limited parameter region.

Sinusoidal self-modulation in the output of a CO 2 laser with an intracavity saturable absorber

Conditions under which a sinusoidally modulated laser output occurs in a CO2 laser with a saturable absorber were studied experimentally and theoretically for a wide range of laser operating parameters. A novel type of transition between stability and instability appears in the high-pressure range of the saturable absorber. Through the rate-equation analysis based on the three-level (the gain medium)–two-level (the loss medium) model, the observed pulse shapes and the features of transitions in the phase diagram are reproducible. The conditions of saturable absorbers to obtain the sinusoidal modulation are clarified from the analysis.

Intermittency route to chaos in a bimode CO/sub 2/ laser with a saturable absorber

damine6G solution in the microcavity was pumped by a pulsed dye laser at 510 nm with pump radius of about 10 pm. The input-output characteristics is illustrated in Fig. 1 where we have a jump of about lo3 in the output power at threshold. At the same time we have observed a jump in the degree of polarization of the emission from about 10% to 85%. Figure 2(a) and @) show the fluctuation of the peak output intensity below and above threshold, respectively. Below threshold, a Bose-Einstein-like distribution is obtained while above threshold a Poisson-like distribution is obtained. This intensity distribution is typical of a single-mode operation of a laser, and can not be obtained for a multimode operation even if each mode obeyed Bose-Einstein-like distribution. Thus we believe that we have attained a single-mode operation. Detailed experimental results on the pump-power dependences of the mode radius and spectral width will be reported.