A Gaussian pulse propagated through a multimode optical fiber is well explained by introducing a weighting function of higher order modes into the theoretical formula, being consistent with experimental results. Extending the equation of the pulse propagation in a single mode fiber into that for the multimode fiber, the calculated waveform with several weighting functions is compared with the experimental pulse of a He-Ne 3.39µm mode-locked laser, which propagated through As-S glass fiber. Cosequently, the most appropriate weighting function is found to be hyperbolic function W(l)l-0.7, which depends only on the radial mode l and is independent of the azimuthal mode m. Physical interpretation about the obtained weighting function is also discussed.

By analyzing reflectance variation of human blood involving various diseases under DC magnetic field at Ar+ 0.5 µm laser line, we can obtain new informations for diagnosis on whether the disease is malignant or benign.

Using an electrically controllable (EC) Echelette grating which consists of numerous thin glass-plates on a unimorph transducer, the wavelength selection and intracavity modulation are demonstrated at CO2 10.6 µm laser, together with the basic characteristics of the grating and theoretical treatments. Under intracavity setting of the grating in three-mirror configuration of a resonator, the initially oscillated CO2 line, P22, is typically moved into P18 line with 100V applied to the grating. On the intensity modulation, about 30% of modulation is also obtained with only 10 V.

An optical fiber-coupled type laser has been optimized by taking account of field disturbance on a coupling aperture mirror, and this has been examined by using conventional CO2 laser. Solving the eigen equations for a quasi-hemispherical resonator with a coupling aperture to find the field distribution on the plane mirror with an aperture, its effective transmittance is analytically evaluated as a function of normalized aperture ξ by the mirror size and is well approximated by the power series expansion up to the fourth order for various mirror Fresnel numbers N and the g parameter of resonator. Using this obtained and typical laser parameters for the experimental set to be used, the coupling aperture is optimized to yield the maximum power. As a result, the optimum aperture becomes a minimum at a specific g2 parameter of the concave mirror, i.e. g20.73, implying that the optimum configuration corresponds to be slightly off from a pure hemispherical setting. These theoretical estimates of the output power vs aperture have been compared with the experimental results obtained for a CO2 laser, being in qualitative agreements with each other in overall characteristics. By this optimization the maximum output power 6.0 W was extracted from the aperture of 2.4 mm.

Introducing temperature-dependent terms into the propagation constant and its derivatives, and extinction coefficient of a core material of optical fiber, the equation of pulse propagation in a multimode fiber is derived, allowing us to evaluate the temperature dependence of a pulse waveform such as the peak-intensity, the pulse duration or width and the pulse delay-time at the peak as a function of ambient temperature. Using the weighting function for higher order modes in the above equation, the theoretically calculated waveforms are compared with the mode-locked He-Ne 3.39 µm laser pulses propagated through As-S fiber over the range from room temperature to 220, being in good agreement each other.

Taking into account the higher order dispersions of the complex propagation constant involving its loss term, the equation of a Gaussian pulse propagation is derived for a single-mode optical fiber, by which the pulse-peak intensity, the pulse-width, the pulse-delay time and the skewness can be readily estimated along the fiber length. Then, among various combinations of the dispersion profile between the loss and the phase terms including both normal and anomalous dispersions, two typical cases of the pulse-broadening and narrowing are numerically shown, in which possibility of the compression is especially discussed with the combination of the sharp anomalous absorption-band and the normal phase-dispersions.

The Michelson-interferometer (MI) optical resonator has been applied, together with physical interests, to a low pressure and slow-flow type CO2 laser for specifying the system to a probe laser source. The fundamental characteristics online-selection, oscillation power and transverse mode are also investigated in comparison to the CO2 laser obtained for various resonators such as an open-ended reflective-multiple interferometer (RMI), an open-sided MI, a Fox-Smith interferometer and soon. Consequently, it is confirmedthat the MI type laser proposed can be one of the promising scheme, without losing oscillation power much and transverse mode quality as a probe laser towards lineshape (or laser) parameter analysis. Translating one of the MI mirror by a slight distance on the order of a micron meter along the gain axis, we can not only switch either a single rotational-vibrational line or combination of multiple lines, but also obtain different combination of lines by translating a large amount of the translation distance of the order of 100 µm. Moreover, elimination of one of the side-mirrors in the MI resonator enables us to switch the oscillation lines at the expense of some output power.

Use of a gold catalyst with cooling of the laser-tube wall results in enhancement of the output power in an open-cycle fast-axial flow CO2 laser. When Al2O3 spheres (diameter 3 mm) covered with numerous gold-catalyst hemispheres (40Å) on their surface were inserted within the gas-circulation loop, the total output increased by 16% from the open-cycle CW 500 W value to 580 W, with simultaneous cooling of the plasma-tube wall down to 30. The total oscillator power-increment was about 16%, in which 9% was enhanced with cooling the plasma wall and 7% was due to Au catalyst. From this slight modification without changing any physical configuration of setup and the gas composition, the oscillator output-power exceeding 700 W/m could be readily achieved in an open-cycle fast-axial flow laser. Taking into account both the catalytic contributions and the cooling effect of the plasma-tube wall on the population of the upper lasing level n2, thereby, the gain parameter G, and other laser parameters such as the saturation irradiance Is and the measure of homogeneity m, involving the dependences on both the gas-flow velocity v and the discharge current Idis, the oscillator output-power is theoretically calculated and compared with the experimental results, and good agreement is obtained.