Yasuhiro Tokita

Power stabilization of hollow cathode He−Cd+ white light laser

The laser power stabilization of the hollow cathode He–Cd+ white light laser was studied. The power stabilization must be projected for three color lights; red, green, and blue, because the white light laser is composed of the three color lights. The laser output variation is mostly caused by Cd vapor pressure and input power. Then to reduce the variation, the authors proposed three techniques: the inclusive anode power control technique, the individual anode power control technique, and the light feedback control technique and compared them to each other. The feedback technique has realized the best output stability: the short-time output power variations (fluctuations) in red, green, and blue obtained by the experiment were 0.32%, 0.18%, and 0.32%, respectively.

Gain Characteristics of Hollow Cathode He-Cd+ White Light Laser

The hollow cathode He-Cd+ white-light laser simultaneously oscillates at three primary colors of light (red, green, and blue) in the visual range. The red output has wavelengths of 636.0 nm and 635.5 nm; the green output has wavelengths of 537.8 nm and 533.7 nm; and the blue output has a wavelength of 441.6 nm. The authors measured the small signal gains of these five wavelengths using an amplifier method. The three color outputs radiated from the oscillator tube were directed into an amplifier tube in order to measure the dependence of the gain coefficient on the anode current and the He pressure for each wavelength.

High–power HeCd+ white light laser

The hollow cathode HeCd+ laser includes twelve oscillation lines. The oscillation line of 441.6 nm (blue), 533.7 nm and 537.8 nm (green), and 635.5 nm and 636 nm (red) in the visible area can be oscillated concurrently by using wide-band mirrors for a resonator to produce a white light laser. This laser is expected particularly in the image production industry because a single laser tube allows the three primary colors of light to be produced and the green wavelengths are optimum for green emulsion of photographic films. However, it has been difficult to produce the hollow cathode HeCd+ laser of continuous oscillation and high power. We have investigated the high power and output stability of the white light laser for practical purposes. As a result of examining the structure of the hollow cathode as a means for high-power laser, we could realize a high-power HeCd+ white light laser by using a new structure which was an improvement over the conventional flute type. This paper explains the structure of the hollow cathode and shows the dependencies of the output on the Cd vapor pressure, He pressure, input power for the cathode length of 61 or 43 cm, and the noise characteristics for the cathode length of 61 cm.

Photoconductive Plastic Holography Employing White-Light Laser.

We have succeeded in quasi real-time holography engineering by using a photoconductive plastic (PCP) plate and in full-color holography engineering by employing a hollow-cathode type, He?Cd+, white-light laser. We have also succeeded in eliminating ghost images, which are inherent in holograms reconstructed from multiwavelength light, using diffused reference illumination.

Experimental Studies on Longitudinal Mode Characteristics of a Hollow Cathode He–Cd+ White Light Laser

A hollow cathode CW He–Cd+ white light laser can oscillate simultaneously at three primary colors (five transitions) in a single tube. The frequency characteristics are important parameters in many applications. Therefore, we have investigated the longitudinal mode of our white light laser. In our experiment, we have found that the red and green transitions oscillate in a single longitudinal mode in spite of a wide gain profile and that the blue transition oscillates in a few longitudinal modes. We consider that this single-mode operation can be caused by hole burning due to mode competition between the longitudinal modes and the saturation coupling. Furthermore, we measured the pressure broadenings and the natural linewidths of the five transitions upon changing of the He gas pressure in the He–Cd+ white light laser.

Characteristics of 325-nm CW Oscillation of a Hollow Cathode He–Cd + Laser

A hollow-cathode He-Cd+ laser oscillates with 12 lines. The oscillation line at 325 nm could emit only by pulse oscillation using the conventional hollow cathode. The 325 nm line is promising in the measurement and chemical analysis fields. Simultaneous oscillation of both the line at 325 nm and one or more lines in the visible light range are desired as well. The authors utilized the hollow-cathode He-Cd+ laser of 61 cm in cathode length used for high-power white light laser oscillation to enable 325-nm single-light oscillation to be emitted continuously with a power of 18 mW.

Multi-Wavelength Holographic Interferometry Using the White-Light Laser

The interferogram of an inclined plate illuminated by a white-light laser was obtained by computer simulation and experiment. In the simulation, the interference fringe is related to the displacement of the object. We verify some advantages of multi-wavelength holographic interferometry over the conventional holographic interferometers which use a single wavelength. We also show some limitations of the detectable displacement range for practical measurement. In the simulation, color variations of the interferogram are related to the displacement of the object. In the experiment, we obtained an interference fringe that has almost the same appearance as the simulated one.