Tatehisa Ohta

High-Resolution Temperature Measurement Using Phase-Compensating Interferometer and Frequency-Monitoring Interferometer

A noncontact interferometric thermometry method based on phase-compensating interferometry is described. Direct frequency monitoring by the reference interferometer connected in parallel to the sensing interferometer provides temperature measurement of high accuracy.

Magnetic Field Tuning Dips in He–CdII and He–ZnII Hollow Cathode Lasers

The decay rates of the upper laser levels of He–CdII and He–ZnII lasers have been measured utilizing the magnetic field tuning dip, and the variations of these decay rates with He pressure are studied. The spontaneous decay rates of CdII and ZnII are estimated from the zero pressure intercept and found to be 58.1 MHz (4f2F7/2°, CdII, the upper level of 5378 A), 1.24 MHz (5s22D5/2, CdII, 4416 A), and 97.3 MHz (4f2F7/2°, ZnII, 4924 A). The variation of the decay rate of the upper laser level with metal source temperature is also studied with a He–CdII 4416 A hollow cathode laser and the difference of this variation between hollow cathode and capillary discharge lasers is discussed.

Frequency stabilization of 633-nm He-Ne laser by using frequency modulation spectroscopy of127I2 enhanced by an external optical cavity

The oscillation line from a two-mode stabilized inner-mirror-type 633-nm He-Ne laser was locked to the iodine saturated absorption line. FM spectroscopy was used to detect the saturated absorption signal. An iodine cell was placed within the ring cavity to multiply the excited light. When the oscillation line on the red side (long-wavelength side) of the two-mode stabilized laser was locked to the 6-3 band P(33) transition a-component of 127I2/ the degree of frequency stabilization measured from the Allan variance σ(2, τ) was 2.3 × 10−11 × τ−1/2 on either the red or blue side. Under this condition, the nonmodulated optical power on the blue side was 1.3 mW. In addition, the dependence of the frequency shift of the P(33) transition a-component on iodine vapor pressure and the frequency separations of oscillations for a to j components were measured.

Frequency stability improvement of a two-mode stabilized 633-nm He–Ne laser

The red side (lower-frequency) mode of a two-mode stabilized 633-nm He-Ne laser has been locked to the hyperfine structure of the P() line of (127)I(2) by means of frequency modulation spectroscopy enhanced by an external optical cavity. Both the red side and blue side (higher-frequency) modes of the laser exhibit a frequency stability of 2.3 x 10(-11) tau(-1/2). In addition, the frequency fluctuations of the blue side mode are detected by a Fabry-Perot cavity and compensated through an acousto-optic frequency shifter. The short-term stability of better than 3 x 10(-11) is attained for integration times of between 2 x 10(-3) and 2 x 10(-1) s.

Anomalous broadening spectra due to isotope effects in the high-power He-CdII white light lasers

It has been recognized that since the He-CdII lasers are usually operated under considerably high buffer-gas pressure, the oscillation modes in these lasers can automatically reduced by their homogeneous broadening mechanism due to the high buffer-gas pressure. Therefore, it has been expected that the oscillation scheme in these lasers can easily be single-moded when they are operated in high power. We have examined this fact with a most high-power (100mW) He-CdII white light laser which has just come to be commercially available in Japan. As a result, this is true only in the cases of the 537.8 nm and 636.Onm lines, but in the case of the 441.6nm lines an anomalous broadening of the spectral width, which amounts to as much as more than 2GHz has been measured. This degrades the coherence length of this blue line less than 15cm. Such a large broadening can be attributed to the isotopes involved in the natural cadmium metal used for the laser material.

De-excitation in Electronic Collision Process in Gas Lasers

The laser action produces changes of population in the upper and lower levels involved. These population changes lead to the light intensity changes of spontaneous emission originating from the upper and lower levels, ΔI52 and ΔI21, respectively. The ratio of these intensity changes, ΔI21/ΔI52, is theoretically calculated. By analysing the experimental data of this ratio observed on 6328A emission in a He-Ne laser, the probabilities of de-excitation by electronic collision of the upper 3s2 and lower 2p4 levels, P52e and P21e, respectively, are obtained. The value of probability P52e at a discharge current of 30 mA for a laser tube of 3.5 mm diameter is (3.4±0.6)×107 sec-1 and is of the same order as the total probability of radiative transition of 3s2 level, A52. The total cross section of this electronic collision process σ52e is estimated to be (6.8±1.2)×10-13 cm2. The value of P21e at 30 mA is much smaller than the value of the probability of 2p4 level, A21. This technique also yeilds the ratio of A52/A521 to be 2.1±0.8, where A521 is the probability of radiative transition from 3s2 level to 2p4 level.

Optical polarization switching and bistability by injected light in a 633 nm He- Ne laser

Many researches have been done in the field of free-space optical interconnection due to the inherent parallelism and large bandwidth of optics. Packaged planar optical system seems to be promising to realize the rigid and compact interconnection modules for inter and intra-multichip module interconnections.’,’ However, stringent alignment accuracy requirement may lead to a complicated packaging pro~ess .~ In this report, we present that the alignment accuracy requirement can be reduced by using the focused Gaussian beams compared with the one-to-one imaging. We investigate the effect of misalignment in the micro optical system4 used for a space-variant free-space interconnection as shown in Fig. 1. We assume a Gaussian beam profile throughout the optical system. The maximum interconnection length L, is given as a function of beam radii at two lenses, wz and

Unique Polarization Caused by Frequency Locking between σ and π Modes in a Transverse Zeeman Laser

Experiments on polarization characteristics of a single-longitudinal-mode internal-mirror 633 nm He-Ne laser with very small cavity anisotropy have been performed. A polarization rotating phenomenon from the σ to the π mode direction and to directions other than the σ or π direction by varying magnetic field strength (2.7 to 9.0 mT) has been observed. Here, polarization is independent of the natural axis, and this rotated polarization switches alternately between adjacent longitudinal modes with respect to the σ mode axis. These alternating polarizations are not perpendicular to each other. The rotation and the switching of polarization are unique. Furthermore, we have conducted theoretical analyses on polarization characteristics under the strong coupling condition of σ and π modes based on the theory of the transverse Zeeman laser. Then it is concluded that this unique polarization rotation is caused by the frequency locking of the two modes.

Internal-mirror He-Ne laser stabilized to saturated absorption of iodine in an external ring resonator

Saturated absorption of iodine was observed using the polarization-stabilized internal-mirror He-Ne laser. An external ring resonator was used to enhanced saturated absorption. The P(33) line provided a sufficient signal to noise ratio for laser frequency stabilization.

New scheme of digital optical switching and memory operation utilizing the mode-hopping phenomenon in semiconductor lasers

A new scheme of digital optical switching, optical analog-to-digital conversion, and wavelength bistability is presented which can be applied to digital optical, memory operations, utilizing the mode-hopping phenomenon of Fabry-Perot cavity-type injection laser diode. The measured speed of switching was within the nsec region, which was limited by the driving capabilities and the light detection response, not by the phenomenon itself.