Frequency stabilization of a GaAIAs semiconductor laser by voltage control.

A single-mode GaAlAs laser is frequency stabilized by keeping the injection current and the voltage across the laser constant. A long-term frequency stability of 7 x 10(-8) and a reproducibility of 3 x 10(-7) were obtained.

Stationary Fourier-transform spectrometer.

The performance and the characteristics of an interferometric double-mirror spectrometer with uncollimated light are studied by measuring spectra of different radiation sources. The stationary interferometer is fabricated without a beam splitter or moving components. The measured interferogram visibilities, which are limited by the size of the source aperture, agree with the theoretical predictions for a slit and a circular source aperture. By background subtraction the effect of detection nonuniformity can be radically reduced to increase the dynamics and the resolving power of the spectrometer. We used a mercury pencil lamp for measurement and found that the dynamic range was ~80 dBm. When isolated spectral lines are measured, the resolving power can be improved by squeezing more than half of a spatial interference cycle onto one pixel. The maximum resolving power reached in measuring the spectra of a diode laser was 1600. The instrument is applicable to a wide range of measurements, such as the recording of temporally variant, wideband radiation sources and the monitoring of laser wavelength.

Polarization-stabilized 1.15- and 3.39-microm He-Ne lasers.

Two methods for polarization stabilization of an internal-mirror 3.39-microm He-Ne laser are reported. The first relies on a concurrently lasing 1.15-microm transition by fixing the relative amplitude of two orthogonally polarized longitudinal modes that are split by a Rochon prism and detected with separate Si photodiodes. In the second method, two spatially separated orthogonally polarized adjacent 3.39-microm modes are optically balanced, differentially chopped, and recombined on a single InSb photodiode for phase-sensitive detection. The dual-wavelength scheme has been tested by beating against a methane-stabilized 3.39-microm He-Ne laser, which yields maximum excursions of < 0.5 MHz over several hours and comparable reproducibility. The polarization-stabilized He-Ne laser has been used as a reference for a tunable color-center laser molecular-beam optothermal spectrometer and provides a precision of better than 2 MHz.

Laser wavelength measurement with a Fourier transform wavemeter.

We report results from spectral measurements in the optical and near infrared region performed with a Fourier transform wavemeter. Characteristics of a variety of lasers and the performance of the wavemeter have been studied. The group of cw lasers measured in this work is comprised of a 1550-nm multimode diode laser, an 820-nm single-mode diode laser, a 594.5 nm dye laser, and He-Ne lasers at wavelengths of 1523, 633, and 543 nm. The Fourier transform wavemeter is powerful in multimode laser investigations and in long-term frequency stability determinations. The measurements show that the wavemeter also easily reveals very low power laser modes; it is suitable for the investigation of the single-mode purity of lasers. The line position uncertainty <10(-8) can be concluded in the measurements with polarization-stabilized 633- and 543-nm He-Ne lasers.

Comparison of the behavior of stainless and mild steel manual metal arc welding fumes in rat lung.

The lung retention and clearance of manual metal arc (MMA) stainless steel and mild steel welding fumes were determined in the rat. The exposure simulated the actual welding situation. The duration of exposure in the "nose-only" exposure chamber was 1 h/workday for one, two, three, or four weeks in the retention study and for four weeks in the clearance study. The concentration of exogenous iron was determined by the magnetic measuring method. Instrumental neutron activation analysis was applied to determine the concentration of total iron, chromium, and nickel in the lungs. The results indicated that the lung retention and clearance patterns for the two types of welding fumes were different. A linear relationship was observed between the amount of stainless steel MMA welding fume retained in the lungs and the duration of exposure, whereas the retention of mild steel MMA welding fume in the lung was saturated as a function of the cumulative exposure time rates. The maximum amount of lung-retained contaminants was 880 micrograms for stainless steel MMA welding fume and 220 micrograms for mild steel MMA fume.

Evaluation of biological monitoring among stainless steel welders.

Ten manual metal arc (MMA) high alloy stainless steel (SS) welders were studied during one week and the concentrations of chromium (Cr) and nickel (Ni) were determined in their urine and blood. Stationary and personal air samples were collected from the immediate work environment; they covered the entire work period. Spot urine samples were collected during the follow-up period. Whole blood and plasma samples were taken from the workers before and after one shift, and the retention rate of magnetic dust in the lungs was estimated with magnetopneumography. On the basis of the results, indices of short-term exposure to Cr and Ni were evaluated. Urinary Cr and Ni concentrations (corrected to creatinine) reflect both the body burden caused by long-term and short-term exposure to easily soluble fractions of these metals. The results indicated that the use of Cr and Ni urinary analyses as indices of short-term exposure is not as dependable as previously assumed. The Cr and Ni concentrations in whole blood and plasma did not correlate with the measured exposure, but the daily mean increase in the Cr concentration reflected exposure to total Cr and Cr(VI) very well. The large variation in the Cr concentration of the morning urine (0.01-2.7 mumol/1) and blood (0.05-1.43 mumol/1) indicated large personal variations of body burden among the exposed welders. The retention rate of magnetic dust in the lungs correlated well (P less than 0.01) with the daily mean increase of Cr in blood. Very good correlations (P less than 0.001) were found between the retention rate of magnetic dust and the personal air samples of Cr and Cr(VI).