We demonstrated that transverse mode can be controlled by manipulating gain distribution in a Yb:YAG ceramic thin disk. Several elongated higher order transverse modes of a Hermite-Gaussian beam were observed when a straight-line-shaped gain region was created by using a diode laser output from an optical fiber. An orthogonally crossing pair of straight-line-shaped gain regions created with an additional optical fiber output resulted in the generation of a doughnut-shaped Laguerre-Gaussian beam. This implies that easy and quick switching of Hermite-Gaussian and Laguerre-Gaussian beams is possible without mechanical handling.
A portable
chemical analysis system for monitoring ambient carbonyl
sulfide (COS) was investigated for the first time. COS is paid attention
to from the perspectives of photosynthesis tracer, breath diagnosis
marker, and new process-use in the manufacture of semiconductors.
Recently, the threshold level value of COS was settled at 5 ppm in
volume ratio (ppmv) for workplace safety management. In this work,
COS was converted to H
2
S by a small column packed with
alumina catalyzer at 65 °C. Then, the H
2
S produced
was collected in a small channel scrubber to react with fluorescein
mercuric acetate (FMA), and the resulting fluorescence quenching was
monitored using an LED/photodiode-based miniature detector. The miniature
channel scrubber was re-examined to determine its robustness and easy
fabrication, and conditions of the catalyzer were optimized. When
the FMA concentration used was 1 μM, the limit of detection
and dynamic range, which were both proportional to the FMA concentration,
were 0.07 and 25 ppbv, respectively. Ambient COS in the background
level and even contaminated COS in the nitrogen gas cylinder could
be detected. If necessary, H
2
S was removed selectively
by reproducible adsorbent columns. COS concentrations of engine exhaust
were measured by the proposed method and by cryo-trap-gas chromatography-flame
photometric detection, and the results obtained (0.5–5.9 ppbv)
by the two methods agreed well (
R
2
= 0.945,
n
= 19). COS in ambient air and exhaust gases was successfully
measured without any batchwise pretreatment.
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