Sze Tan

Applications of cavity ring-down spectroscopy to high precision isotope ratio measurement of 13C/12C in carbon dioxide

Recent measurements of carbon isotopes in carbon dioxide using near-infrared, diode-laser-based cavity ring-down spectroscopy (CRDS) are presented. The CRDS system achieved good precision, often better than 0.2‰, for 4% CO2 concentrations, and also achieved 0.15–0.25‰ precision in a 78 min measurement time with cryotrap-based pre-concentration of ambient CO2 concentrations (360 ppmv). These results were obtained with a CRDS system possessing a data rate of 40 ring-downs per second and a loss measurement of 4.0 × 10−11 cm−1 Hz−1/2. Subsequently, the measurement time has been reduced to under 10 min. This standard of performance would enable a variety of high concentration (3–10%) isotopic measurements, such as medical human breath analysis or animal breath experiments. The extension of this ring-down to the 2 μm region would enable isotopic analysis at ambient concentrations, which, combined with the small size, robust design, and potential for frequent measurements at a remote site, make CRDS technology attractive for remote atmospheric measurement applications.

Portable low power cavity ring-down spectrometer for precise measurement of carbon dioxide, methane and water vapor

The necessity for monitoring of changing levels of greenhouse gases (GHGs) is clearly evident now more than ever. This has led to large deployments of analytical devices to most remote locations as well as the most densely populated regions around the world. Both large and small scale projects have forced new and old technologies to be pushed to their limits to obtain the highest performing measurements while maintaining a cost effective way to remotely monitor changes in atmospheric concentrations. In order to accomplish these strict guidelines, we present a low-power cavity ring-down spectrometer that measures Carbon Dioxide, Methane and water vapor which can achieve measurements with precisions lower than 20ppb of CO2 and 50ppt of CH4. Comparing to hundreds of watts needed in conventional CRDS design, we demonstrate that the high performance can be achieved with less than 25W. Stability of these measurements has allowed for averaging times of up to 3hr, yielding measurements of methane concentrations with precisions down to 40ppt. This is accomplished utilizing an FSR based frequency scale to determine an absolute frequency scale for these absorption features. Taking advantage of this faster, and less costly measurement technique of CRDS shows future promise with applications spanning scientific and industrial analyses, from isotopes to trace gases.

Multi-Species Gas Detection and Precise Line Area Measurements Using CRDS and a High-Precision Wavemeter

We demonstrate precise measurement of absorption line width made possible with a high-precision wavelength monitor, enabling the determination of species concentration from the line area. We also demonstrate simultaneous measurement of multiple species concentrations.

Novel external CW frequency doubling of semiconductor lasers to generate 488 nm

We report a simple and compact all-solid-state laser generating 488 nm light with continuously variable output power in the range from 1 mW to over 120 mW. We frequency double single frequency radiation from an external cavity semiconductor laser in a periodically poled MgO:LiNbO3 ridge waveguide. The laser maintains a high quality TEM00 circular beam with M2 < 1.1 and very low r.m.s. noise of less than 0.06% over the entire range of output power. Less than 0.1% peak-to-peak output power variation was measured during 14 hours of operation. No degradation of the conversion efficiency has been observed for operation at an output power of 70 mW for 3.5 months. The prototype laser has a small footprint of 5x8 cm.