English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

presented. The two experiments discussed herein have been motivated by the growing need of compact all-solid-state CW sources in the 3 to 18 ƒÊm wavelength range. This range contains strong fundamental molecular absorption bands of many organic and inorganic air pollutants, and can be used for real-time sensitive measurement of these pollutants in situ and over long path. Lead-salt diode based trace gas detection in the mid-infrared have been recently demonstrated by Webster et al [ 1], and can be used as an alternative to near-infrared overtone detection [2]. Lead-salt diode lasers, however, require cooling with liquid nitrogen for normal operation which may be a practical drawback. An alternative to lead-salt diodes are multiple-quantum-well antimonide diode lasers [3]. Their performance characteristics such as operating temperature, spectral purity, and output power, have dramatically improved in recent years. Further research and development in this area can potentially result in simple and reliable single-frequency CW sources in the 3 to 5 ƒÊm region with tens of milliwatts of output power, operated at room or thermoelectric temperatures. Another important technique for generation of tunable infrared light are continuous-wave OPO [4] and DFG [5]. The DFG pumped by near-infrared semiconductor lasers [6-8], in our opinion, offers a clear advantage of stable single longitudinal mode operation, good amplitude and frequency stability, and wide continuous tuning range. To investigate the applicability of DFG to trace gas detection, we have built and tested two tunable infrared sources: one near 3.2 for the detection of methane, the other near 4.6 ƒÊm for the detection of carbon monoxide and nitrous oxide. Schematic diagrams of these sources are shown in Figure 1. The 3.2 ƒÊm source was pumped by two different compact lasers: a 500 mW diode-pumped monolithic Nd:YAG ring laser at 1064 nm (signal), and a 20 mW extended-cavity diode laser (ECDL) at 800 nm (pump). In later experiments, the ECDL was replaced with a 100 mW solitary Fabry-Perot diode laser in order to increase the IR output power and allow fast wavelength modulation. The lasers were mixed in a 5.5 mm antireflection-coated AgGaS2 placed inside a bow-tie enhancement cavity. The cavity was locked to resonance at 1064 nm to increase effective signal power available for mixing. The long arm of the cavity was not a conventional bow-tie in that a Littrow prism reflector was used instead of a flat mirror. The function of this element was to eliminate multiple passes of the 800 nm light in the cavity. Use of a flat mirror resulted in a small portion of the diode laser light circulating in the cavity which produced a systematic ripple in the IR power when the diode was tuned. The bow-tie cavity design with the addition of a Littrow prism reflector provides several advantages: it employs a minimum number of intracavity elements, is easy to align, has flexible mode diameter control, which is important for reaching optimum DFG conversion efficiency, and eliminates cavity resonance at the pump wavelength. The source was scanned by sweeping the frequency of the ECDL or solitary laser diode. The 3.2 ƒÊm output beam (idler) was monitored using two room-temperature InAs detectors. A maximum of 6 ƒÊ W IR power was measured with 40 mW pump power incident on the crystal, and 230 mW signal power in front of the cavity, which corresponds to 3.75 W intracavity signal power. Operation with more than 4.2 W intracavity Nd:YAG power was achieved, accompanied by noticeable thermal lensing in the mixing crystal. Frequency tuning of the idler wave was performed by tuning of the pump laser and crystal angle. At a fixed phase matching angle, frequency tuning over a range of approximately 10 cm-1 was possible, due to small crystal length. Therefore, short frequency scans of 10 GHz for spectroscopic measurements did not require crystal rotation. Tuning of the pump laser

RECENT ADVANCES IN TUNABLE MID-INFRARED LASER SOURCES FOR ENVIRONMENTAL GAS MONITORING