ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
An apparatus for observing the IR multiple-photon resonances of jet-cooled polyatomic molecules using the optothermal technique is described. For experiments in the spectral region 9/11 μm, a commercially available, high-pressure CO2 laser with an improved wave number resolution (∼0.05 cm−1) is used as the pulsed radiation source. Although a moderate pumping capacity is available, high intensity, supersonic beam pulses are obtained by an expressly developed nozzle source. A superconducting bolometer with a responsivity of ∼2×104 V/W and an effective time constant of (approximately-equal-to)60 ns (for radiation) has been developed to detect the energy flux carried by the irradiated molecular beam. The time-resolved detector signal is then passed through an analogic processor which separates the fast, small amplitude component generated by the irradiated molecules from the larger component due to the unexcited beam. After further amplification, the useful signal is digitized and stored in a computer to be averaged over several repetitions and then time integrated. A detector input NEP of ∼1.5×10−12 W/(Hz)1/2 is obtained in a single laser pulse. This figure can be further reduced by averaging. Complementary information such as the laser fluence, the intensity of the molecular beam pulse, the optoacoustic signal from a reference gas, as well as the time-of-flight of the molecules can be simultaneously monitored. Part I of this article gives a general description of the apparatus, while Part II gives a detailed description of the bolometer and the related electronics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1141192
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