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  • 1
    Publication Date: 2011-08-17
    Description: Absolute line-center frequencies for eleven lines of ammonia in near coincidence with CO2-laser transitions have been determined to accuracies of + or -3 MHz by infrared heterodyne detection. These results were obtained by heterodyning a blackbody with a stable grating-tuned CO2 gas laser. A discussion of the apparatus and method of calculation, including error analysis, is presented. With these accurately determined line-center positions, the ammonia molecule will be a useful secondary-frequency standard for diode-laser spectroscopy in the 11-micron wavelength region.
    Keywords: LASERS AND MASERS
    Type: Optics Letters; 1; Sept
    Format: text
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  • 2
    Publication Date: 2016-06-07
    Description: The optical design considerations for optimization of sensitivity, tunability, and versatility of an infrared heterodyne spectrometer are discussed using the GSFC CO2 laser heterodyne spectrometer optical front end as an example. Problems related to the coherent nature of the laser local oscillator beam (e.g., interference effects at edges of optical elements and at the beam combining beamsplitter) are described and proper beamsplitter design discussed. Optimum matching to the telescope is discussed. The severe effects of large central obscuration on the coherent telescope efficiency are described and steps to partially recover the lost system sensitivity are proposed. Measurements made with the GSFC 48 inch telescope (linear obscuration rate = 0.5) and the KPNO McMathe telescope (no obscuration) are given as examples.
    Keywords: LASERS AND MASERS
    Type: NASA. Langley Res. Center Heterodyne Systems and Technol., Pt. 2; p 365-372
    Format: application/pdf
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  • 3
    Publication Date: 2016-06-07
    Description: A diode laser based IR heterodyne spectrometer for laboratory and field use was developed for high efficiency operation between 7.5 and 8.5 microns. The local oscillator is a PbSSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed cycle cooler. The laser output frequency is controlled and stabilized using a high precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Single laser modes are selected by a grating placed in the local oscillator beam. The system employs reflecting optics throughout to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. Spectral analysis of the diode laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the infrared spectral regions over which useful heterodyne operation can be achieved. System performance has been studied by making heterodyne measurements of etalon fringes and several Freon 13 (CF3Cl) absorption lines against a laboratory blackbody source. Preliminary field tests have also been performed using the Sun as a source.
    Keywords: LASERS AND MASERS
    Type: NASA. Langley Res. Center Heterodyne Systems and Technol., Pt. 1 p199-208 (SEE N80-29652 20-36)
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  • 4
    Publication Date: 2019-06-28
    Description: Fully resolved intensity profiles of various lines in the CO2 bands at 9.4 micrometers and 10.4 micrometers were measured on Mars using an infrared heterodyne spectrometer. Analysis of the line shapes shows that the Mars atmosphere exhibits positive gain on these lines, providing the first definite detection of natural optical gain amplification and enabling identification of these lines as the first definite natural laser ever discovered.
    Keywords: LASERS AND MASERS
    Type: NASA-TM-82048
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