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  • 07.65.-b  (1)
  • 33.60  (1)
  • 1
    ISSN: 1432-0649
    Keywords: 07.65.-b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low-wavelength modulation (1 kHz), high-wavelength modulation (100 MHz) and two-tone frequency modulation (390±5 MHz) spectroscopies are systematically compared by measuring the minimum detectable absorption achieved using an AlGaAs diode laser tuned on a third-overtone methane transition at 886 nm. From the S/N behavior has been extrapolated a minimum relative absorption (1 Hz of bandwidth) of 4.5(1)×10−7 for the LMW, 9.7(3)×10−8 for the HWM and 6.4(2)×10−8 for the TTFM. In the LWM case the detection-limit value is represented by the laser amplitude 1/f excess noise, while for the high-frequency detection techniques this contribution is negligible with respect to other noise sources. These detection limits well agree with the calculated “quantum limited” values based on measured laser power, modulation index, noise figure of the electronic components, and other parameters of the apparatus.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 42.55H ; 33.60 ; 06.30F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The operation of a cw FIR laser in the presence of a strong electric field is described. A hybrid metal-dielectric waveguide is used and the cavity length is scanned to study how the frequency and power of the laser depend on the field strength. The results have also been checked by heterodyning with a conventional reference laser. We report the results obtained for the 496 μm line of CH3F and the 70.5 μm and 119 μm lines of CH3OH. A large frequency tunability of almost ±40 MHz is obtained in the best case with power levels in the mW range. A very simple theoretical model accounts for the experimental results. We also report the appearance of a new FIR line at about 204 μm when CH3OH is pumped by the 9 μmP(34) of CO2 in the presence of an electric field larger than 1.2 KV/cm.
    Type of Medium: Electronic Resource
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