CO₂laser stabilized on narrow saturated absorption resonances of CO₂, improved absolute frequency measurements

Abstract

We have stabiliz ed a CO2 laser on narrow saturated absorption resonances of CO2 detected on the transmitted beam of an external Fabry-P Â erot cavity in the 30 THz spectral region. By using another CO2 laser stabilized on a close OsO4 line whose absolute frequency is precisely known, and measuring the beat frequency with a precision of 100 Hz, we determined the absolute frequency of twenty CO2 laser lines, with uncertainties between 100 Hz and 1 kHz mainly limited by the accuracy of the OsO4 grid. This set of measurements reveals some discrepancies with data based on measurements performed with the widely used saturated ¯uorescence technique; we attrib ute these to pressure shifts of several kilohertz under the conditions of this last m ethod.

Absolute frequency measurement of 12C16O2 laser lines with a femtosecond laser comb and new determination of the 12C16O2 molecular constants and frequency grid

“…3 displays the relative Allan deviation of the stabilized CO 2 laser, as calculated from the absolute frequency measurement (see Section 3). It is 6.2 · 10 À13 s À1/2 between 1 and 100 s, a factor 3 better than the previous measurements [12]. This progress is related to the better signal-to-noise ratio of the reference line.…”

“…Finally, for three transitions in the 10 lm region, the frequency of a laser stabilized with the saturated fluorescence technique was measured by connection to the OsO 4 grid, which permitted to evaluate the pressure shift [14]. All these results showed that a new calibration of the CO 2 grid is needed, as already pointed in [12] and [14].…”

“…An uncertainty of 50 Hz was obtained on the R(10) line at 10 lm by connection to the OsO 4 grid [11]. Together with the P(12) and P (14) measurements, these data were included in the calculation of Maki. In 1997, 20 absolute frequencies of 12 C 16 O 2 laser lines around 10 lm were determined with accuracies between 100 Hz and 1 kHz [12]. For this purpose, the laser was stabilized on the molecular signal detected in transmission of a Fabry-Perot cavity [13].…”

“…Second, this reference generated from a H-maser itself controlled with the TAI (International atomic time) at BNM-SYRTE (Paris Observatory) was transferred through a 43-km optical fiber to our laboratory with a negligible degradation of the spectral properties [15]. Using these frequencies and previous measurements at 10 lm [8,11,12] we determined with an improved accuracy the rotational constants for the three vibrational levels implied in the transitions. Finally a new calculation of the frequency grid for the normal CO 2 isotopomer was performed.…”

Optoelectronic difference-frequency synthesiser: terahertz-waves for high-resolution spectroscopy

“…Unfortunately, the calibration of the difference-frequency is strongly affected by the systematic frequency shifts of the locked laser. They should be responsible for the significant value observed (626(14) kHz) of the zero-frequency intercept in the linear regression of ν T Hz + δν HF − 2f AOM1 against n. An electronic compensation of the offset of the error signal, as done in [17], in the servo loop of the diode lasers would improve the difference-frequency accuracy.…”