F. R. Petersen

Accurate frequencies of molecular transitions used in laser stabilization: the 3.39‐μm transition in CH4 and the 9.33‐ and 10.18‐μm transitions in CO2

The frequencies of three lasers stabilized to molecular absorptions were measured with an infrared‐frequency synthesis chain extending upwards from the cesium frequency standard. The measured values are 29.442 483 315 (25) THz for the 10.18‐μm R(30) transition in CO2, 32.134 266 891 (24) THz for the 9.33‐μm R(10) transition in CO2, and 88.376 181 627 (50) THz for the 3.39‐μm P(7) transition in CH4. The frequency of methane, when multiplied by the measured wavelength reported in the following letter, yields 299 792 456.2(1.1) m/sec for the speed of light.

Tunable Far Infrared Spectroscopy

Tunable, cw, far‐infrared radiation has been generated by nonlinear mixing of radiation from two CO2 lasers in a metal‐insulator‐metal (MIM) diode. The FIR difference‐frequency power radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two‐tenths of a microwatt of FIR power was generated by 250 mW from each of the CO2 lasers. The combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotope lasers promises complete coverage of the entire far‐infrared band from 100 to 5000 GHz (3–200 cm−1) with stepwise‐tunable cw radiation. To demonstrate the usefulness of the technique, we observed the J=4–5 line of CO at 567 GHz.

Absolute frequency measurements of the 2-0 band of CO at 2.3 μm; Calibration standard frequencies from high resolution color center laser spectroscopy

Abstract The absolute frequencies of 20 lines of the 2-0 band of CO near 4260 cm −1 have been measured by heterodyne frequency measurement techniques. Eleven of the lines were measured by saturated absorption techniques which produced linewidths of about 3 MHz. New rovibrational constants have been fitted to these measurements. A table of calculated transition frequencies is given with estimated absolute uncertainties as small as 0.0000023 cm −1 (70 kHz) near the band center. The pressure shifts of three lines have been measured and fall in the range from −0.9 to −3 kHz/Pa (−122 to −400 kHz/Torr). It is suggested that the generally accepted frequencies of the 1-0 band of CO should be lowered by 7 MHz.

Direct frequency measurement of the I 2 -stabilized He–Ne 473-THz (633-nm) laser

The absolute frequency of the 473-THz He-Ne laser (633 nm), stabilized on the g or i hyperfine component of the (127)I(2) 11-5 R(127) transition, was measured by comparing its frequency with a known frequency synthesized by summing the radiation from three lasers in a He-Ne plasma. The three lasers were (1) the 88-THz CH(4)-stabilized He-Ne laser (3.39 microm), (2) a 125-THz color-center laser (2.39 microm) with its frequency referenced to the R(II)(26) (13)C(18)O(2)laser, and (3) the 260-THz He-Ne laser (1.15 microm) referenced to an I(2)-stabilized dye laser at 520 THz (576 nm). The measured frequencies are 473 612 340.492 and 473 612 214.789 MHz for the g and i hyperfine components, respectively, with a total uncertainty of 1.6 parts in 10(10). The frequency of the i component adjusted to the operating conditions recommended by the Bureau International des Poids et Mesures is 473 612 214.830 +/- 0.074 MHz.

Heterodyne frequency measurements on the 11.6-μm band of OCS: new frequency/wavelength calibration tables for 11.6- and 5.8-μm OCS bands

Heterodyne difference frequency measurements between a (13)CO(2) laser and a diode laser tuned (and in most cases locked) to the peaks of OCS absorption lines have been used to improve frequency calibration tables in the 860-cm(-1) region by factors of 20-50. Measurements have been made on the vibrational transitions 10(0)0-00(0)0, 11(1)0-01(1)0, and 20(0)0-10(0)0 for OCS. The measurements on the 10(0)0-00(0)0 and 20(0)0-10(0)0 transitions are also used to provide frequency calibration tables for the 20(0)0-00(0)0 band of OCS near 1700 cm(-1).

Direct frequency measurements of transitions at 520 THz (576 nm) in iodine and 260 THz (1.15 μm) in neon

The o hyperfine component of the (127)I(2) 17-1 P(62) transition at 520 THz (576 nm) in iodine was measured with respect to the CH(4)-stabilized 88-THz He-Ne laser. A 26-THz CO(2) laser, a color-center laser at 130 THz, and a He-Ne laser at 260 THz were used as transfer oscillators. The measured I(2) frequency was 520 206 808.547 MHz with a total fractional uncertainty of 1.6 x 10(-10). The 1.15-microm (20)Ne Lamb-dip-stabilized laser frequency was 260 103 249.26 MHz with a total fractional uncertainty of 3.1 x 10(-10).

Extension of absolute frequency measurements to 148 THz: Frequencies of the 2.0‐ and 3.5‐μm Xe laser

Absolute infrared frequency measurement has been extended to 148 THz (the highest frequency ever directly measured) with measurement of the two strong cw laser lines of Xe. The frequencies were synthesized with stabilized CO2 and 3.39‐μm He‐Ne lasers and mixed on a W‐Ni point‐contact diode. The measured frequencies are νXe(2.0μm)=147.915 850(15) THz and νXe(3.5μm)=85.459 997(3) THz.

Heterodyne frequency measurements of carbonyl sulfide transitions at 26 and 51 THz. Improved OCS, O13CS, and OC34S molecular constants

Abstract Heterodyne frequency measurements were made on selected absorption features of carbonyl sulfide (OCS) near 26 THz (860 cm−1) and 51 THz (1700 cm−1). Frequency differences were measured between a tunable diode laser (TDL) locked to carbonyl sulfide absorption lines and either a stabilized 13CO2 laser or a CO laser which was referred to stabilized CO2 lasers. These measurements are combined with conventional TDL measurements and published microwave measurements to obtain new, more reliable molecular constants for OCS, O13CS, and OC34S. New frequency measurements are given for nine CO laser transitions between 1686 and 1726 cm−1.

2.5‐THz frequency difference measurements in the visible using metal‐insulator‐metal diodes

Using point‐contact metal‐insulator‐metal diodes, we have demonstrated heterodyne detection of visible laser radiation at frequency differences up to 2.5 THz (generated by a 119‐μm laser). The signal to noise on the observed rf beat falls off at 2.3 dB/octave of laser frequency difference and would seem to indicate that 30‐THz difference beats will be obervable with improved laser stability or signal averaging. While the diode detector ‘‘bandwidth’’ per se has not been evaluated, these measurements demonstrate an increase in the frequency difference which can be measured in the visible by more than an order of magnitude over that previously reported.

Absolute frequency measurements of the 0002-0000, 2001-0000, and 1201-0000 bands of N2O by heterodyne spectroscopy

Abstract The absolute frequencies of 39 lines in the 0002-0000, 2001-0000, and 1201-0000 bands of N2O in the range 4300–4800 cm−1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N2O and two stabilized CO2 lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10−4 cm−1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to −2 MHz/kPa (0 to −0.2 MHz/Torr).