J.S. Wells

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.

Continuous-wave frequency tripling and quadrupling by simultaneous three-wave mixings in periodically poled crystals: application to a two-step 1.19–10.71-µm frequency bridge

We observed cw third-harmonic generation in a periodically poled LiNbO(3) crystal by cascading optimally phase-matched second-harmonic and sum-frequency generation. Other processes, such as fourth-harmonic generation, are allowed by the flexibility of quasi-phase matching. We demonstrate a divide-by-nine (1.19- 10.71-microm) frequency chain that uses only two lasers.

High resolution wavenumber standards for the infrared (Technical Report)

The calibration of high resolution infrared spectra is generally more precise than accurate. This is the case even when they are recorded with Fourier transform interferometers. The present document aims at improving the accuracy of wavenumber measurements in the infrared by recommending a selection of spectral lines as wavenumber standards for absolute calibration in the range from about 4 to about 7000 cm(-1). The uncertainties of these wavenumber standards range from 4+/-1x10(-3) to +/-1x10(-6) cm(-1). Sources of frequency standards, on which the wavenumber determinations are based, are also given.

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).

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.

Heterodyne frequency measurements on N2O between 1257 and 1340 cm−1

Abstract Frequency measurements are given for the 00 0 1-00 0 0 and 01 1 1-01 1 0 bands of N 2 O from 1257 to 1340 cm −1 . The measurements utilize heterodyne techniques by measuring small frequency differences between a tunable diode laser locked to the center of an N 2 O absorption line and harmonic combinations of frequencies of radiation from two CO 2 Lamb-dip-stabilized lasers. The measurements are facilitated by the use of the CO laser as a transfer laser whose frequency is also measured. These measurements have been combined with other data to provide new band constants and frequency calibration tables for several band systems of N 2 O in the following regions; 1215 to 1340, 1816 to 1930, and 2135 to 2268 cm −1 . A correction factor is also provided for existing calibration tables near 590 cm −1 .

Calibration tables covering the 1460- to 1550-cm−1 region from heterodyne frequency measurements on the ν3 bands of 12CS2 and 13CS2

Abstract Heterodyne frequency measurements have been made on the ν 3 band of both 12 CS 2 and 13 CS 2 near 1500 cm −1 . The data were fitted and new molecular constants determined. Values for the constants and newly calculated frequency calibration tables are presented. The calibration tables cover the range from 1460 to 1550 cm −1 .

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).

Heterodyne frequency measurements on N 2 O at 5.3 and 9.0 μm

Heterodyne frequency measurements on the 0111–0000 band of N2O have been made with the use of a tunable-diode laser, a CO laser transfer oscillator, and a CO2 laser frequency synthesizer. A beat frequency was measured between a CO laser and a tunable-diode laser whose frequency was locked to the peak of N2O absorption features. The frequency of the CO laser was simultaneously determined by measuring the beat frequency with respect to a reference synthesized from two CO2 lasers. New rovibrational constants are given for the 0111 state of N2O, which are in excellent agreement with previous results, although the band center is 4 MHz higher than in the previous measurements. A table of the line frequencies and their absolute uncertainties is given for the N2O absorption lines in the wave-number region from 1830 to 1920 cm−1. Some additional frequency measurements near the lower-frequency end of the 0200–0000 band have also been made with respect to a 12C18O2 laser.