Hiroyuki Sasada

Calibration lines of HCN in the 1.5-μm region

Near-IR distributed feedback semiconductor laser spectroscopy of HCN in natural abundance and in an H(13)CN-enriched sample has been performed from 6380 to 6410 cm(-1). Absolute accuracy of wavenumber measurement was 0.0005 cm(-1) using the 3-0 band of CO as a reference. New sets of molecular constants for the (2 0(0) 0)-(0 0(0) 0) and (2 1(1) 0)-(0 1(1) 0) bands of H(12)C(14)N and H(13)C(14)N have been determined by combining the present results together with the existing data. Two tables of the calculated wavenumbers are given for calibration standards in the 1.5-microm region.

High-resolution infrared and microwave spectroscopy of the ν4 and 2ν2 bands of 14NH3 and 15NH3

Abstract More than two thousand Stark resonances of the ν 4 and 2 ν 2 band transitions of 14 NH 3 and 15 NH 3 were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on 15 NH 3 is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v 4 = 1 excited vibrational state of 14 NH 3 and 15 NH 3 . Accuracies of all available spectroscopic data on the v 4 = 1 and the v 2 = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v 4 = 1 a (antisymmetric level) and v 2 = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v 4 = 1 a and the v 2 = 1 s states and between the v 2 = 2 s and the v 2 = v 4 = 1 a states (i.e., ( v 1 , v 2 , v ′ 3 , v ′ 4 ) = (0 1 0 0 1 1 )) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10 −6 . The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm −1 .

Highly Sensitive Cavity-Enhanced Sub-Doppler Spectroscopy of a Molecular Overtone Band with a 1.66 µm Tunable Diode Laser

Sensitive sub-Doppler resolution molecular spectroscopy developed by Hall and co-workers [J. Opt. Soc. Am. B 15 (1998) 6] has been applied to the 1.66 µm region using a widely tunable external-cavity diode laser. We have recorded saturated absorption spectra of the 2ν3 vibrational overtone band of methane with a sensitivity of 9.5×10-11 cm-1 at a time constant of 1.25 s and a spectral linewidth of 320 kHz (full width at half maximun; FWHM) over the tunable range of 1.63 to 1.68 µm.

Microwave and Fourier-transform infrared spectroscopy of the v4 = 1 and v2 = 2 s states of NH3

Seventy-nine microwave transitions of the v4 = 1 and v2 = 2 s states of 14NH3, including two forbidden rotational transitions with the selection rules Δk = ±1, Δl = ⊣2, have been measured up to 400 GHz. The ν4 and 2ν2 s band spectra of the molecule have also been recorded by a Fourier-transform infrared spectrometer with a resolution of 0.005 cm−1 and an accuracy of 0.0002 cm−1. More than 700 infrared transitions have been assigned up to the J = 14 rotational levels. The obtained microwave and infrared data were fitted to a 91-parameter Hamiltonian in which several Δ(k − l) = ±3 interaction terms were explicitly considered together with existing microwave results. The determined molecular constants for the v4 = 1 and v2 = 2s states reproduce the observed data with a root mean square deviation of 0.00038 cm−1.

Ultra-broadband dual-comb spectroscopy across 1.0–1.9 µm

We have carried out dual-comb spectroscopy and observed in a simultaneous acquisition a 140-THz-wide spectrum from 1.0 to 1.9 µm using two fiber-based frequency combs phase-locked to each other. This ultrabroad-wavelength bandwidth is realized by setting the difference between the repetition rates of the two combs to 7.6 Hz using the sub-Hz-linewidth fiber combs. The recorded spectrum contains five vibration-rotation bands of C2H2, CH4, and H2O at different wavelengths across the whole spectrum. The determined transition frequencies of C2H2 agree with those from the previous sub-Doppler resolution measurement of individual lines using CW lasers within 2 MHz.

1.5 μm DFB semiconductor laser spectroscopy of HCN

Near‐infrared DFB (distributed feedback) semiconductor lasers have been extensively applied to molecular spectroscopy for the first time. The overtone band of three isotopic species of HCN has been recorded from 6420 to 6590 cm−1 without any frequency gaps, and three hot bands of H12C14N have also been observed. The molecular constants of the observed bands and the dipole moment for the (0 00 2) state of H12C14N are obtained.

1.5-μm DFB semiconductor laser spectroscopy of deuterated water

Abstract Absorption spectra of the ν 1 + ν 3 and 2 ν 2 + ν 3 bands of HDO and the ν 1 + ν 2 + ν 3 and 2 ν 1 + ν 2 bands of D 2 O have been recorded from 6380 to 6600 cm −1 by using single-mode distributed feedback semiconductor lasers (DFB lasers) with an experimental accuracy of about 0.004 cm −1 . An analysis of the HDO spectrum was successfully carried out by taking account of both Coriolis and Fermi interactions between the (101) and (021) states. In the D 2 O molecule, the Coriolis interaction between the (111) and (210) states was clearly observed and a preliminary set of the rotational and coupling constants was determined.

Optical frequency measurement of the H 12 C 14 N Lamb-dip-stabilized 1.5-μm diode laser

We have measured the frequency of the P(27) line of H(12)C(14)N at 1556 nm, using the 778-nm two-photon transition of Rb as a frequency reference. The measured frequency was 192, 622, 446.9 +/- 0.1 MHz. We believe that this experiment is the first absolute frequency measurement of a laser stabilized to a saturation dip at 1.5 microm and also the most accurate measurement of a 1.5-microm optical frequency.

Wavenumber measurements of sub-Doppler spectral lines of Rb at 1.3 mu m and 1.5 mu m

1.3- mu m and 1.5- mu m distributed-feedback semiconductor lasers have been frequency stabilized to sub-Doppler resonances of the 5P/sub 1/2/ to 6S/sub 1/2/ and the 5P/sub 3/2/ to 4D/sub 3/2,5/2/ transitions of /sup 85,87/Rb atoms, respectively. Using these stabilized lasers, the absolute wavenumbers of the transitions have been measured interferometrically with an accuracy of 2*10/sup -7/.<<ETX>>

Absolute frequency list of the ν 3 -band transitions of methane at a relative uncertainty level of 10 −11

We determine the absolute frequencies of 56 rotation-vibration transitions of the ν(3) band of CH(4) from 88.2 to 90.5 THz with a typical uncertainty of 2 kHz corresponding to a relative uncertainty of 2.2 × 10(-11) over an average time of a few hundred seconds. Saturated absorption lines are observed using a difference-frequency-generation source and a cavity-enhanced absorption cell, and the transition frequencies are measured with a fiber-laser-based optical frequency comb referenced to a rubidium atomic clock linked to the international atomic time. The determined value of the P(7) F(2)((2)) line is consistent with the International Committee for Weights and Measures recommendation within the uncertainty.