Doppler-limited Absorption Research Articles

電子ビーム加熱により生成したガドリニウム原子ビームの速度

The velocity of gadolinium atomic beam produced by electron-beam heating was derived from spectrum profiles measured by Doppler-Limited absorption. This method was free from a systematic error of laser beam incident angle because the collimated atomic beam was crossed perpendicularly with laser beams. The atomic velocity was 900 m/s at the deposition rate 30Å/s which was faster than the maximum velocity on the assumption of adiabatic free expansion under estimated evaporation surface temperatures. The excess of kinetic energy indicated a collision induced energy conversion between the atoms excited by electron bombardment.

Velocity Distributions in High Density Gadolinium Atomic Beam Produced with Axial Electron Beam Gun.

The parallel and perpendicular velocity distributions of a gadolinium atomic beam produced with an axial electron beam gun have been measured by a Doppler-shift technique and a Doppler limited absorption spectroscopy, respectively. The atomic density of 1018~1019atoms/m3 at a laser irradiated zone was sufficient for the process, such as an atomic vapor laser isotope separation. The atomic beam velocity of 800 m/s was obtained by a free expansion near an evaporation surface. This velocity, however, was 100 m/s slower than that we had measured with a magnetic transverse electron beam gun in a previous experiment. The reasons for the slower velocity in this experiment than that in the previous one are discussed. In keeping with the deposition rate, the parallel translational temperature rapidly decreased to 200 K, while the perpendicular translational temperature gradually increased and approached to the parallel translational temperature. This result suggested that the collisional region where both translational temperatures are equal extended to the laser irradiated zone in high-rate evaporations.

Electronic absorption spectroscopy of molecular ions in plasmas by dye laser velocity modulation: The A←X system of N+2

A computer controlled velocity modulation dye laser spectrometer is used to measure the A 2Πu←X 2Σ+g (7,3) band of N+2. The Doppler-limited absorption spectra are fit to a model Hamiltonian to obtain precise parameters for the states. The ion rotational temperature was determined to be 461±11, and the translational temperature was estimated to be near 1200 K.

Tunable diode laser Stark modulation spectroscopy for rotational assignment of the HNO 3 7.5 μm band

The technique of Stark modulation spectroscopy for unravelling and assigning rotationally resolved dense molecular spectra has been employed using a tunable diode laser (TDL) source. Doppler-limited absorption and Stark modulation spectra of the HNO 3 7.5 μm band near the 1326 cm −1 band origin are presented, with preliminary values of the excited-state rovibrational constants derived from both TDL and Bomem FTIR spectra.

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).

Generation of continuous-wave 194-nm radiation by sum-frequency mixing in an external ring cavity

Several microwatts of tunable cw radiation near 194 nm in a linewidth of less than 2 MHz have been generated by sum-frequency mixing the radiation from a frequency-doubled argon-ion laser with the radiation from a ring dye laser in a crystal of potassium pentaborate. An external ring cavity resonant with the dye laser gives an enhancement factor of about 14 in the sum-frequency-generated radiation power. The Doppler-limited absorption spectrum of the 6s(2)S((1/2))-6p(2)P((1/2)) first resonance line of natural Hg II has been resolved, and the vacuum wave number for the mass-202 isotope has been measured to be 51485.904(20) cm(-1).

Torsional Splittings and Assignments of the Doppler-Limited Spectrum of Ethane in the C-H Stretching Region.

The Doppler-limited absorption spectrum of the C-H stretching region of ethane has been recorded at T≃ 119 K with a tunable difference-frequency laser spectrometer. The strong torsional hot band structure at room temperature is eliminated at 119 K, and the enhanced resolution from the Doppler width reduction allows us to observe small torsional splittings. The two fundamentals in the region, v 7, a perpendicular band and, v 5, a parallel band have been essentially completely assigned as have a large number of transitions in the parallel component of the v 8 + v 11 combination band. A number of perturbations of both global and local nature have been observed. The complete spectrum and a listing of transition wavenumbers, intensities and assignments are presented here to facilitate identification and quantitative analysis of ethane in a variety of monitoring applications. Precise ground state rotational constants have been determined from combination differences.

High-resolution Fourier spectra of carbon dioxide and three of its isotopic species near 4.3 μm

Low-pressure, Doppler-limited absorption spectra of 16O 12C 16O, 16O 13C 16O, 16O 12C 17O, 16O 12C 18O have been recorded in the 4.3-μm region with a high-information Fourier transform interferometer operating in a vacuum. About 700 absolute wavenumbers achieving at least a tenfold improvement in accuracy over previous measurements are reported with an accuracy of the order of 0.12 × 10 −3 cm −1 (or 3.5 MHz). They may consequently be used as secondary standards. More than 70 molecular constants are reported in this paper.

Gradient-field permanent-magnet spin-flip laser

A CO-laser-pumped InSb CW spin-flip Raman laser has been operated in a permanent magnet (∼1500 G) incorporating a field gradient that permits frequency tuning by moving the magnet relative to the InSb sample. Output lines up to the fifth Stokes and the second anti-Stokes are observed. Real-time Doppler-limited absorption spectroscopy employing a small external modulation coil is demonstrated.

Pressure-tuned GaAs diode-laser absorption spectrocopy of xenon hyperfine structure

The high-resolution and broad tuning-range capabilities of semiconductor lasers under hydrostatic pressure are demonstrated. GaAs diode lasers operating under pulsed chirped mode conditions at 77 K are used to obtain Doppler-limited absorption spectra of several <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6s \rightarrow 6p</tex> transitions in xenon atoms excited in a hollow-cathode discharge. The hyperfine structure so obtained is in agreement with previous spectral studies of xenon isotopes using conventional emission interferometric and RF beam techniques.