Laser frequency measurements and spectroscopic assignments of optically pumped 13CH3OH

A three-laser heterodyne system was used to measure the frequencies of twelve optically pumped laser emissions from ¹³CH₃OH in the far-infrared (FIR) region. These emissions, ranging from 54 to 142 μm, are reported with fractional uncertainties up to ±2×10^-7 along with their polarization relative to the CO₂ pump. Using the 9P32 and 10R14 CO₂ lines, complete spectroscopic assignments for two laser systems were confirmed. Received: 31 May 2001 / Published online: 19 September 2001     

Discovery and measurement of optically pumped far-infrared laser emissions in 13CD3OH

We report the discovery of four laser emissions from the partially deuterated C-13 methanol isotope ¹³CD₃OH when optically pumped with a cw carbon dioxide (CO₂) laser. The wavelengths of these lines, ranging from 45.3 to 108.9 m, are reported along with their polarizations relative to the CO₂ pump laser, operating pressure, and relative intensity. A three-laser heterodyne system was then used to measure the frequencies of eight optically pumped laser emissions from this methanol isotope. These emissions range from 53.4 to 126.1 m and are reported with fractional uncertainties up to ±2×10^-7. PACS 07.57.Hm; 42.55.Lt     

An acoustooptic method of measuring the noise equivalent power of optical heterodyne systems

The noise equivalent power of optical heterodyne detection at 10.6 m has been measured with a method based on Raman-Nath diffraction of a CO₂ laser beam. One of the frequency shifted first order diffracted beams is used as the signal radiation. The local oscillator radiation is obtained by splitting off a part of the laser beam incident upon the device used for the acoustooptic diffraction. The signal power can be varied over a large dynamic range by changing the acoustic input power. A study of the probable errors shows that the total error in the NEP measurement is less than 30%.     

Discovery and frequency measurement of short-wavelength far-infrared laser emissions from optically pumped <Superscript>13</Superscript>CD<Subscript>3</Subscript>OH and CHD<Subscript>2</Subscript>OH

A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions from the partially deuterated methanol isotopologues ¹³CD₃OH and CHD₂OH. Two laser emissions, a 53.773 μm line from ¹³CD₃OH and a 74.939 μm line from CHD₂OH, have also been discovered and frequency measured. The CO₂ pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH₃OH, ¹³CD₃OH and CHD₂OH. PACS 07.57.Hm; 42.55.Lt; 42.62.Eh     

The CO fundamental-band laser as secondary frequency standard at 5 µm

We present a very high-resolution heterodyne spectrometer based on a CO laser which operates down to fundamental-band transitions of the molecule. This allows us to detect saturated absorption signals on these transitions at very low pressure (0.4 Pa) and laser intensity (< 1 mW/cm²), yielding a linewidth of about 250 kHz. With the CO fundamental-band laser stabilized to these saturation signals we have measured the transition frequencies of the fundamental bands of three isotopic species to an accuracy of typically 20 kHz (v/v 3 × 10^–10), referenced to the CO₂ frequency standard. Together with additional frequency measurements of the first hot bands, these provide the first heterodyne frequency data of sub-Doppler accuracy for transitions in low lying bands of CO. They now represent the most accurate secondary frequency standard in the spectral region around 5 µm (60 THz).     

Electric quadrupole interactions of europium in alkali europium tungstates by Mössbauer and laser spectroscopies

¹⁵¹Eu Mössbauer spectroscopy and optical-r.f. double resonance spectroscopy measurements of the quadrupole interaction parameters in KEu(WO₄)₂ give good agreement and are of comparable accuracy, while laser heterodyne spectroscopy measurements provided improved accuracy by an order of magnitude. However in the crystallographically disordered compound NaEu(WO₄)₂, Mössbauer spectroscopy was more suited to producing fittable spectra. The difference in the hyperfine field of the two compounds in a 9 T applied field is attributed to a transferred hyperfine interaction.     

Wide band (2.5 GHz) infrared heterodyne spectrometer

Conclusion A double beam heterodyne spectrometer with 2.5 GHz bandwidth was built in Reims. The receiver's bandwidth was measured by heterodyning radiation from a CO₂ laser with the radiation from a tunable diode laser. The spectrometer was used for laboratory studies. Ammonia absorption spectra were recorded. Line positions in agreement with other works were measured.This apparatus will soon be used for atmospheric ozone studies in association with an isotopic¹²C¹⁸O₂ laser to avoid atmospheric CO₂ absorption.     

Discovery and frequency measurement of far-infrared laser emissions generated by optically pumped CH2DOH

A recently improved three-laser heterodyne system was used to frequency measure ten previously observed optically pumped far-infrared (FIR) laser emissions from the partially deuterated methanol isotopologue CH₂DOH. Also, a 64.0 μm FIR emission generated by the 9P32 line of the carbon dioxide (CO₂) laser was discovered and frequency measured. These newly measured frequencies have fractional uncertainties on the order of ±2×10^-7 and correspond to laser wavelengths ranging from 42.6 to 152.7 μm. The offset frequency for the CO₂ pump laser was measured for twenty-two CH₂DOH FIR laser emissions. PACS 07.57.Hm; 42.55Lt; 42.62.Eh     

Diode laser heterodyne measurements on 14NH3

The frequencies of 32 absorption lines of ¹⁴NH₃ were measured to within 2 × 10^?4 cm^?1 in the 9- and 10-μm regions by use of a diode laser heterodyne spectrometer.     

Measurement of far-infrared laser frequencies generated by optically pumped N 2 H4 and N2D4

A three-laser heterodyne system has been used to measure the frequencies of four previously observed far-infrared laser emissions generated by optically pumping either hydrazine (N₂H₄) or its fully deuterated isotope (N₂D₄) with a continuous-wave carbon dioxide laser. These newly measured frequencies have fractional uncertainties of ± 2 × 10⁻⁷ and correspond to laser wavelengths ranging from 63.9 to 158.4 μm. This work represents the first measurement of a N₂D₄ laser frequency.     

Frequency Measurements of Optically Pumped Laser Emissions from the CHD2OH Methanol Isotope

A threelaser heterodyne system was used to measure the frequencies of eleven optically pumped laser emissions from CHD₂OH in the farinfrared (FIR) region. These frequencies, reported with fractional uncertainties of the order ± 2 × 10^–7, are for emissions ranging from 102.9 to 212.4 m. To our knowledge, these measurements are the first reported FIR laser frequencies for the CHD₂OH methanol isotope when used as an optically pumped laser medium.     

双波长绝对距离外差干涉仪的研究

提出了一种采用双纵模稳频激光器的新型绝对距离测量外差干涉仪。该干涉仪探测两个波长各自的外差信号, 通过测量两信号的相位差, 直接测量出合成波的小数级次。指出了两波长间的相互耦合对测量精度的影响, 提出了补偿方法, 在２５ ｍ 的测量范围取得了 １４０ μｍ 的测量精度。     

Tunable electrooptically Q-switched RF excited CO2 waveguide laser with two channels

A tunable electrooptically Q-switched RF excited waveguide CO₂ laser with two channels is presented. Q-switched pulses have been obtained from one of the channels. The peak power is 300 W and the pulse width is 140 ns. CW laser output has been obtained from the other channel, which can been tuned by a PZT. The short-term heterodyne stability can be up to 10⁻⁹.     

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

Frequency measurements are given for the 00⁰1-00⁰0 and 01¹1-01¹0 bands of N₂O 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 N₂O absorption line and harmonic combinations of frequencies of radiation from two CO₂ 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 N₂O 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.     

A cw CO2 laser rangefinder using heterodyne detection and on-off amplitude modulation

A CO₂ laser rangefinder has been built that uses an acousto-optic modulator to obtain an amplitude modulated optical beam from a cw laser. An on-off deflected beam was obtained by driving the modulator with a carrier modulated by a periodic binary code. The received infra-red radiation was heterodyne detected. After envelope detection of the heterodyne signal, the signal-to-noise ratio was improved by applying a digital integrator. Ranging was carried out by calculating the delay of the received code by means of a cross-correlation technique. For this purpose a minicomputer was implemented in the system. Using 1 W average beam power and measuring times less than 1 s, ranges of several kilometers have been determined from stationary targets.     

Hyperfine structure and absolute frequency measurements of <Superscript>127</Superscript><Emphasis Type="Italic">I</Emphasis><Subscript>2</Subscript> transitions with monolithic Nd:YAG 561-nm lasers

The precision hyperfine structures of the ¹²⁷ I ₂ transitions at 561.4 nm are measured by the heterodyne beat between two home-made ¹²⁷ I ₂-stabilized Nd:YAG lasers. The theoretical distributions of the observed transitions’ hyperfine sublevels are used to identify the two transitions. High-accuracy hyperfine constants are obtained by fitting the measured hyperfine splittings to the four-term Hamiltonian, which includes the electric quadruple, spin-rotation, tensor spin–spin and scalar spin–spin interactions. The absolute frequencies of the observed four transitions are measured by an optical frequency comb based on a mode-locked erbium-fiber laser.     

CO-laser side-band spectrometer: Sub-Doppler heterodyne frequency measurements around 5 µm

We report the realization of a tunable sub-Doppler heterodyne spectrometer with high absolute accuracy, employing side-band generation with a CO laser. The fixed-frequency CO-gas laser, working from 4.7 to 8.4µm, is made partially tunable by the use of microwave side-band generation in a CdTe Electro-Optical Modulator (EOM). This leads to tunable radiation of high spectral purity. We describe the design of the microwave EOM, adapted to the CO laser, its performance and its first application to highly accurate frequency measurements. The side-band radiation is used for sub-Doppler stabilization of the CO laser, while the carrier frequency is mixed with the frequencies of two CO₂ reference lasers. As a first result, we present measurements of OCS transitions in the 4.9µm (61 THz) region, reaching an absolute accuracy of 30 kHz (/ = 5×1O^–10). Further application of our spectrometer to calibration gases will establish a variety of InfraRed (IR) calibration standards with a new quality of accuracy. On visit from: Fachbereich Physik, Humboldt-Universität zu Berlin     

Frequency measurement of optically pumped FIR laser emissions from the CH3OD methanol isotope

A three-laser heterodyne system has been used to measure the frequencies of seven previously observed optically pumped FIR laser emissions generated by the CH₃OD methanol isotope. The frequencies, measured for the first time, are reported with fractional uncertainties up to ±2×10^-7 for laser emissions ranging in wavelength from 80.1 to 183.3 m. A previously measured FIR laser emission from CH₃OD, observed at 57.2 m, was also re-measured in this work. PACS 07.57.Hm; 42.55Lt; 42.62.Eh     

A 729 nm laser with ultra-narrow linewidth for probing 4S1/2-3D5/2 clock transition of Ca

A Coherent Inc. Ti:sapphire laser MBR-110 is locked to a temperature-controlled high finesse Fabry-Perot cavity supported on an isolated platform. The linewidth is measured by locking the laser to another similar super-cavity at the same time and the heterodyne beatnote between two laser beams that locked to different cavities determines the linewidth. The result shows that the laser's linewidth is suppressed to be 41 Hz. The long-term drift is measured with a femtosecond comb and determined to be ~ 0.1 Hz/s. This laser is used to probe the 4S_1/2-3D_5/2 clock transition of a single ⁴⁰Ca⁺ ion. The Zeeman components of the clock transition with a linewidth of 160 Hz have been observed.     

Dynamics of high-temperature plasma formation during laser irradiation of three-dimensionally structured,low-density matter

Results are presented from an experimental investigation of the properties of the plasma produced by the action of a radiation pulse at the second harmonic of a Nd laser, with average intensity ~5·10¹⁴ W/cm² in the focal spot, on flat targets consisting of porous polypropylene (CH)_x with an average density of 0.02 g/cm³ (close to the critical plasma density) and with ~50 μm pores. The properties of the laser plasma obtained with porous and continuous targets are substantially different. The main differences are volume absorption of the laser radiation in the porous material and much larger spatial scales of energy transfer. The experimentally measured longitudinal ablation velocity in the porous material was equal to (1.5–3)·10⁷ cm/s, which corresponds to a mass velocity of (3–6)·10⁵ g/cm²· s, and the transverse (with respect to the direction of the laser beam) propagation velocity of the thermal wave was equal to ~(1–2) ·10⁷ cm/s. The spatial dimensions of the plasma plume were ~20–30μm. The plasma was localized in a 200–400μm region inside the target. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 462–467 (10 October 1996)