Ultrashort far-infrared superradiant emissions optically pumped by truncated hybrid 10 μm CO2 laster pulses

We investigate the generation of superradiant far-infrared 496 m CH₃F pulses and produce for the first time smooth and reproducible 373 m CH₃CN superradiant pulses by pumping with pulses from a hybrid 10 m CO₂ laser truncated within 10 ps by a plasma shutter of new design. Superradiance is confirmed by measurement of the pressure dependence of the intensity, the width and the delay versus the pump pulse. We observe pulse durations considerably under the limit of the inverse linewidth of the transition. Thus, we demonstrate for the first time that rapid truncation of the pump pulse is essential for reducing pulse duration of superradiant far-infrared emissions.     

Optically pumped14NH3 laser and its stark tuning at 10.78 μm

Infrared (ir) emissions from a TEA-CO₂-laser-pumped NH₃ laser are reported. Superfluorescent emissions and selective single-line oscillations have been obtained in the range from 11 to 13 m. The results make possible the design of a NH₃ Stark cell allowing a 1 GHz shift of the 10.78 m NH₃ emission line.     

The refractivity of CO2 gas in the region of 10 μm

The refractivity of the CO₂ gas is measured with an experimental error of 2% in the 10-m region, using 10.4-m band CO₂ laser line. The frequency of the CO₂ laser is swept through the Doppler profile of the laser line. The experiment is achieved using a 0.63-m He–Ne/10.6-m CO₂-laser interferometer with a 2-m long vacuum cell. From the result, it is found that the Koch's formula also holds for the wavelengths in the 10-m region within an accuracy of 2%.     

High-resolution IR spectra of methyleneimine (CH2NH) in the 10 μm region,the ν8 band

The IR spectrum of methyleneimine (CH₂NH) has been observed in the gas phase with a resolution of 0.0048 cm⁻¹ using the KPNO Solar Fourier transform spectrometer. The short-lived CH₂NH was produced in a flow system by the pyrolysis of CH₃NH₂ at ca. 1000°C. The origin of the ν₈ band was determined to be 1126.95 (6) cm⁻¹. Preliminary calculations of the strong Coriolis interactions between the ν₇, ν₈ and ν₉ bands have been made.     

Parameter study and computer simulation of an optically pumped mirrorless laser at 496 μm in methyl Fluoride and 385 μm in heavy water

The effects produced in an optically pumped mirrorless far-infrared laser assembly by varying pumping power, gas pressure, and tube length have been investigated. It is found that absorption of pumping radiation depends only on the number of absorbing molecules; far-infrared output peaks when gas pressure is such that approximately two-thirds of pump radiation is absorbed, and peak far-infrared output increases with tube length, even though the total number of absorbing molecules remains constant.A computer simulation for the mirrorless laser based on Javan's three-level rate equation model but retaining one-dimensional spatial dependence is presented and compared with experimental results.     

Frequency measurements in the 10 μm spectrum of 11BCl3

This paper presents a study of the spectroscopy of ¹¹BCl₃ using the Doppler-free saturated absorption technique. Many lines in the degenerate ν₃ fundamental of this molecule have been recorded using the 10P branch of a carbon dioxide laser. The absolute frequencies of the linecentres of these absorptions have been measured to an accuracy of better than 10 kHz, using frequencies calibrated against transitions in SF₆ and OsO₄. Hyperfine structure due to the Cl nuclei was easily resolved, and more detailed structure, which may be attributed to the ¹¹B quadrupole interaction, was also seen. The splittings between individual quadrupole components were measured to an accuracy of better than 2 kHz where SF₆ references were used, and to about 8 kHz in the case of OsO₄. Peak-to-peak linewidths as low as 22 kHz have been recorded, representing the highest resolution data yet obtained for this molecule.     

Superfluorescent fiber source at 3.9 μm in the attenuation minimum of the atmospheric window 3–5 μm

Superfluorescence has been demonstrated for the first time at 3.9m in holmium-doped fluoride glass optical fiber. Fluorescence measurements were possible at room temperature while pumping around 650 nm. Cooled to 173 K superfluorescence was obtained.     

NaK 22Σ+ → 11Σ+ band optically pumped laser near 1.02 μm

Optically pumped laser emission has been observed on the NaK 2(A)¹⁺ 1(X)¹⁺ electronic state transition. The emission occurs between 1.015 and 1.035 m when a sodium-potassium heat-pipe oven is pumped with 695–745 nm pulsed dye laser radiation. The laser emission occurs on many ro-vibrational transitions without the use of cavity mirrors. However, the addition of a simple cavity increases both the number of observed lasing transitions and the amplitude of the emission on each line. We report our results for the dependence of the emission intensity on pump laser power, oven temperature, and buffer gas pressure.     

Pulsed quantum-cascade-laser spectroscopy with intermediate-size pulses: application to NH3 in the 10 μm region

Pulsed quantum-cascade-laser spectrometers are usually used to detect atmospheric gases with either the interpulse technique (short pulses, typically 5–20 ns) or the intrapulse technique (long pulses, typically 500–800 ns). Each of these techniques has its drawbacks. Particularly the gas absorption spectra are generally distorted. We have previously developed another technique called intermediate-size pulses (typically 50–100 ns) technique for gas detection using pulsed QCL spectrometers. In this paper, infrared spectra of ammonia recorded with this technique in the 10 μm region are presented. For the NH₃ spectra recorded at low pressure (i.e. in the mbar range), the spectra show typical oscillations after the absorption. The Beer–Lambert law cannot explain these oscillations, termed the rapid-passage effect. Comparisons between experimental and calculated spectra will be realized. This phenomenon is not satisfactory from a spectroscopic point of view and spectra must be recorded at higher pressures. For the NH₃ spectra recorded at higher pressure (i.e. in the 50 mbar range), the oscillations disappear and the Beer–Lambert law could be reused. This paper will demonstrate that the intermediate-size technique gives reliable measurements for NH₃ detection. Moreover the typical apparatus function (0.003 cm⁻¹ HWHM) is far lower from the typical apparatus function of the interpulse QCL spectrometers (0.015 cm⁻¹ HWHM).     

Visualization of weak IR signals from anti-stokes luminophores in the 1.4–1.7 μm region

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 1, pp. 104–110, July, 1991.     

10-mJ optically synchronized CEP-stable chirped parametric amplifier at 1.5 μm

We demonstrate the generation of 10-mJ 1.5-μm few-cycle pulses from a 4-stage OPCPA system. The system is based on a fusion of femtosecond DPSS Yb technology and a picosecond Nd:YAG pump laser. In a first preliminary filamentation experiment in argon at 5 atm, we observe significant spectral broadening of the recompressed multi-mJ 1.5-μm pulses. The filamentation output spectrum supports the generation of 8 fs pulses equivalent to sub-to-cycle pulses at 1.5 μm. We foresee that our terawatt-peak-power sub-to-cycle pulse source will open the door to exciting new experiments in attosecond high-field science in the near future.

     

Saturable absorbers for passive Q-switching of erbium lasers emitting in the region of 3 μm

The phototropic properties of Fe:ZnSe, Co:ZnSe, and Co:ZnS single crystals have been investigated. It is shown that these crystals can be used to advantage as the saturable absorbers in solid-state erbium lasers emitting in the region of the 3-μm range. The absorption cross sections of the ground states of the Co²⁺ ion in the ZnSe (σ_GSA = 11·10⁻²⁰ cm²) and ZnS (σ_GSA = 5.6·10⁻²⁰ cm²) crystals and of the Fe²⁺ ion in the ZnSe (σ_GSA = 50·10⁻²⁰ cm²) crystal at λ = 2.79 μm were determined experimentally. It has been established that the above-indicated crystals in the excited state absorb light weakly. The use of these crystals as passive Q switches made it possible to realize, for the first time, the regime of Q-switching of a Cr,Er:YSGG laser emitting at a wavelength of 2.79 μm. Single pulses with an energy of 60 mJ and a duration of 170 nsec were obtained in the regime of passive Q-switching. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 747–751, November–December, 2005.     

Tunable large angular aperture TeO2 acousto-optic filters for use in the 1.0–1.6 μm region

The design of tunable large angular aperture TeO₂ noncollinear acousto-optic filters for use in the 1.0–1.6m region is discussed. It is shown that it is possible to maximize the angular aperture of such a filter by the correct choice of the direction for the acoustic wave vector and that this required direction is independent of the operating wavelength in the range 1.0–1.6m. The theoretical model adopted is verified by comparison with experimentally measured filter characteristics and the design of filters with narrow bandwidths and low power requirements is discussed.     

Injection lasers in the 1.3–1.8 μm wavelength range

Conclusion There are developed techniques for the preparation of diode lasers in the 1.3 to 1.8 m range on the basis of quaternary epitaxial heterostructure. Devices for a particular wavelength of 1.3 m are now commercially available. The state of art in the laser studies with connection to lower room-temperature threshold and to higher operation temperature is illustrated in fig. 9. We feel that the laser system of InGaAsP, which is known since 1974 [1, 2], may be elaborated further for higher laser characteristics in spite of the fact that present state is quite acceptable for different applications. There are many fibre-optics projects based on the conception of laser optical communication with the use of diodes in the range of 1.3–1.8 m.Invited talk at the International Conference on Radiative Recombination and Related Phenomena in III–V Compound Semiconductors, Prague, 4–7 October, 1983.The author is indebted to Dr. L. M. Dolginov, B. N. Sverdlov, A. E. Drakin, P. A. Louk, E. G. Shevchenko for the help in this work.     

Efficient all-solid-state mid-infrared optical parametric oscillator based on resonantly pumped 1.645 μm Er:YAG laser

We first report an all-solid-state tunable mid-infrared singly resonant optical parametric oscillator based on a 1532 nm laser diode resonantly pumped, Q-switched 1.645 μm Er:YAG laser. An MgO-doped periodically poled lithium niobate was used as the nonlinear material. At the pulse repetition frequency of 2 KHz, a maximum overall average output power of 0.95 W with pump power of 2.8 W was achieved, corresponding to a conversion efficiency of 34% and a slope efficiency of 38%. The temperature tuning was performed giving signal and idler ranges of 2.67 to 2.71 μm and 4.18 to 4.31 μm, respectively.     

Coherent beam combination of narrow-linewidth 1.5 μm fiber amplifiers in a long-pulse regime

We report what we believe to be the first experimental demonstration of coherent beam combining of two fiber amplifiers in a 100 ns pulse regime using a signal leak between the pulses. Pulses of ～100 W stimulated-Brillouin-scattering limited peak power are combined with 95% efficiency, a residual phase error of λ/27, and no significant beam quality degradation.     

MIDI,the 10 μm interferometer of the VLT

We report in this paper on the current status of the mid-infrared beam combiner of the VLTI: MIDI. We explain the interest of VLTI for this range of wavelentghs and give an overview of the main characteristics of MIDI and present its scientific targets.     

High-resolution cavity leak-out absorption spectroscopy in the 10-μm region

2 laser. After excitation, the laser power is turned off for a short time and the subsequent decay of the radiation stored in the cavity is observed via detection of the light leaking out through one of the cavity mirrors. Measurement of the decay time allows one to determine the photon losses und thus to detect weakly absorbing species inside the cavity. Since the cavity is frequency-locked to the laser the decay time can be probed with a high repetition rate, basically limited by the sampling rate of the analog-to-digital converter. This approach is closely related to cavity ring-down spectroscopy with pulsed lasers, but exhibits several advantages concerning spectral resolution and detection sensitivity. As a practical example we demonstrate monitoring of trace amounts of ethylene. Using R=99.5% mirrors we achieve a detection limit of 1 ppb ethylene (integration time: 100 s) corresponding to absorption losses of 3×10^-8 /cm. Further improvement is feasible when mirrors with higher reflectivity become available. Received: 2 July 1998