Generation and detection of tunable ultrashort infrared and far-infrared radiation pulses of high intensity

We report on generation and detection of intense pulsed radiation with frequency tunability in the infrared and far-infrared spectral regions. Infrared radiation is generated with a transversally electrically excited high pressure CO₂ laser. A laser pulse of a total duration of about 300 ns consisted, due to self mode locking, of a series of single pulses, some with pulse durations of less than 450 ps and peak powers larger than 20 MW. Using these pulses for optical pumping of a Raman D₂O laser, trains of short far-infrared pulses with durations less than 400 ps were obtained. For detection a new ultrafast superconducting detector was used.     

First realization of new ps-10 mm-CO2-OFID laser systems with far-infrared laser gases as spectral filters

We demonstrate the first operation of a new ps 10 mm CO₂ laser system based on optical free induction decay (OFID) in far-infrared (FIR) laser gases, i.e. CH₃F, D₂O and NH₃. New phenomena are discussed.     

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.     

Optically-pumped pulsed laser action in isotopically-substituted DCN

Pulsed MIR and FIR laser action is reported from D^12,13C^14,15N pumped by a 9 μm region TEA CO₂ laser. Thirty-four wavelengths and assignments are reported, spanning 18.1–477 μm. Output energies from D¹³C¹⁵N at 392 μm pumped by CO₂ 9R(32) are up to a factor of two larger than those from D₂O pumped by 9R(22), one of the strongest known pulsed FIR lasers.     

Optically Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CD3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new FIR, far-infrared, laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2 m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

Optically-Pumped Far-Infrared Laser Lines of Methanol Isotopomers: 12CH3OH, 12CH3OD, and 12CH2DOH

Twenty-seven new far-infrared laser lines from the isotopomers of methanol: ¹²CD₃OH, ¹²CH₃OD, and ¹²CH₂DOH, were obtained by optically-pumping the molecules with an efficient cw CO₂ laser. The CO₂ laser provided pumping from regular, sequence, and hot-band CO₂ laser transitions. The 2-m long far-infrared cavity was a metal-dielectric waveguide closed by two, flat end mirrors. Several short-wavelength (below 100 m) lines were observed. The frequencies of 28 laser lines observed in this cavity (including new lines and already known lines) were measured with a fractional uncertainty limited by the fractional resetability of the far-infrared laser cavity, of 2 parts in 10⁷.     

12CH3OH and 13CH3OH optically pumped by the 10P and 10HP bands of a pulsed CO2 laser: New far-infrared laser emissions and assignments

We have re-investigated the ¹²CH₃OH and the ¹³CH₃OH molecules as optically pumped far-infrared laser sources. We have used our new waveguide pulsed-high-peak-power CO₂ laser for pumping, finding 20 new far-infrared laser lines emitted by ¹²CH₃OH and seven emitted by ¹³CH₃OH. For each line we report wavelength, pump offset from the center of the exciting CO₂ line, relative polarization, optimum operating pressure and intensity. The LaseRitz program was able to assign one of the new laser systems of ¹²CH₃OH, involving two new far-infrared laser lines.PACS 42.55.Lt; 42.62.Fi     

中远红外双波段激光器增益介质匹配

对中远红外双波段激光器中DF和CO2两种增益介质的匹配进行了研究。根据对DF和CO2两种增益介质分布的理论分析,发现DF相比于CO2介质增益峰值位置更靠前,激活区长度更短,据此设计加工了一台双波段激光器,使CO2气体注入孔位置可调,通过D2和CO2注入孔位置的差别来实现两种介质增益峰值位置的匹配。实验证明了这种设计是有效的,并确定了激光器共同光轴的最佳位置位于D2气注入孔下游3 mm,CO2注入孔下游33 mm处,此处双波段激光的输出功率均接近最大值。     

New strong CW FIR laser actions and assignments in COF2

Thirty one new cw far-infrared laser lines have been discovered in COF₂ optically pumped by a CO₂ laser and a N₂O laser, in a metallic waveguide resonator. This number appreciably increases the number of eighteen lines appearing in the literature. Moreover, some of the new lines show that intense far-infrared laser action might be obtained with an optimized cavity, as it was the case for some of the previously reported lines. Twenty-seven, amongst the thirty one new lines, have been fully identified.     

Injection seeding for single-mode operation in an optically pumped high-power D2O laser

Spectrally narrow, pulsed outputs consisting of almost a single mode have been obtained from an optically-pumped high-power (200kW) D₂O laser by adopting the injection seeding method, where single-mode radiation (seed pulse) from a low-power, compact D₂O laser has been injected into the main D₂O laser. Spectrally narrow outputs with high power having spectral widths as narrow as 5 MHz have been obtained, when the seed pulses with frequency tuned to one longitudinal mode of the main D₂O laser have been injected at a time sufficiently before the lasing of the main laser took place. The experimental results have been compared with those of numerical simulation modified to include the injection field with varying injection times.     

Improved deuterium bromide 1-0 band molecular constants from heterodyne frequency measurements

Heterodyne frequency measurements have been made on selected deuterium bromide 1-0 band transitions ranging from P(20) to R(17). Difference frequency beat notes between a tunablediode laser whose frequency was locked to the DBr absorption lines and a CO laser whose frequency was either locked or adjusted to a reference synthesized from CO₂ laser frequency standards were measured. The beat note frequency was then combined with the measured CO laser frequency to give the DBr frequency. For two of the measurements, frequency-doubled CO₂ laser radiation was substituted for the CO laser radiation. The measurements included electric quadrupole split triplets comprising the R(0) and P(1) transitions in the D⁷⁹Br isotope. New DBr constants have been determined, and a table of frequencies is presented for the calibration of spectrometers and tunable lasers in the wavenumber range 1600 to 1990 cm^?1. A table of far-infrared frequencies is also given for DBr covering the range from 50 to 206 cm^?1.     

An injection-locked single-mode tea CO2 laser for SMM laser pumping

A D₂O laser has been developed for collective Thomson scattering measurements of ion temperature in high temperature plasmas. A pulse duration and a spectral width of a high power D₂O laser has been successfully controlled for this purpose, by using a TEA CO₂ laser injection-locked by an etalon-tuned TEA CO₂ laser as a pump source.     

New far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser

In this paper we report on the detection of new far-infrared laser lines from CH₃Cl and CH₃Br optically pumped with a continuously tunable high pressure CO₂ laser. We found 80 new lines for CH₃Cl and 9 new lines for CH₃Br in the frequency region between 16 cm^–1 and 41 cm^–1, all due to stimulated Raman scattering. For the Raman gain regions bandwidths up to about 700 MHz were found. We also observed high intensity short far-infrared laser pulses of durations in the nanosecond regime.Permanent address: Physics Department, State Pedagogical University, SU-119435 Moscow, USSR     

The rotation-vibration constants of the 12CH3F ν3 band

Accurate rotational and vibrational constants for the ground and the ν₃ states of ¹²CH₃F are derived from a simultaneous least-squares fit of all the previous microwave, laser Stark and far-infrared laser data related to the ν₃ ← 0 band. Spectroscopic data, concerning the far-infrared laser emission in ¹²CH₃F, are discussed.     

Predicted new optically pumped FIR molecular lasers

A total of nine cw FIR laser lines are reported from two new FIR laser molecules; CH₂CHF and S¹⁸O₂. These two are from a list of twelve candidate molecules that were predicted using a set of selection criteria. The candidate D₂ ¹⁸O was tested, but did not lase. Combining these results with independent studies on other candidates, brings the number of proven laser molecules to 4 out of 5 that were tested. These results confirm the value of the selection criteria as a guideline for predicting new optically pumped FIR laser molecules.Work supported by the Department of Energy     

Absorption spectrum of deuterated water vapor enriched by 18O between 6000 and 9200 cm−1

The absorption spectrum of water vapor enriched by deuterium and oxygen-18 is analyzed in the 6000–9200 cm^?1 region. The spectrum has been recorded at room temperature with a Bruker IFS 120 h Fourier transform spectrometer. More than 14,000 absorption lines were measured in the recorded spectrum. The vibration–rotation assignments were performed on the basis of previously published experimental energies and of variational calculations. Nine water species (H₂¹⁶O, HD¹⁶O, D₂¹⁶O, H₂¹⁸O, HD¹⁸O, D₂¹⁸O, H₂¹⁷O, HD¹⁷O and D₂¹⁷O) were found to contribute to the observed absorption. More than 3600 lines of 19 vibrational bands of D₂¹⁸O and about 4700 lines of 16 bands of HD¹⁸O with J as high as 19 and K_a as high as 11 were assigned. The main part of the HD¹⁸O and D₂¹⁸O lines and all lines of HD¹⁷O and D₂¹⁷O were observed in the laboratory for the first time. The obtained vibration–rotation energy levels are compared with previous experimental studies and the results of variational calculations.     

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D₂ ¹⁸O vapour, optically pumped with a continuously tunable high pressure CO₂ laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm^–1 to 240 cm^–1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.     

Initiation of nuclear reactions under laser irradiation of Au nanoparticles in the aqueous solution of Uranium salt

Laser exposure of a suspension of either gold or palladium nanoparticles in aqueous solutions of UO₂Cl₂ of natural isotope abundance was experimentally studied. Picosecond Nd:YAG lasers at peak power of 10¹¹–10¹³ W/cm² at the wavelength of 1.06–0.355 μm were used as well as a visible-range Cu vapor laser at a peak power of 10¹⁰ W/cm². The composition of colloidal solutions before and after laser exposure was analyzed using atomic absorption and gamma spectroscopy in the 0.06–1 MeV range of photon energy. Real-time gamma spectroscopy was used to characterize the kinetics of nuclear reactions during laser exposure. It was found that laser exposure initiated nuclear reactions involving both ²³⁸U and ²³⁵U nuclei via different channels in H₂O and D₂O. The influence of saturation of both the liquid and nanoparticles by gaseous H₂ and D₂ on the kinetics of nuclear transformations was found. Possible mechanisms of observed processes are discussed.     

New Far-Infrared Laser Lines and Frequency Measurements of Acetaldehyde and Vinyl Fluoride

Eight far-infrared laser lines have been obtained by optically pumping acetaldehyde (CH₃CHO) and nine by pumping vinyl fluoride (CH₂CHF) with a cw CO₂ laser. The far-infrared laser structure used a metal-dielectric waveguide cavity. This is the first reported observation of four of the laser lines in acetaldehyde. In this work, we measure the frequency, optimum pressure of operation, relative intensity, relative polarization, and pump offset from CO₂ laser-line center.