On longitudinal mode spacing of laser cavities with pairs of gratings

It has recently been suggested that a laser cavity formed by a pair of gratings would show anomalously large longitudinal mode spacing which should favor single-longitudinal-mode emission. An experimental verification of that prediction with a TEA-CO₂ laser is presented. The repeatedly negative results obtained under various conditions are given a tentative explanation, based on the well-known analysis of a closely related problem: the grating-pair pulse compression scheme.     

Assignments of fir laser emissions from CH3OH optically pumped by an intra-cavity etalon tuned TEA-CO2 laser

The author reports that TEA-CO₂ with an intra-cavity etalon is a useful pumping source which can deliver widely tunable beam (tunable range 1 GHz) with accurate oscillation frequencies and with high power compared to a tunable wave guide laser.The source is applied to the excitations of CH₃OH and the FIR emissions from it are well assigned for there absorption transitions and FIR emissions. This proves that the source display not only usefulness for development of new FIR emissions but also for molecular spectroscopy.     

Spikes in raman spectrum of miniature optically pumped NH3 fir laser

In this paper, the semiclassical density matrix equation was solved to calculate the spectral characteristics of V₂:a--sR(0,0) transition in a miniature optically pumped NH₃ far infrared laser (mini-NH₃-OPFIRL), which was pumped by CO₂-10R(6) line. The results of theoretical calculation showed that the spikes in Raman spectrum of V₂:a--sR(0,0) would appear when the operating NH₃ gas pressure was higher than a certain critical value or pumping power density was lower than a certain critical value, which was caused by Raman processes interaction of AC-Stark splitting. In our experiment, 298 µm FIR spetral line of a--sR(0,0) pumped by a TEA-CO₂ laser with 10R(6) line was observed but the spikes could not be observed owing to the limitation of the resolution of the F-P interferometer.Supported by the National Natural Sciences Foundation of P.R.China.     

A study of the compounds which are induced on the metallic target surface under the action of a pulsed laser plasmatron

The compounds induced on the surface of titanium and copper targets by a breakdown plasma produced by focused TEA-CO₂ high-repetition frequency laser pulses was studied by transmission electron microscopy and selected area diffraction in correlation with absorptivity data determined before and after laser irradiation. The possibility of using TEA-CO₂ lasers to produce complex thermal treatments was demonstrated for metallic surfaces by the modification of the physico-chemical properties at the sites of plasma action on these surfaces.     

基于光放大的长脉冲抽运太赫兹激光

为了获得较窄增益带宽、较大光强的太赫兹辐射,尝试了利用TEA CO₂激光器对6 W可调谐连续波CO₂种子激光实行双程光放大实验,以期望获得长脉冲、高峰值功率的抽运光.通过实验,获得了大约30倍的放大系数,放大光输出功率随种子光注入功率的增加而增加,其中10 P （20）支线表现更加突出,并且被放大的激光支线半峰全宽在14 μs左右.基于这种长脉冲抽运源,建立了一种产生脉冲太赫兹的动力学模型,给出了产生太赫兹辐射的饱和抽运光强表达式,确定了抽运光的光强范围.另外, 关键词： 激光物理 长脉冲 动力学模型 太赫兹激光     

Fracture mechanisms of Hg0.8Cd0.2Te induced by pulsed TEA-CO2 laser

The fracture mechanisms of Hg_0.8Cd_0.2Te induced by pulsed TEA-CO₂ laser have been investigated theoretically and experimentally in this paper. The Hg_0.8Cd_0.2Te target was irradiated by a TEA-CO₂ laser with wavelength of 10.6 μm and spike width of 240 ns in an ambient atmosphere. The evident cracks can be found on the surface of the target from the scanning electron microscopy (SEM) photos, indicating that the severe breaks happened during the experiment. Theoretical analysis has also been carried out and the results show that the fracture of Hg_0.8Cd_0.2Te is mainly induced by thermal stresses, although there are three forces (thermal stress, evaporation wave and laser-supported detonation (LSD) wave) exerted on the target surface during the process.     

Study on the Spectrum of Miniature Optically Pumped NH3 Submillimeter-Wave Laser

By means of an iteration method and taking into account the broadening of the infrared pumping laser, the spectrum of a miniature, optically pumped, superradiant NH₃ submillimeter-wave(SMMW) gas laser pumped by CO₂-10R(8) has been calculated and studied by solving density matrix equations. Experimentally, the interferogram of miniature SMMW laser pumped by a TEA-CO₂ laser with 10R(8) line is measured. This is the first time that the theoretical spectrum has been in good agreement with experimental results.     

Injection mode-locking of a 200 joule TEA-CO2 laser

A 200 joule TEA-CO₂ laser has been mode-locked by injection of a nanosecond pulse into a regenerative amplifier operating in an above threshold regime. 25 gigawatt pulses have been obtained.     

Two color oscillations of TE-CO2 laser and applications to two photon process of optically pumped FIR laser

We have developed the resonance system which is able to operate a TE-CO₂ discharge tube in two color emission source. The two color source is excellent in pumping efficiency, spacial overlap and time synchronization of the two emission CO₂ lines.We indicate that the competitive operation of the two emissions is well explained by a simple model.When a TE-CO₂ laser operates at the total pressure of below half atmospheric pressure, we make clear in this work that the operation of a TE-CO₂ laser forms depression like hole burning, with regards to the J of the upper laser level by J-J collisional relaxation during the laser emission.As an example of the two-photon source, two-photon pumping of NH₃ and FIR emissions are given in this paper.     

Experimental study on miniature pulsed CH3OH far-infrared laser

Using a grating tuned TEA-CO₂ laser with 9P(16) line to pump a 10cm or 20cm long miniature Fabry-Perot cavity CH₃OH laser, pulsed far infrared(FIR) lines of 570.6um and 918um wavelengths were observed, the latter is a new line. Operation performance and spectral characteristics of the miniature CH₃OH laser were studied. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

Direct observation of the differences between Raman scatering and population inversion transition for their emission frequencies and pulse waveforms

In FIR laser emissions optically by a CO₂ laser, it has been reported that there are two different process namely induced Raman scattering and population inversion transition.In this paper, we show that the two different process have clearly different characteristics in emission frequensies and pulse waveforms in the case of a TEA-CO₂ laser excitation.We used in this work an intra-cavity etalon for the study of the emission frequensies and also we used a MOM point contact diode for the detection of the wavaformes.Especially, we show that the FIR pulse waveformes are able to analyze numerically on the concept of rate equations.In conclusion, we indicate that molecules would be classified into two categories with regard to optically pumping by a TEA-CO₂ laser. One of them produce mainly Raman scattered emissions, and other produce only the FIR emissions from population inversion transition in spite of high power intensity excitation.     

The tuning characteristics of optically pumped fir cavity laser

Based on the quantum mechanics theory of density matrix and the principle of multiple-beam interference, the tuning characteristics of optically pumped NH₃ FIR lasers were studied. A series of metallic mesh Fabry-Perot cavity lasers with sample tubes of 10cm, 20cm and 100cm in length were constructed and operated successfully, and the FIR laser spectra of the NH₃ cavity lasers pumped by a TEA-CO₂ laser were measured. Supported by the Natural Sciences Foundation of Guangdong Province, PRC     

Infrared and far-infrared laser emissions from a TE CO2 laser pumped NH3 gas

In this paper, infrared (IR) and far-infrared (FIR) laser emissions from a TE CO₂ laser pumped NH₃ gas are reported. 8 IR laser emissions near the wavelength of 12 μm were observed by using 4 different CO₂ laser lines for the pumping. 3 IR laser emissions in P-branch of vibrational-rotational band (ν₂ → G) oscillated simultaneously in two pumping cases, i.e. pumping with the R(30) or R(16) line of 9.4 μm band from the CO₂ laser. 26 FIR laser emissions (26.45 μm ～ 281.0 μm) were observed by using 12 different CO₂ laser lines, and the 10 FIR emissions of them may be new laser emissions as far as we know.     

Fourier-wavelet regularized deconvolution (ForWaRD) for lidar systems based on TEA-CO2 laser

Lidar is an efficient tool for remotely measuring physical quantities or detecting targets. To improve the range resolution in long pulse lidars, such as lidar systems based on TEA-CO₂ lasers, deconvolution methods were used by previous investigators. Deconvolution is a noise sensitive process. In order to avoid noise amplification during the deconvolution process, the Fourier-wavelet regularized deconvolution method is used to deconvolve and denoise the back-scattered lidar signal simultaneously. This method is applied to lidar systems based on the TEA-CO₂ laser and the results are compared to nitrogen tail clipping method. Numerical simulation shows, in comparison to the clipping nitrogen tail technique, by using the ForWaRD method; the range resolution and working distance of the lidar is improved and the clipping tail apparatus is also eliminated.     

Optically pumped high-pressure DF-CO2 transfer laser

Pulsed sealed off CO₂ laser operation at 19 atm gas pressure has been demonstrated by pumping DF/CO₂/He mixtures with radiation from a pulsed DF laser. DF acts as an absorber for the pumping radiation, and the CO₂ upper laser level is populated via subsequent energy transfer. CO₂ pulse energy at 19 atm was 0.5 mJ corresponding to a photon conversion efficiency of 4% measured relative to the number of absorbed pumping photons.     

Nernst effect in Tl-Ba-Ca-Cu-O superconducting films due to infrared laser heating

A Nernst effect has been observed in a high temperature superconductor for the first time. Irradiating superconducting Tl–Ba–Ca–Cu–O thin films by short pulses of a TEA-CO₂ laser, a photovoltaic signal is detected perpendicular to a magnetic field applied parallel to the film surface. The signal is attributed to magnetic flux line depinning and flux line transport driven by the laser induced temperature gradient. The results are described by thermal flux line activation leading to a calculated distribution of pinning energies from 100 K to 4000 K.     

Study of the compounds formed on damaged ZnSe windows by multi-pulse microsecond pulsed TEA-CO2 laser irradiation in air

We report on experimental data of chemical compounds formed in the damaged area at the surface of certain optical ZnSe windows subjected to multi-pulse microsecond pulsed TEA-CO₂ laser irradiation in air. The results are analysed from the viewpoint of implication of the oxidation process activated under the action of CO₂-laser power in plasma initiation and evolution of surface damage process.     

Investigation for long wavelength fir laser lines for EPR studies: New lines from CH2=CF2

The results described in this work are part of a systematic search for long wavelength laser lines to be used in high magnetic field EPR applications and in plasma diagnostic. Four new far-infrared laser lines of CH₂ = CF₂ (1,1 difluoroethylene), optically pumped by a waveguide CO₂ laser, have been discovered and characterized in wavelength, polarization relative to the pumping radiation and offset relative to the CO₂ center frequency. New measurements of polarization and offset of 5 already known laser lines are also reported. A table of all of the known CO₂ pumped FIR laser lines from this molecule is given.     

Operating parameter optimization of optically pumped CH3OH far-infrared laser

By solving the density matrix equations of a quantum system, the output power intensity of an optically pumped CH₃OH FIR laser (CH₃OH-OPFIRL) was calculated by means of iteration method, and the spectral characteristics were got. Base on the calculation, optimization of operating parameters including operating gas pressure, pumped power and output coupling coefficient of the CH₃OH cavity laser were systematically studied. Experimental, a series of FIR emissions of the CH₃OH cavity laser pumped by TEA-CO₂ laser with 9P(16) line were measured. The experimental results were in good agreement with theoretical calculations. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

Diode-pumped continuous-wave Nd:YLF laser at 1313 nm

We present an efficiency Nd:LiYF₄ (Nd:YLF) laser operating at 1313 nm pumped directly into the emitting level ⁴ F _3/2. At the incident pump power of 10.3 W, as high as 3.1 W of continuous-wave output power at 1313 nm is achieved. The slope efficiency with respect to the incident pump power was 36.1%. To the best of our knowledge, this is the first demonstration of such a laser system. Comparative results obtained for the pump with diode laser at 806 nm, into the highly absorbing ⁴ F _5/2 level, are given in order to prove the advantages of the 880 nm wavelength pumping.