A system for measuring absolute frequencies of up to 4.25 THz using a Josephson point contact

A system for measuring the absolute frequency of a far-infrared (FIR) laser is described. Josephson point contacts have been utilized in the system as a frequency harmonic mixer connecting microwaves and optically pumped CH₃OH laser lines. The Josephson point contacts are capable of generating beat signals of 90 GHz microwaves and FIR waves of up to 4.25 THz. To measure the frequency of the beat signals from the Josephson junction with a frequency counter, tracking oscillators have been developed, which tracks the beat signals by phase locking and regenerate clean signals for frequency counting. It is shown that the absolute frequency can be measured to an accuracy of about 100 Hz by using the tracking oscillators.     

Torsional refilling transitions in tea-pumped CH3OH fir lasers with associated high-resolution fir spectra

It is proposed that a number of the high-frequency far-infrared (FIR) laser lines observed when CH₃OH is optically pumped by high-power CO₂ TEA lasers can be identified as refilling torsional transitions within the vibrational ground state. Assignments are presented for 8 such TEA-pump/FIR-laser refilling systems. To provide support for the assigned laser frequencies, high-resolution Fourier transform FIR spectra of CH₃OH have been obtained and partially analyzed in the torsional transition region.     

Assignments and predictions of far-infrared laser lines in methyl alcohol

In this work, the results of detailed spectroscopic analyses of the high-resolution Fourier transform infrared (IR) C-O stretch and far-infrared (FIR) torsion-rotation bands of methyl alcohol are applied to assign and predict FIR laser lines optically pumped by a CO₂ laser in the dense Q-branch region of the C-O stretch band. The assignments are supported by means of closed combination loops of accurately measured transition frequencies. For the predicted FIR lines, the frequencies are deduced with an accuracy of ±0.001 cm⁻¹, which is at least an order of magnitude better than can be obtained from direct wavelength measurements. The IR and FIR spectroscopic data relevant to the assignments are included.     

The optimum pumping power for optically pumped FIR lasers

The relations between the output power of optically pumped FIR laser and the pumping power were studied theoretically by solving the density matrix equation of four-level system by means of the matrix signal flow graph method. The output power density of FIR laser was calculated by iteration method. A set of curves of output FIR power density against pumping power has been obtained. It has found that every of each curve has a maximum point of which the position is different for different pumping detuning. According the these results we predicted that there would exist an optimum pumping power density for an optically pumped FIR laser with certain pumping detuning. This theoretical results would help us to design the optically pumped FIR lasers.     

光泵NH3分子远红外激光研究

运用量子系统的密度矩阵理论，采用迭代法计算了光泵ＮＨ３分子远红外超辐射和腔式激光的频谱特性和相应的最佳工作气压。理论计算表明相对于超辐射方式，光泵腔式ＮＨ３分子远红外激光具有宽带辐射以及纵向调谐特性，且总的输出光强在一定条件下得到提高，最佳工作气压也较低。在实验上对ＴＥＡＣＯ２－１０Ｒ（８）和９Ｒ（１６）泵浦的Ｎ 红外超辐射和腔式激光器产生的远红外辐射进行了测量。结果表明理论计算与实验结果相符。     

Diffusion of excited state molecules in FIR- and CO2-lasers

Both standing waves in laser oscillators and spatially inhomogenous cross sections of laser beam and pumprate cause a non-uniform distribution of excited state molecules in longitudinal and transversal direction, respectively. This spatial hole burning however is smoothed by diffusion of the excited molecules. The effect of diffusion is investigated theoretically for an optically pumped far infrared laser as well as the corresponding CO₂ pump laser. It is found, that the remaining spatial hole burning in the direction of wave propagation is negligible within CO₂ lasers but not within FIR lasers. Concerning the transversal direction it can be shown that in the FIR laser diffusion takes no effect, whereas the transversal distribution of the excited molecules in the CO₂ laser is significantly influenced by diffusion.FIR ring lasers avoid longitudinal spatial hole burning, which leads to the common assumption that they use the active medium more efficient than conventional standing wave lasers, hence delivering higher output powers. This expected advantage is levelled out to a great extent by diffusion.     

Pulsed optically pumped far infrared laser and maser action in OCS

Twenty new optically pumped far-infrared laser transitions have been observed in OCS, including four “maser” transitions of 3.6–8.2 mm wavelength. The operating conditions and assignments of these lines are reported. Rabi splitting of the FIR gain profile caused by the high intensity of the CO₂ TEA laser pump is found to be very important for some lines.     

Spectra of optically pumped superradiant and cavity NH3 far-infrared laser

Based on the density matrix theory of quantum system, the spectra of optically pumped superradiant and cavity NH₃ far-infrared (FIR) lasers were calculated by means of iteration method. The calculation showed that, compared with the optically pumped superradiant FIR laser, the cavity laser had a wider band spectrum of FIR emission and a higher output power under certain condition, moreover, the spectra of cavity laser had multi longitudinal-mode structure. Supported by the Research Foundation of Hubei Province Education Committee, PRC     

Continuous-wave room-temperature operation of a 2.8 μm GaSb-based semiconductor disk laser

We demonstrate an optically pumped semiconductor disk laser based on the (AlGaIn)(AsSb) material system, which operates at an emission wavelength of 2.8 μm. Up to 120 mW of output power were obtained in cw operation and more than 500 mW in pulsed mode. The performance of the present laser is discussed in comparison to shorter-wavelength semiconductor disk lasers based on the same materials system.     

Emission spectra of the tunable Raman CH3F optically pumped fir laser

The six-level model using a density matrix approach to simulate properties of a gas resorant media in optically pumped FIR lasers was developed. The model accounts for multiphoton as well as parametric processes. Advantages of the developed model are demonstrated by calculation and discussion of the gain and saturated emission spectra of CH₃F laser when transitions with different J rotational numbers of CH₃F are pumped.     

Application of the opto-acoustic effect to the operation of optically pumped far-infrared gas lasers

A method is reported which allows the operation of optically pumped farinfrared (FIR) gas lasers in a simple way: A spectrophone is used to control and to stabilize the pump laser frequency in order to achieve most efficient optical pumping of the FIR laser gas.     

High-sensitivity intracavity laser absorption spectroscopy with vertical-external-cavity surface-emitting semiconductor lasers

We report the demonstration of high-sensitivity intracavity laser absorption spectroscopy with multiple-quantum-well vertical-external-cavity surface-emitting semiconductor lasers (VECSEL's). A detection limit of 3x10(-10) cm (-1) has been achieved. The spectrotemporal dynamics of a VECSEL in the 1030-nm wavelength region has been studied. The laser was operating cw at room temperature, with a baseline signal-to-noise ratio as high as 400. The laser was optically pumped with a threshold as low as 80 mW and was broadly tunable over a spectral range of ~75 nm .     

碟型量子阱微腔激光器的低阈值激射

利用反应离子刻蚀(RIE)和湿法腐蚀方法在InGaAs/InGaAsP多量子阱材料上研制出直径为8μm、4.5μm和2μm的碟型半导体微腔激光器。其中2μm直径的微碟在液氮温度下其光泵浦激射阈值仅为3μW左右。对高光功率密度下泵浦时出现的多模激射、跳模和激射光谱强度饱和现象进行了研究。并对微碟激光器的激射光谱线宽特性进行了初步的分析。     

Spectral Characteristics of Raman Emissions from Miniature Pulsed Optically Pumped Far Infrared Laser

A miniature FIR laser with a sample-tube in 10 or 20cm length were constructed, and the laser's cavity consisted of a pair of metallic meshes, with NH3 molecules as active medium pumped by a TEA-CO2 laser, a series of FIR laser lines were observed. By taking account of the properties of the Fabry-Perot cavity and the gain characteristics of Raman transitions in the miniature optically pumped FIR laser, the spectral characteristics of the FIR laser were studied.     

Characterization and frequency measurement of a new far infrared laser line from CHin2Fin2

We present the discovery and frequency measurement of a new FIR laser line from CH₂F₂ optically pumped by a waveguide CO₂ laser. This new line has the same CO₂ laser pump line (9R32), offset (+5 MHz) and relative polarization of the strongest FIR laser line of CH₂F₂, namely the 184.3μm. The frequency is only 19,454 MHz apart from that of this line. We got a frequency measurement of 1,646,196.6 (10) MHz, which corresponds to a wavelength of 182.112 μm.     

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     

New Optically Pumped FIR Laser Lines and Frequency Measurements from CH3OD

This work reports the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH₃OD in the range 42.6 m to 207.2 m. A highly efficient CO₂ laser was used as the pump laser for an Optically-pumped Fabry-Perot FIR laser. The frequencies of most of the new lines were measured in the range 1.7 to 6.4 THz. Twenty-eight CO₂ lines were used as pump lines; nineteen of these had frequencies lower than those previously used to pump CH₃OD in a FIR laser. Sixteen of the new FIR lines had absorption transitions which belong to the OD bending vibrational mode.     

High‐brightness long‐wavelength semiconductor disk lasers

A review on the recent developments in the field of long‐wavelength (λ >1.2μm) high‐brightness optically‐pumped semiconductor disk lasers (OPSDLs) is presented. As thermal effects have such a crucial impact on the laser performance particular emphasis is given to modelling the thermal behaviour and optimisation of the heat‐sinking. Selected OPSDL devices, realized in different III‐V and IV‐VI semiconductor material systems, with corresponding emission wavelengths between 1.2 μm and 5.3 μm are presented. Specific applications in this broad spectral range are addressed and methods to obtain high output power are discussed in terms of the underlying material properties and device operating principles.     

用于定向红外对抗的中波红外激光器技术

针对定向红外对抗系统对中波红外激光器在激光波段、激光功率、激光束散角、激光重复频率以及调制波形等方面的具体要求,通过对光泵半导体激光器、量子级联激光器和基于光学参量振荡的固体以及光纤激光器的技术特点与发展现状的分析比较,和对双折射相位匹配与准相位匹配的特点和最新发展动态的梳理,提出用高功率高光束质量的1 064 nm固体激光器或光纤激光器泵浦基于掺氧化镁的周期极化铌酸锂晶体（PPMgLN）的光学参量振荡器的中波红外激光器方案,其波段转换效率可达到16%以上。     

Laser induced line narrowing and saturation broadening effects in OPFIRL

The variation of the laser linewidth within an optically pumped NH3 FIR laser has been studied theoretically on the basis of three-level quantum system approach. It has been shown that the activated medium within the sample tube of an optically pumped ASE FIR laser can be divided into three regions: A). Laser induced line narrowing region, in which the FIR laser linewidth is less than Lorentz linewidth; B). Saturation broadening region, in which the power density of the FIR. signal becomes large enough to make saturation effect important and the linewidth broadens; C), Self-absorption narrowing region, in which the pumping energy density is below the threshold, so self-absorption dominates and the linewidth decreases. The necessary linewidth of the OPFIRL can be obtained by appropriate selection of the length of the sample tube.