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.     

Quantum mechanical features of optically pumped CW FIR lasers

Quantum mechanical predictions for the gain of an optically pumped CW FIR laser are presented for cases in which one or both of the pump and FIR transitions are pressure or Doppler broadened. The results are compared to those based on the rate equation model. Some of the quantum mechanical predictions are verified in CH3OH.     

A powerful new optically pumped FIR laser--Formylfluoride

Intense FIR laser action is reported in formylfluoride (HFCO) with 7 lines of the normal CO2laser and 4 lines of the C¹⁸O2laser.     

Relaxation oscillations in optically pumped molecular lasers

We report the observation of relaxation oscillations in both the C¹³H3F and C¹²H3F optically pumped lasers. Expressions are derived for the oscillation frequency and its temperature and pressure dependences using a four-level rate equation model. We observe excellent agreement between measured frequencies and the theory presented. Models are considered for using this phenomenon to determine the rotational and vibrational relaxation mechanisms of the laser gases.     

寻求光泵FIR激光器工作物质的一种方法

用“双基团振动”和“直线型三基团振动”的物理模型解释了已有光泵FIR激光器的工作机理,并由此得到了寻求光泵FIR激光器工作物质的一种方法。     

High-power operation and scaling behavior of CW optically pumped FIR waveguide lasers

High-power far infrared (FIR) laser operation at the 10- 100 mW level is described for wavelengths throughout the 40 μm-1.22 mm spectral region. These data correspond to order of magnitude improvements in converting CO2laser energy into FIR laser output. This improved FIR laser performance is attributed to a waveguide laser geometry with reduced losses for the CO2pump and also to a new method of output coupling. The basic design concept of the efficient laser resonator is discussed as well as the prospect for further increases in laser performance through improved efficiency and sealing.     

New optically pumped far-infrared lasers

Ninety-seven new far-infrared (FIR) laser transitions have been observed in optically pumped ethylene glycol, dimethyl ether, formic acid, and monomethyl amine, all excited by a pulsed CO2laser.     

Instabilities in optically pumped infrared lasers

The unstable emission of an optically pumped FIR gas laser is theoretically analysed through numerical resolution of the associated Maxwell-Bloch equations. The instability domain in the main control parameters space is determined and an example of chaotic behaviour is examined.     

Tunable optically pumped GaAs-GaAlAs distributed-feedback lasers

A new wavelength tuning effect in optically pumped GaAs-GaAlAs distributed-feedback lasers is presented. It is shown that it is possible to tune the emitted wavelength of the laser by changing the angle between the direction of the pumping line and the normal to the grooves of the periodic structure. The results could be applied to injection DFB lasers to achieve frequency multiplexing for optical communications.     

Theory of optically pumped submillimeter lasers

Theoretical models of the operating characteristics of both pulsed and CW optically pumped submillimeter (SMM) lasers are reviewed. The SMM laser gain is discussed for both pressure and Doppler broadened transitions. A review is given of expressions for SMM laser gain based on quantum mechanical calculations in a three-level molecular system.     

Stability of single-mode optically pumped lasers

We study mode competition in optically pumped lasers with one active laser line. The stability of single-mode operation under one mode pumping (both fields arbitrarily intense) is determined by calculating the saturated laser gain using either a mono- or bichromatic probe. The probe spectra differ dramatically from the single-mode, intense field gain curves occasionally exploited in this context in earlier works. Some features in the spectra are interpreted with the dressed atom picture. The mathematically simpler single probe gain is shown to be a good approximation for large mode spacings. When the strong field induced Rabi flipping is comparable to the mode spacing, however, a bichromatic probe containing two frequencies which are symmetric with respect to the intense mode is usually needed. Typical mono- and bichromatic probe spectra are discussed and parameter regions are explored which give stable single-mode operation. The results are also relevant in general laser instability studies: some aspects due to the strong field induced coherences will be pointed out.     

Three-photon contributions in optically pumped lasers

A signal flow graph representation of the density matrix equations appropriate to a serial three-wave interaction is introduced, from which perturbation theory and AC Stark shift information may be extracted. The conditions for a large interaction cross section for the three-photon transition are deduced and applied to selected experimental situations with the main conclusion being that the effect may be present in a large number of CW and pulsed experiments.     

Diffraction limited CW optically pumped lasers

The far infrared spectral characteristics of inductive metal mesh dielectric hybrid mirrors were investigated. From experimental and theoretical studies, the mirrors were found to exhibit etalon effects due to the finite Si substrate thickness and to have two separate diffraction conditions. With grid spacinggand substrate index of refractionn, forn^{-1} < g/lambda < 1the mirrors diffract in transmission while forg/lambda > 1the mirrors diffract both in transmission and reflection. Using both inductive and capacitive mesh mirrors, EH11outputs have been obtained at the milliwatt level in the range 70 μm to 1.2 mm. Powers in excess of 10 mW were obtained from CH3OH at 96 and 118 μm, HCOOH at 393 μm, CH3I at 447 μm, and CH3F at 496μm.     

The optically pumped hydrazine FIR laser: Assignments and new laser lines

Strong far-infrared (FIR) lasing action has been observed in hydrazine optically pumped with isotopic CO2lasers and the N2O laser. The wavelengths of 13 new laser lines have been determined. The results of a recent infrared-microwave double resonance study of hydrazine have been used to assign the transitions involved in the production of five of these new lines and nine of the previously observed laser lines.     

A new stabilization system for optically pumped cw far infrared lasers

A new type of stabilization system for optically pumped far infrared (FIR) lasers based on a dual modulation technique is described, which enables to control the laser output power both as a function of the CO₂-laser pumping frequency and the FIR laser cavity length. The system greatly improves the laser output stability and causes only a negligible modulation (<1 %) of the output power. An additional feature, an electronic search circuit for emission lines, simplifies working at the laser even by ineperienced people.     

FM-noise measurements on an optically pumped FIR laser

We report the noise measurements performed on a synthesized signal at 761 GHz starting from a 5 MHz quartz oscillator, as well as the investigation of the frequency noise of an optically pumped FIR laser and the possible origin of this noise. Bandwidth requirements for phase-locking an FIR laser are obtained.     

Injection locking of an optically pumped FIR laser

Phase locking of optically pumped far-infrared lasers to highly stable synthesized signals is an interesting goal, at least for metrological purposes. In this paper, the possibility of obtaining such a stabilization by injection of the reference signal into the laser is investigated, and from the results obtained, it is inferred that this technique can be efficiently used in the frequency range up to 1 THz.     

A review of optically pumped NMMW lasers

Near-millimeter-wave (NMMW) gas lasers, which are optically excited with a CO2pump laser, are currently the major sources of coherent radiation in the NMMW region (100 to 1000 GHz). These molecular sources are especially useful at NMMW frequencies > 300 GHz where conventional millimeter-wave sources have serious disadvantages. Optically pumped NMMW lasers can provide tens of milliwatts of CW power of very high spectral purity or megawatts of pulsed power with a broader spectral bandwidth. The state of the art of these lasers, with an emphasis on CW operation, is reviewed. Included are discussions of basic principles of operation, design, and approaches to building laser systems with sufficient power and stability for useful application. Some of the uses of NMMW lasers and some current research efforts on these sources are described.     

Two-photon transitions in optically pumped submillimeter lasers

The emission frequency of an amplified spontaneous emission (ASE), optically pumped submillimeter (SMM) laser has been studied as a function of laser gas pressure for several different gases and SMM laser lines. For off resonant pumping, Fabry-Perot interfetometer scans indicate a shift in emission frequency between high- and low-pressure laser operation. In high-pressure operation, emission occurs via a Raman type, two-photon process with some additional frequency offset due to the ac Stark effect. The Raman process is favored by its higher quantum efficiency over a two-step process involving single-photon transitions at the pump and SMM wavelengths. In low-pressure operation, the SMM laser emission is found to be delayed in time with respect to the pump pulse. The Raman process thus cannot occur and the two-step process is favored. This results in a shift in the SMM laser emission frequency from the Raman line to the line center frequency of the SMM laser transition. The Raman emission gain bandwidth appears to be broadened by the CO2pump laser bandwidth.