FM eliminated CH4locked frequency stabilization of 3.39 µm He-Ne laser in dual feedback control

The frequency of the 3.39 μm He-Ne laser was locked to the CH4saturated absorption line by means of integral-proportional feedback control, i.e., dual feedback control. The frequency modulation was applied by a vibrating mirror placed outside a laser cavity, obtaining a modulation-free laser beam with a stabilized frequency. The long-term stability achieved under integral feedback control was aboutpm1.1 times 10^{-11}, which was further improved topm1.35 times 10^{-12}under dual feedback control. The Allan variance measured by the photomixing technique was1.77 times 10^{-12}at an averaging time 100 s.     

Diffracted light spectroscopy of the 3.39 µm CH4system

A differential analysis of the line shapes of the intracavity saturated absorption peak of methane, observed simultaneously on both the output beam of the laser and on the diffracted beam, points out frequency shifts on the order of several tens of kHz, and also asymmetries of opposite signs. The value and sign of the shift on the principal output beam depends essentially on the cavity geometry. A "critical geometry," analogous to that found for the classical Lamb dip, is proposed for elimination of these important shifts related to the Gaussian character of the beams and for obtaining symmetric line profiles.     

Continuous-wave CH3F waveguide laser at 496 µm: Theory and experiment

The kinetic processes controlling the conversion of CO2pump radiation into far-infrared (FIR) radiation in optically pumped waveguide lasers are discussed. It is found that pump saturation and excited-state FIR absorption play major roles in limiting the conversion. Good agreement between theory and experiment was obtained over a wide range of pump powers, gas pressures, and mirror reflectivities. For a well-optimized system, power-conversion efficiencies of 0.2-0.6 percent can be realistically achieved for CH3F.     

New laser lines with wavelengths from λ = 61.7 µm down to λ = 27.7 µm in optically pumped CH3OH and CD3OH

25 new CW far infrared laser lines have been observed with wavelengths fromlambda = 61.7 mum down tolambda = 27.7 mum. We have significantly increased the number of known short wavelength laser lines and extended the laser line spectrum to the 30 μm region by using a BaF2outcoupling system.     

Infrared transmission at the 3.39 µm helium-neon laser wavelength in liquid-core quartz fibers

Measurement of optical transmission loss at the 3.39 μm line of an He-Ne laser in a tetrachloroethylene (C2Cl4)-filled fused-quartz fiber is reported. The loss is found to be 56 dB/km at this wavelength.     

Simple technique for the detection of oscillation at 3.39 µ in a He-Ne laser operating at 632.8 nm

A simple technique is reported for determining if oscillation is occurring simultaneously at 3.39 μ and 632.8 nm in a He-Ne laser. It relies on observation of modulation of the output power at 632.8 nm when a variable path length element is introduced into the optical cavity of the laser. The technique is applicable to other gas laser systems where competition for upper level populations occurs between transitions at widely differing wavelengths.     

Continuous wave 16 µm CF4laser

A 16 μm CF4laser oscillator has operated continuous wave in a cooled static cell. Pump powers required from the low-pressure continuous wave CO2laser were approximately 3 W. The laser cavity was a multiple-pass off-axis-path two-mirror ring resonator. Unidirectional CF4laser power at 615 cm^-1exceeded 2 mW. Rate equations were used to estimate scaling of this laser source. For modest pump powers (40 W) approximately 1 W of emission power is predicted from this small and simple system.     

Polarization-Dependent gain saturation and nonlinearity-induced anisotropy in the 3.39-µ He-Ne laser amplifier

Polarization dependence of the nonlinear behavior of a high-gain strongly saturated 3.39-μ He-Ne laser amplifier is experimentally investigated. It is found that while circularly and linearly polarized signals propagate through the medium with their polarization unchanged, elliptically polarized signals undergo a change of eccentricity. In addition, the nonlinear gain depends on the input polarization: saturation is strongest for circular and weakest for linear polarization. Excellent agreement is found between the experiment and theoretical predictions.     

Efficient acoustooptic modulation at 3.39 and 10.6 µm in crystalline germanium

A Ge acoustooptic pulse modulator has been constructed and tested at 3.39 and 10.6 μm. A pulse rise time of 20 ns and deflection efficiency of 11 percent per watt of RF drive power when operating at 10.6 μm were realized.     

He-Ne laser frequencies near 2.4 µm and their application to hydrogen fluoride detection

He-Ne lasers can provide three frequencies near 2.4 μm, one of which coincides with the1R(5)frequency of HF at 4173.98 cm^-1. Either of the other frequencies may serve as a reference for absorbance measurements. One of these, at 4169.33 cm^-1, is a new lasing transition not previously observed (4d'_{4}-3P_{9}). Operating conditions are discussed.     

Distributed feedback laser emitting at 1.3 µm for gigabit communication systems

A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.     

Spectral linewidth estimation of a 1.5 µm range InGaAsP/InP distributed feedback laser

Spectral linewidth of a 1.5 μm range distributed feedback buried heterostructure (DFB-BH) laser in CW operation is estimated theoretically and experimentally. Considering the equivalent mirror facet loss coefficient and the confinement factor in the active layer, etc., we modified the conventional formula for the spectral linewidth of single-mode semiconductor lasers and presented a formula for the linewidth of DFB lasers. Furthermore, power-dependent linewidth measurements of a 1.5 μm range InGaAsP/InP DFB-BH laser with a window region were carried out using Fabry-Perot interferometers. The linewidth was observed to increase linearly with inverse output power. The measured result was explained by the calculated result through the modified formula. The full width at half maximum was estimated to be 50 MHz at an output power of 1 mW.     

1.5 µm range InGaAsP/InP distributed feedback lasers

Lasing characteristics of InGaAsP/InP distributed feedback (DFB) lasers in the 1.5 μm range were studied theoretically and experimentally. Wave propagation in five-layer DFB waveguides were analyzed to estimate the effect of the structural parameters on threshold conditions. A brief consideration on designing a low threshold laser and its lasing wavelength was made. DFB buried heterostructure lasers with fundamental grating emitting at 1.53 μm were prepared by liquid phase epitaxial techniques. CW operation was confirmed in the temperature rangeof -20° to 58°C, and a CW threshold current was as low as 50 mA at room temperature. A stable single longitudinal mode operation was observed both in dc condition and in modulated condition by a pseudorandom pulse current at 500 Mbits/s. No significant increase in the threshold current was observed after 1400 h continuous CW operation at 20°C.     

A 10.6 µm scan laser with programmable VO2mirror

A scan laser controlled by the variable reflectance of a VO2film on a CRT faceplate has been demonstrated at 10.6 μm. The cavity is a flat field conjugate resonator with an active medium of axially flowing CO2-N2-He gas mixture. The output beam has been scanned in a circular pattern at 20 Hz. Output modulation has been observed at a raster frame rate of 45 Hz (100 percent) and at a raster line rate of 4.44 kHz (< 100 percent).     

基于温度闭环反馈的He-Ne激光器热稳频系统

为了提升激光回馈测量系统中He-Ne激光器的性能, 解决激光回馈镜不断移动时频率无法使用传统方法稳定的技术问题, 采用基于温度反馈控制激光器管体温度的闭环被动稳频的方法, 进行了理论分析和实验验证, 研究了不同管体温度与环境温度差值下频率稳定性。结果表明, 系统最佳温差为25.6℃; 在此温差条件下稳频后, He-Ne激光器波长波动范围达10-4, 即频率稳定性达到1.61×10-7, 功率漂移量低于3.20%。该系统可以根据环境温度的变化调节稳频温度点, 并且稳频结构简单, 满足激光回馈一般应用系统稳定性的要求。     

Saturation of hot CO2by short 10.6 µm laser pulses

Saturation of the absorption of hot CO2by 1.6 nsP(18)andP(20)laser pulses at 10.6 μm has been measured. Coherent propagation calculations with no fitting parameters are in good agreement with the data and are consistent with a substantial hot-band contribution to theP(20)saturation.     

Performances of a frequency offset locked He-Xe laser system at 3.51 µm

A highly stabilized frequency offset locked He-Xe laser system was constructed for high resolution laser spectroscopy of H2CO [5_{1,5}(upsilon = 0) rightarrow 6_{0,6}(upsilon_{5}= 1)] at 3.51μm. It is composed of three He-Xe lasers. The first laser is H2CO-stabilized and is used as a frequency reference in the system. The second laser is frequency offset locked to the first laser by using the beat frequency between these lasers, and is used as a local oscillator. The third laser is frequency offset locked to the second laser, and is used to observe the H2CO spectrum by slowly varying the beat frequency between these lasers. The frequency stability of the first laser, measured against a similarly stabilized and synchronously modulated laser, was1.0times10^{-14}attau = 100s, where τ represents the integration time. The frequency traceability of the second laser to the first laser was expressed as8.0times10^{-13} cdot tau^{-1}for 10 msleq tau leq 100s. It was found that this value of the traceability was independent of the frequency modulation of the first and second lasers. The frequency traceability of the third laser to the second laser was nearly equal to that of the second laser described previously. The variable range of the frequency of the third laser was 19 MHz. In this range, the frequency traceability of the third laser to the second laser was independent of the beat frequency between these two lasers. From these results, it was concluded that this system can be used for the observation of the H2CO spectrum.     

Direct demodulation of a 10.6µm FM signal with an NH2D stark cell

A new technique for direct demodulation of a 10.6-μm FM signal using a Stark absorption cell is described. A Stark tunable absorption line in NH2D is used to track the time-varying frequency of the incoming FM laser signal using a closed servo loop. The demodulated FM signal is proportional to the feedback voltage applied to the Stark cell. Demodulation at frequencies up to 5 kHz has been demonstrated, the rate being limited only by the bandwidth of the available servo electronics.     

Amplifying medium characteristics in optimized 190 µm/195 µm DCN waveguide lasers

Extensive study of the CW, dischaxge-pumped, DCN laser operating on the (22⁰0-09¹0) 190 and 195 μm lines has been undertaken in order to develop a new source of radiation suitable for plasma diagnostics. The optimum values of the parameters of the discharge, the unsaturated gain, and the saturation intensity are given as a function of the tube diameter. Scaling laws predicting the maximum output power as a function of the tube dimensions and of the cavity loss are established. Such lasers compare favorably with optically pumped submillimeter lasers, since 250 mW are available from a 3 m long, 5 cm diameter waveguide DCN laser.     

Stimulated emission at 2.04 µm in Ho3+-doped ErVO4and YVO4

We have observed both CW and pulsed laser operation in Ho³⁺-doped ErVO4and YVO4at 2.0416 μm and 2.0412 μm, respectively. Both laser emissions are linearly polarized. For this preliminary experiment the crystals were cooled to liquid nitrogen temperature and pumped in two configurations using an argon-ion laser and a xenon flashlamp.