New CW FIR laser action by Stark tuning from optically pumped CH3OH and CH3OD

Fifteen new CW FIR laser lines are reported from Stark tuned CO2optically pumped CH3OH and CH3OD. Four new CW laser lines have also been observed from zero field optically pumped CH3OD, three with a CO2laser, and one with an N2O laser.     

Resolution of sidebands in a semiconductor laser frequency modulated by ultrasonic waves

Frequency modulatlon or a semiconductor laser via ultrasonic waves is achieved at a modulating frequencyomega_{m} - 150MHz for CW operation at 4.2°K. Individual sidebands are resolved whose variation with pressure agree well with theory, indicating that little distortion is present. A modulation index of 6 is achieved corresponding to a frequency deviation of 900 MHz and an acoustic pressure of 3 atmospheres. Under pulsed operation at 4.2°K and 77°K frequency modulation is observed as a blurring of the laser frequency.     

Effect of nitrogen on XeF(C→A) and Xe2Cl laser performance

Experiments demonstrating the effect of nitrogen on electron-beam pumped XeF(C rightarrow A) and Xe2Cl laser performance are reported. The laser power of the XeF(C rightarrow A) laser decreased with increasing nitrogen pressure, whereas the Xe2Cl laser power increased by a factor of three at an optimum nitrogen pressure of 200 torr. Atomic absorptions in both laser spectra are decreased by the addition of nitrogen. The kinetic mechanisms leading to the observed behavior are discussed.     

Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH3OH pumped by theS-9P(31),18-10R(24),13-9R(26), and13-9P(16)CO2laser lines, plus an interesting speculation for the FIR line pumped by the18-9P(12)CO2line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm^-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three¹⁶O¹²C¹⁸O laser lines.     

Theoretical and experimental studies of a multiline TEA CO2laser with hot CO2as an intracavity absorber

The multiline behavior of a ballast resistance helical TEA CO2laser incorporating hot CO2as an intracavity absorber has been studied. Simultaneous laser oscillation onP(16), P(18), andP(20)lines of 10.6 μm has been obtained reliably. A rate equation model has been developed for the hot CO2absorber and is incorporated with the model for the multiline TEA CO2laser for calculating laser intensities onP(16), P(18), P(20), andP(22)lines of the 10.6 μm band in the presence of the absorber. The theoretical calculations agree quite well with the experimental observations. These studies show that a hot CO2column of Proper length and temperature inside a TEA CO2laser cavity can produce simultaneous laser oscillation on at least three rotational linesP(16), P(18), andP(20)of the 10.6 μm band with almost equal intensity.     

Investigation of D2O-laser emission at 50, 66, 83, 111, and 116 µm

A D2O laser oscillator axially pumped by a TEA CO2laser operating on the9P(32)line has been investigated. The laser emits five FIR lines whose emission characteristics are presented. For the three strongest lines (66, 111, and 116 μm) and an oscillator of length 45 cm, a single axial mode can be made to dominate. Special attention is drawn to the newly discovered and identified 111 μm line.     

Characteristics of a Raman laser excited by an ordinary ruby laser

The stimulated Raman effect of benzene has been observed using an ordinary (nongiant) ruby laser. The build-up of oscillation at the v2, 2v2, 3v2and 4v2Stokes lines and also at the first v1Stokes line have been observed. The threshold exciting power for laser action in the v2Stokes line has been measured to be 9.5 kW. A rate equation for the Raman laser has been given, and the total scattering cross section for the v2Raman line of benzene has been determined as σ = 0.46×10^-28cm². The estimation based on the results of this investigation indicates that it is possible to construct a Raman laser of benzene using an Ar gas laser.     

Optically pumped submillimeter wave laser with Michelson interferometric output coupling

We report the performance of an optically pumped submillimeter wave laser incorporating a Michelson interferometric output coupler consisting of three mirrors and a metal mesh beam splitter. 10.33-μm radiation from a pulsed CO2TEA laser was used to pump NH3for generating submillimeter wave radiation at 281 μm. Optimum output was achieved by coupling out 59 percent of the radiation per pass using a 250-lines-per-inch mesh at a phase angle of 49°. The submillimeter laser operated in the TEM00mode and was tunable over its free spectral range of about 350 MHz. Translation of the coupling mirror allowed optimization of laser output.     

Plasma chemistry of the closed-cycle 1 kHz transversely excitedatmospheric CO2 laser with an efficient catalytic CO2 regenerator

A high-power closed-cycle 1 kHz transversely excited atmospheric (TEA) CO₂ laser with an efficient catalytic CO₂ regenerator was used to investigate the variations of the average laser output power and the concentrations of the CO₂, CO, and O₂ molecules in the laser gas mixture with the operational performance of the CO₂ regenerator. It was experimentally shown that for the laser gas mixture of CO₂-N₂-He=15-15-70% and the output coupler reflectivity of 70%, η of 0.1 was required to maintain the laser output power greater than 90% of the initial laser output power of 570 W at an input energy density and a clearing ratio of 150 J/L and 3.0, respectively     

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.     

A two-wavelength, passively self-injection locked, CW Ti3+:Al2O3 laser

We have demonstrated that passive self-injection control is very effective in a CW Ti³⁺:Al₂O₃ laser to produce high efficiency (η~15%), narrow-line, two-wavelength emission. Light reinjection is achieved with an original high-resolution two-wavelength selector combining an interference wedge and a grazing incidence grating. The device operates outside the main nonselective laser cavity; thus avoiding insertion losses and optical damage problems. A 1.5 W, background free, total output power has been obtained simultaneously at two narrow laser lines (fwhm: 8 pm), independently tunable over 50 mn. The two laser lines can be emitted in a single beam or in two separated beams. Self-injection wavelength control has been demonstrated both for linear and for ring laser cavities. In the latter case, unidirectional behavior is also obtained in the same way. Single-step (5s²S_1/2-5P²P_1/2,3/2 ) and two-step (5s²S_1/2-5p²P_3/2-5d² D_3/2,5/2) excitation of atomic rubidium vapor has been performed with our original laser device     

A theory of the mode-locked, internally frequency-doubled laser

An AM mode-locked laser with a frequency doubler internal to the laser cavity is analyzed. Mathematical expressions are derived for laser pulsewidth, saturated gain, and second-harmonic output power. It is shown that the maximum second-harmonic power output available from the mode-locked laser is a factor ofsqrt{2}less than that available from an identical free-running laser. Numerical examples are given for an Nd:YAG laser with a Ba2NaNb5O15internal frequency doubler.     

Far-infrared laser gain resulting from rotational perturbations

A simplified model is used to calculate the unsaturated gains of far-infrared rotational and vibrational-rotational laser transitions that are caused by rotational perturbations. Inversions are derived from the perturbation of an initial Boltzmann distribution of rotational populations, permitting the calculation of laser gains in terms of the perturbation parameters and the vibrational populations. The gain equations are applied to the three perturbations of H2O¹⁶that result in the largest number of laser lines. Numerical gain values in good qualitative agreement with experimental results are obtained.     

Efficient operation of a low-impedance Blumlein discharge initiated HF/DF chemical laser

A study is described on the efficient operation of an HF/DF chemical laser initiated by a low-impedance Blumlein discharge. Some combinations of 0.33 and 0.66-Ω flat-plate Blumlein lines with simple discharge chambers of various active volumes were investigated. For an SF6/H2mixture, an HF laser gave a maximum efficiency of 6.3 percent, and 5 J/1 was extracted. Substitution of D2for H2gave a DF laser output energy as high as 80 percent of the HF chemical laser output.     

Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser

A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds⁴I9/2in Nd³⁺,⁴I15/2in Er³⁺,⁵I8in Ho³⁺and³H6in Tm³⁺. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the⁴F3/2-⁴I9/2transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.     

Sn–Ag–Cu Soldering Reliability as Influenced by Process Atmosphere

To develop an optimal surface mount reflow soldering process with Sn–Ag–Cu, the influences of atmosphere and cooling speed on soldering reliability have been examined by using Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB). Typical three Sn–Ag–Cu alloy pastes, i.e., Sn–3.0wt%Ag–0.5wt%Cu, Sn–3.8wt%Ag–0.75wt%Cu, and Sn–4.0wt%Ag–0.9wt%Cu, were used for reflow soldering in air or ${hbox {N}} _{2}$ atmospheres. In the case of chip component joints, the solder compositions, cooling speed, and atmospheres during reflow treatment slightly affect the dendritic microstructure of the solder fillets. In contrast, these parameters rarely affect the solder wettability both on boards/components and shear strengths of the solder joints. In the case of the SOP joints, however, the atmospheres in reflow treatment and the fluxes strongly affect the appearances of solder fillet surfaces structure. Despite the types of solder fluxes, ${hbox {N}} _{2}$ process atmosphere obviously improved wettability of the solders on the lead-frames of the SOP. Moreover, the scatter in shear strengths becomes smaller and the wetting of solders on the lead-frames becomes stabler in ${hbox {N}} _{2}$ atmosphere than in air atmosphere.      

CO2laser annealing of Si3N4, Nb2O5, and Ta2O5thin-film optical waveguides to achieve scattering loss reduction

Significant reductions in the optical scattering losses of Si3N4, Nb2O5, and Ta2O5waveguides fabricated on SiO2/Si substrates have been measured following CO2laser annealing. The largest improvements were observed for Si3N4waveguides, where waveguide attenuation values of about 6.0 dB/cm before laser annealing were reduced to as low as 0.1 dB/cm afterwards. An improvement of more than an order of magnitude was obtained for a Nb2O5waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb2O5waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta2O5waveguide was found to decrease from 1.3 dB/cm before laser annealing to 0.4 dB/cm afterwards. In the case of a thermally oxidized Ta2O5waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.     

Optical power limiting and stabilization based on a novel polymercompound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by ~810 nm and ~7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d₀=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the ~810-nm laser beam is increased from I₀=15 to 600 MW/cm² . The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I₀≈400 MW/cm² with a Δ≈±25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to Δ≈±8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are σ₂=66, 80, and 101×10^-20 cm⁴/GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes     

1.65μm CH4低温吸收光谱特性研究

在CH₄吸收光谱参数运用于对地球大气以及外星球的遥感探测和模拟上,CH₄光谱参数的准确性十分重要,尤其是在低温情况下的光谱参数。HITRAN数据库中CH₄给出的低温情况下的参数并不完整,同时存在较大的误差.为了对1.65μm的CH₄低温吸收光谱进行测量,采用窄线宽的二极管激光器作为光源,结合自主设计的低温装置,测量了CH₄的低温吸收光谱特性,同时给出6039.70 cm^-1处CH₄的低温吸收光谱作为典型给以阐述,并对吸收谱线自展宽系数的温度依赖系数的测定方法进行了讨论。     

Diode-pumped LiF:F2+* color center lasertunable in 880-995-nm region at room temperature

Pulsed operation of a tunable LiF:F₂^+* color center laser has been obtained at room temperature under pumping by 680-nm fiber-coupled linear array laser diodes for the first time to the authors knowledge. The LiF:F₂^+* tunable laser operates in 880-995-nm region by use of an intracavity birefringent plate. Using a nonselective resonator the laser showed 3% pumping-to-lasing conversion efficiency. In the tunable narrow band operation the measured optical-to-optical conversion efficiency was 2%. The obtained result is expected to cause more widespread applications of diode-pumped LiF:F₂^+* laser and possibly its commercialization