Absorption in the near-ultraviolet wing of the Kr2F*(410 nm) band

An intracavity laser technique has been used to study the absorption of electron-beam pumped Ne/Kr/F2gas mixtures (196 and 300 K) in the "blue wing" of the Kr2F emission continuum. The experiments were conducted at 358 nm using theupsilon' = 0 rightarrow upsilon" = 1transition of the N2(C rightarrow B) laser. Comparing the results with the predictions of a computer model, the species primarily responsible for absorption have been identified as Ne+2, Kr+2, and Kr2F*. The photoabsorption cross sections for Ne+2and Kr2F (Kr+2F-) at 358 nm have been estimated to be8.1 cdot 10^{-19}and5.4 cdot 10^{-18}cm², respectively. The Kr2F* absorption cross section is roughly 20 percent of that reported for Kr+2at the same wavelength. The fluorescence efficiency of Kr2F* ine-beam excited 94.93 percent Ne/5 percent Kr/0.07 percent F2(P_{total} = 4000torr) gas mixtures has been found to be a factor of 2.8 higher than that of the N2(C rightarrow B) band in Ar/5 percent N2mixtures. Also, the rate constant for quenching of Kr2F* by F2was measured to be(4.1 pm 0.5) cdot 10^{-10}cm³. s^-1at 300 K and(3.0 pm 0.5) cdot 10^{-10}cm². s^-1at 196 K.     

Single-mode operation in a 492.4 nm He-Zn II laser using natural zinc

The single-mode operation on the4f^{2}Fdeg_{7/2}-4d^{2}D_{5/2}transition at 492.4 nm in a He-Zn II hollow cathode laser with rectangular pulse discharge is accomplished by using natural zinc experimentally. The method using a laser cavity with an internal mode selector is attempted.     

Multijoule performance of the photolytically pumped XeF(C→A) laser

An XeF(C rightarrow A) laser with output up to 5.8 J/pulse has been demonstrated. The photolytic pumping scheme begins withe-beam excitation of xenon to produce Xe*2fluorescence at 172 nm. This VUV radiation is transmitted through an array of CaF2windows into the laser cell, where it photodissociates XeF2to produce primarily XeF(Bfrac{1}{2}). Collisions with N2buffer gas relax the excited states to XeF(Cfrac{3}{2}), which lases on a transition centered at 481 nm and continuously tunable over more than ±35 nm. Typical values of the experimental parameters were as follows. The 420 kV, 1 me-beam source delivered an average current of 10 A/cm²over an aperture 14 × 100 cm for pulse lengths up to 1 μs. Totale-beam energy available was 3.5 kJ, of which 2.4 kJ was deposited in the xenon. The total VUV energy radiated was 720 J, of which 115 J was coupled into the laser cell. This produced 32 J of available XeF* energy, of which up to 18 percent was extracted as laser energy. The total system efficiency was 0.2 percent. Optimized designs should achieve better than 1 percent efficiency.     

Blue-green atomic photodissociation lasers in group IIb: Zn, Cd, and Hg

Four new laser lines, two in atomic Zn at 481.1 and 472.2 nm and two in atomic Cd at 508.6 and 480.0 nm, are reported. The analog laser lines in Hg at 546.1 and 435.8 nm are studied further. These lines correspond to the transitionsn^{3}S_{1} rightarrow (n-1)^{3}P_{2}andn^{3}S_{1} rightarrow (n-1)^{3}P_{1}of the triplet system of the metals. The medium in the three cases is MI2(M= Zn, Cd, or Hg) vapor at about 1 mbar and the pump is a KrF laser at 248 nm. The blue-green superfluorescent pulse power is in the kilowatt range, with a pulse duration of about 1 ns. The pumping process must involve more than one photon. A sequential three-photon pumping process is proposed for the three cases.     

Spectral characterization of a tunable alexandrite laser by rubidium absorption at 780 nm

Rubidium vapor was used to characterize the output of a tunable, pulsed alexandrite laser operating at 780 nm. Rubidium spectra were obtained at temperatures of 23, 50, 110, and 140°C. Excellent agreement was obtained with computer-synthesized spectra which yielded values for the effective laser bandwidth at different operating conditions. The model assumed a Voigt profile for the rubidium5^{2}P_{3/2} leftarrow 5^{2}S_{1/2}transition and a Gaussian profile for the laser pulse. The model also showed that the laser output was spectrally compact with no evidence of energy outside the narrow 780 nm central feature.     

CMOS Avalanche Photodiode Embedded in a Phase-Shift Laser Rangefinder

This paper presents the design and the characterization of a CMOS avalanche photodiode (APD) working as an optoelectronic mixer. The $hbox{P}^{+}hbox{N}$ photodiode has been implemented in a commercial 0.35-$muhbox{m}$ CMOS technology after optimization with SILVACO. The surface of the active region is $ hbox{3.78} cdot hbox{10}^{-3} hbox{cm}^{2}$. An efficient guard-ring structure has been created using the lateral diffusion of two n-well regions separated by a gap of 1.2 $mu hbox{m}$. When biased at $-$2 V, the best responsitivity $S_{lambda ,{rm APD}} = hbox{0.11} hbox{A/W}$ is obtained at $lambda = hbox{500} hbox{nm}$. This value can easily be improved by using an antireflection coating. At $lambda = hbox{472} hbox{nm}$, the internal gain is about 75 at $-$6 V and 157 at $-$7 V. When biased at $-$6 V, the APD achieves a dark current of 128 $muhbox{A} cdot hbox{mm}^{-2}$ and an excess noise factor $F = hbox{20}$ . Then, the APD is successfully used as an optoelectronic mixer to improve the signal-to-noise ratio of a low-voltage embedded phase-shift laser rangefinder.      

Measurement of the wavelength-dependent photoionization cross section of Se*(1S) in the spectral region of 170-175 nm

The photoionization cross section of excited atomic selenium, Se(¹S0), obtained by photodissociation of OCSe, has been measured in the wavelength region of 170-175 nm using a tunable xenon laser. A minimum value, at 172 nm, was found to be1.2 times 10^{-20}cm², approximately ten times less than a recently calculated value. The photodissociation cross section for OCSe, at the same wavelength, was found to be0.8 times 10^{-16}cm², in good agreement with published work. The effect of an election cooling buffer gas upon the electron production from excited selenium was also investigated.     

Tunable alexandrite lasers

Wavelength tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl2O4:Cr³⁺) over the continuous range from 701 to 818 nm. The tunable emission was observed at room temperature and above in a homogeneously broadened, vibronic, four-level mode of laser action. In this mode the laser gain cross section increases from7 times 10^{-21}cm²at 300K to2 times 10^{-20}cm²at 475K, which results in improved laser performance at elevated temperatures. Efficient 2.5 percent, low-threshold (10 J) operation has been obtained with xenon-flashlamp excitation of the 6 mm diameter × 76 mm length laser rods. Output pulses of greater than 5 J and average power outputs of 35 W have been demonstrated, limited by the available power supply. The emission is strongly polarizedEparallelb, with a gain that is 10 times that in the alternate polarization. The 262 μs, room-temperature fluorescence lifetime permits effective energy storage andQ-switched operation. TunableQ-switched pulses as large as 500 mJ have been obtained with pulsewidths ranging between 33 and 200 ns depending on the laser gain. Laser action has also been demonstrated on the high-gain (3 times 10^{-19}cm²emission cross section)Rline at 680.4 nm and is also polarizedEparallelb. This three-level mode is analogous to the lasing in ruby except that the stimulated emission cross section in alexandrite is ten times larger than for ruby.     

Second-harmonic generation in CDA and CD*A

Efficient second-harmonic generation at 5321 Å has been achieved in CDA and CD*A. At 50-MW pump power, loss-free peak power-conversion efficiency of 57 percent and 45 percent were obtained in CDA and CD*A, respectively, The nonlinear optical constant, corrected for multimode fluctuations, was found to bed_{36}(CDA) = d_{36}(CD*A) = (0.96 pm 0.11) times 10^{-9}ESU, which corresponds tod_{36}(CDA) = d_{36}(CD*A) = 0.92 times d_{36}(KDP). In addition, the temperature variation of the birefringenced(n_{2}^{e} - n_{1}^{o})/dThas been measured to be(8.0 pm 0.2) times 10^{-6}degC^-1for CDA and(7.8 pm 0.2) times 10^{-6}degC^-1for CD*A.     

An experimental study of the diagnostic potential of laser selective excitation spectroscopy for a potassium plasma

A thermally tunedQ-switched ruby laser of moderate power, with emission wavelength at 6939 Å, has been used to selectively excite the4^{2}P_{3/2}-6^{2}S_{1/2}transition in the atoms of a pure potassium plasma of low degree of ionization produced in a hot cathode diode. A pulse of intensified spontaneous emission has been observed at 6939 Å, 6911 Å, and at a number of other wavelengths. The possibility of using this type of interaction for localized plasma diagnostics has been studied experimentally. It has been found that the intensified signal decay time decreases with increasing electron density, thereby providing a potential means for measurement of this parameter. In particular, it is shown that because of a saturation effect, the recorded signal characteristics depend to some extent on the laser parameters. A specially tailored laser performance is suggested as essential in order to overcome these problems and obtain signals which depend unambiguously on the plasma conditions.     

New O II 6640-Å laser line

A prominent red laser line has been observed in oxygen and air at a wavelength of 6640.2 ± 1 Å. This line corresponds to the3p^{2}Smin{1/2}max{0}-3s^{2}P_{1/2}at 6640.90 Å of the O II spectrum. It is the strongest member of the observed emission lines close to the laser line.     

Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2line

Experimental results are shown on the frequency stabilization of a GaAlAs laser using a Doppler-free spectrum in the saturated absorption of the Cs-D2line at 852.1 nm. The frequency stability (Allan variance) between3.0 times 10^{-12}and1.0 times 10^{11}was obtained at the averaging time between 0.1 and 1000 s.     

Blue-Violet Lasing of Optically Pumped GaN-Based Vertical Cavity Surface-Emitting Laser With Dielectric Distributed Bragg Reflectors

Optically pumped GaN-based vertical cavity surface-emitting laser (VCSEL) with two Ta$_{2}$O$_{5}$/SiO$_{2}$ dielectric distributed Bragg reflectors (DBRs) was fabricated via a simplified procedure: direct deposition of the top DBR onto the GaN surface exposed after substrate removal and no use of etching and polishing processes. Blue-violet lasing action was observed at a wavelength of 397.3 nm under optical pumping at room temperature with a threshold pumping energy density of about 71.5 mJ/cm$^{2}$. The laser action was further confirmed by a narrow emission linewidth of 0.13 nm and a degree of polarization of about 65%. The result suggests that practical blue-violet GaN-bsaed VCSEL can be realized by optimizing the laser lift-off technique for substrate removal.      

Two-electron laser transition in Sn(I)?

A new laser oscillation has been observed in a pulsed discharge of He and SnCl4. This oscillation at 1.061 μm corresponds to the5sSp^{3} ^{3}Dmin{1}max{o} rightarrow 5s^{2}5p6p ^{3}P_{2}transition in Sn(I).     

Coherent VUV generation by resonantly-enhanced nonlinear frequency mixing in Cd vapor

Broadly tunable coherent VUV radiation has been generated by two-photon resonant sum-frequency mixing in Cd vapor, using frequency-doubled Nd:YAG laser-pumped dye lasers and the three two-photon resonances5^{1}S_{0} - 5^{1}D_{2}, - 7^{1}S_{0}, and-6^{1}D_{2}. The generated VUV having no spectral structure covers a wavelength range of 119.6-136.8 nm, and the VUV generation efficiency has been measured as a function of wavelength. Besides the tunable VUV, additional intense VUV lines were observed in a spectral range of 145.3-171.1 nm, which were generated by four-wave parametric and second-harmonic processes. The generation mechanisms of these VUV lines are discussed.     

Second-harmonic generation in KB5O8· 4H2O from 217.1 to 315.0 nm

Second-harmonic generation (SHG) has been observed in KB5O8ċ 4H2O (KB5) between 217.1 and 315.0 nm by angle tuning in a single crystal using a single cut. A conversion efficiency of 9.2 percent was observed for type I noncritical phase matching at 217.1 nm for a peak power of 15 kW at 434.2 nm. The nonlinear coefficients d31and d32are estimated to be approximately1.1 times 10^{-10}ESU (4.0 times 10^{-25}m/V) and0.08 times 10^{-10}ESU (0.29 times 10^{-25}m/V), respectively.     

Dispersion of the group velocity refractive index in GaAs double heterostructure lasers

The dispersion of the refractive index corresponding to the group velocityn*_{1}has been measured as a function of wavelength. It is obtained from the longitudinal mode spacing of GaAs buried heterostructure lasers at threshold. The dependence ofn*_{1}on wavelength contains an approximately constant term due to the refractive index n1and a strongly dispersive component due to-lambda (partialn_{1}/ partiallambda). For a given spectral bandwidth, the dispersion ofn*_{1}causes a temporal broadening of a pulse as it passes through the medium. This dispersive effect is shown to contribute to the width of 0.65 ps long pulses obtained recently from mode locked semiconductor lasers. By reducing the length of the laser, the dispersive effect is reduced and it is suggested that pulses as short as 10^-13s should be obtainable from such mode locked semiconductor lasers.     

Tunable Fiber Laser With Ultra-Narrow Linewidth Using A Tunable Phase-Shifted Chirped Fiber Grating

We experimentally demonstrate a tunable $C$ -band erbium-doped fiber ring laser with ultra-narrow linewidth using a tunable phase-shifted linearly chirped fiber Bragg grating (PS-LCFBG) as an intracavity ultra-narrowband filter. The center wavelength of the PS-LCFBG with an ultra-narrow bandwidth of ${≪}$10 pm is thermally tuned by scanning a current-controlled resistance wire along its length. The laser has an ultra-narrow linewidth of ${≪}$1.52 kHz, a tuning range of ${sim}$ 15.5 nm, a good sidemode suppression ratio of ${>}$30 dB, an output power of ${sim}$10 dBm, a small power variation of ${≪}$ 0.2 dB, and a small wavelength variation of ${≪}$0.01 nm. The laser structure is simple and cost-effective.      

Formation kinetics of the triatomic excimer Ar2F*

Detailed fluorescence measurements of electron beam-excited high pressure mixtures of Ar/F2and Ar/NF3have been made in order to investigate the processes leading to the formation of Ar2F*. Three-body collisional quenching of ArF* has been identified as a major formation mechanism. The third-order rate constant for this reaction has been measured to bek_{1} = (1.2 pm 0.2) times 10^{-30}cm⁶. s^-1. In addition quenching rates for collisional de-excitation of Ar2F* by argon and the fluoride donors NF3and F2have been determined. The radiative lifetime has been measured as 219 ± 15 ns. The possible formation of Ar2F* from long-lived excited argon neutrals when using intense excitation densities and low-donor pressures is also briefly discussed.     

The photoionization cross sections of the Rg*2[3Σ+u] excimer states for Ne*2, Ar*2, and Kr*2

Based on the recently determined Rydberg series of the³Sigma+_{u}excimer states of Ne*2, Ar*2and Kr*2, the photoionization cross sections of these molecules are calculated using a single-channel quantum defect method. These cross sections are found to differ considerably from those of the asymptotic metastable atomic Rg*(ns^{3}P_{2}) states, but are in good agreement with recently reported experiments at isolated wavelengths. The implications of these results for VUV and XUV lasers are discussed.