Showing papers on "Tunable laser published in 1979"

Calculated spontaneous emission factor for double-heterostructure injection lasers with gain-induced waveguiding

Abstract: The fraction of spontaneous emission going into an oscillating laser mode has been calculated. It is shown that this fraction strongly depends on the strength of astigmatism in the laser output beam. Therefore the spontaneous emission factor in planar stripe lasers with narrow stripe is in the order of 10-4and by one order of magnitude larger than in injection lasers with a comparable active layer volume and with a built-in index waveguide. It is shown that the spontaneous emission factor is approximately proportional to the solid angle of laser radiation and nearly independent of the transverse active layer dimensions. Owing to the large spontaneous emission factor, the spectral width of narrow planar stripe lasers is significantly broader compared to narrow stripe lasers with a built-in index waveguide. In addition the large spontaneous emission coefficient also yields a much stronger damping of relaxation oscillations.

Recent advances in lead-chalcogenide diode lasers

Abstract: The fundamental material properties of Pb1−xSnxTe, PbS1−xSex and Pb1−xSnxSe are reviewed. Expressions for the temperature and compositional dependences of the band parameters and dielectric constants based on recently published data are presented. As far as device technology is concerned, crystal growth techniques and diode fabrication procedures which are in use today are reviewed and compared. A comprehensive summary of laser properties like threshold current density, output power, efficiency, maximum operating temperature and tuning range of different diode structures are presented. Application related aspects such as long term stability are treated. Recent progress in laser theory is applied to explain experimentali th vs.T curves. The various laser applications are reviewed briefly. A new technique for monitoring gas concentrations using pulsed lasers and an integral method for signal processing is discussed and compared with the differential absorption, derivative spectroscopy. A long-path trace-gas monitoring system incorporating this new technique is presented.

Optically pumped CW dimer lasers

Abstract: Bound-bound electronic transitions in simple molecules are generally suited to realize efficient multiline laser oscillation in the visible and ultraviolet spectral region. By means of optical excitation with argon and krypton lasers, CW laser oscillation could be obtained for various homonuclear diatomic (dimer) molecules such as Li 2 , Na 2 , K 2 , Bi 2 , S 2 , Te 2 , and I 2 , with emission of several hundred laser lines in the spectral range of about 400-1350 nm. The principles of these lasers and the general dependence of threshold and output power on temperature, pressure, length of vapor zone, and some other parameters is discussed. To achieve satisfactory CW operation, low quenching losses for the upper laser level population and a sufficiently fast relaxation of the population of the lower laser level are necessary. Under optimum operation conditions, efficiencies up to 15 percent, multiline output powers up to 400 mW, and single line-single frequency output powers up to 200 mW were achieved. These dimer lasers are three-level laser systems. In case of coherent optical excitation, two-photon or Raman-type processes contribute to the amplification process. Due to these mechanisms the forward direction is strongly favored and in a ring laser system spontaneous unidirectional oscillation is obtained. By means of a suitable three-level model, analytical and numerical calculations of gain profiles are performed and compared with experiments. These optically pumped molecular lasers are suited for various spectroscopic and kinetic investigations, for frequency standards or as simple and efficient systems to convert pump laser radiation into other spectral regions.

Experimental and analytic studies of coupled multiple stripe diode lasers

Abstract: Experimental and analytic studies of coupled multiple stripe (CMS) phase-locked, room-temperature diode lasers are reported. Such devices generate high-power well-collimated beams, which potentially may be electronically scanned in the manner of phased array radar. For the tested devices with ten conducting 3 μm stripe contacts on centers separated by D and coupled by curved waveguide sections, data from four stripe geometries with D ranging from 10 μm to 27.4 μm are compared and overall optimal characteristics occur for D = 10 \mu m. In that case, threshold current densities are comparable to solid area lasers, differential quantum efficiency is approximately 60 percent, and maximum observed pulsed power per facet is on the order of 1 W.

A possible model for sustained oscillations (pulsations) in (Al,Ga)As double-heterostructure lasers

Abstract: A model explaining the origins of sustained oscillations in (Al,Ga)As double-heterostructure lasers is proposed and plausibility arguments of its applicability are given. The model relies on saturable-absorber Q -switching to produce the pulsations, with the saturable absorption located near the ends of the laser in regions where surface recombination reduces the injected-carrier density. The sides of the active volume, or defects which cause carrier recombination within the active volume, may also cause such pulsations according to this model.

Lateral transverse mode instability and its stabilization in stripe geometry injection lasers

Abstract: A numerical analysis has been carried out on the behavior of semiconductor injection lasers with a stripe geometry double-heterostructure, taking into account spatial hole-burning and its effect on the waveguiding. It is shown that spatial hole-burning, the negative dependence of refractive index eta on the excited carrier density n (d_{eta}/ dn , and the lack of complete symmetry in any real laser structure are the three critical factors responsible for the lateral mode instability leading to such anomalous behaviors these lasers exhibit as a "kink" in the light output versus current relation and the lateral shift in the emission spot. Effects of rigid refractive index and gain-loss profiles built into the laser crystal on the mode stability have been examined, and conditions for kink-free, single lateral mode oscillations have been investigated.

Tunable-laser performance in BeAl 2 O 4 :Cr 3+

Abstract: Broadly tunable laser operation has been obtained at room temperature from the vibronic bands of single-crystal BeAl(2)O(4):Cr(3+) under Xe-flashlamp excitation. Continuous tuning is obtained from 701 to 794 nm, with maximum power at 750 nm. Long-pulse operation employing 6.3-mm x 76-mm rods easily provides 500 mJ in 200-microsec bursts, whereas 70-mJ, 120-nsec pulses are obtained under Q-switch operation.

A condition of single longitudinal mode operation in injection lasers with index-guiding structure

Abstract: A condition for single longitudinal mode operation (SMO, for short) of index-guided injection lasers is given theoretically and supported by experiment. For SMO, the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide. Inclusion of the spontaneous emission into the lasing field must be reduced by using a thinner active region. In terms of the impurity concentration of the active region, the undoped case is the most stable for temperature variation. A heavily doped active region may also produce SMO. The thermal resistance must be reduced to increase temperature stability. MO with a fixed lasing wavelength is experimentally obtained by temperature control up to an injection current of twice threshold.

New lines in the UV: SRS of excimer laser wavelengths

Abstract: The UV excimer lasers ArF, KrCl, KrF, and XeCl were utilized to create new families of UV lines by multiple orders of broad-band nonresonant stimulated Raman scattering (SRS) in the media H 2 , D 2 , CH 4 , and LN 2 . Mixed-media and excited-state SRS were also studied.

Free-electron lasers

Abstract: • ultra-sensitive lidar and remote sensing • high-resolution excited state spectroscopy • generation of tunable, high brightness singlemode radiation by optical phase-locking techniques • Doppler-free nonlinear spectroscopy and Doppler limited absorption spectroscopy • compact x-ray sources • studies of the non-classical nature of FEL light • optical pulse compression and pulse shaping • photo-chemistry and surface science • novel FEL configurations including multiple inverse-tapered undulators The undulator section of the MOPA III FEL

Free‐electron lasers using the Smith‐Purcell effect

Abstract: The theory of linear and stimulated free‐electron lasers using the Smith‐Purcell effect is presented. These lasers depend upon the resonant interaction of an electron beam with the longitudinal field of a surface‐harmonic wave on a diffraction grating. Detailed design criteria for the linear Smith‐Purcell‐effect laser are determined. Numerical estimates show that infrared lasers are feasible at beam currents smaller than 1 A and that single‐mode operation may be achieved. Saturation estimates determine the power output in the range 102 W. An expression for the gain of the stimulated Smith‐Purcell laser is derived. The frequency up‐conversion factor for the stimulated interaction may be very large. Its possible use as a soft x‐ray laser is limited by the available intensity of the pump wave.

A simplified theory of the optogalvanic effect

Abstract: We present a simple phenomenological theory of the optogalvanic effect based on the multiplication of an electron within the plasma. The dependence of the signal on current and pressure and its temporal behavior are predicted for atoms irradiated by chopped CW lasers and pulsed lasers. Experimental data obtained by pulsed lasers are presented and interpreted.

Broadly tunable cw operation of Ni : MgF2 and Co : MgF2 lasers

Abstract: Operation of cw Ni : MgF2 and Co : MgF2 lasers with an external cavity has produced broadly tunable emission in the near infrared. The Ni : MgF2 laser was tuned continuously from 1.61 to 1.74 μm and the Co : MgF2 laser from 1.63 to 2.08 μm. Optical pumping with a 1.32‐μm Nd : YAG laser and conduction cooling of the laser crystals to 80 K yielded stable spiking‐free TEM00 outputs from both lasers with maximum cw output powers of about 100 mW. The Ni : MgF2 laser was operated with a single‐frequency output of 20 mW and was Q switched to generate a peak power output of 140 W at a 100‐Hz repetition rate.

Picosecond optical pulse generation from an r.f. modulated AlGaAs d.h. diode laser

Abstract: AlGaAs d.h. lasers with relatively low d.c. bias were demonstrated to be quite feasible for generation of a train of 30 ps optical pulses at a modulated frequency of below the GHz range. The pulse envelope width was measured by an s.h.g. correlation method as well as an ultrafast streak camera; the results agreed fairly well.

Heterodyne frequency measurements with a tunable diode laser-CO(2) laser spectrometer: spectroscopic reference requencies in the 9.5-microm band of carbonyl sulfide.

Abstract: The frequencies of twelve carbonyl sulfide absorption lines near 9.5 microm have been measured by means of a heterodyne frequency measuring technique, which uses a frequency stabilized CO(2) laser and a tunable diode aser. The diode laser was locked to the peak of each OCS absorption line by means of a first derivative frequency lock procedure. In addition to lines in the 02(0)0-00(0)0 band, measurements also include some nearby OCS hot band features as well as lines in isotopically enriched samples of OC(34)S, O(13)CS, and (18)OCS. These measurements are part of an effort to provide frequency standards for the calibration of tunable IR laser devices.

An AlGaAs window structure laser

Abstract: Extremely high optical power density emission was achieved with an AlGaAs "window structure" laser in CW operation as well as pulsed operation by increasing the threshold of the catastrophic optical damage (COD) on mirrors. A Zn diffused "window stripe" laser consists of the Zn diffused p-type light emitting region with low effective energy gap in the central part and the n-type window regions with high effective energy gap at both ends of the cavity. The maximum available optical power in pulsed operation was at least one order of magnitude higher than the COD threshold in conventional structures. 80 mW optical power in CW operation was achieved in the Zn diffused window stripe laser with a 5 μm wide stripe. Furthermore, gradual degradation due to the photoenhanced mirror oxidation has been reduced significantly under long term CW operation.

Lateral mode behavior in narrow stripe lasers

Abstract: A theoretical and experimental description of the lateral mode behavior in oxide-insulated stripe geometry lasers with stripe width below 8 μm is given. The analysis is based on the waveguiding effects of carriers injected into the active region, and includes accurate, self-consistent solutions to the waveguide and carrier distribution equations. In agreement with experiment, wide ( \geq12 \mu m) near-field patterns and non-Gaussian far-field patterns are found for the fundamental mode. As the current is increased above threshold, the near fields become progressively wider and the far fields develop a twin peak structure. The optical properties of the output are dominated by a one-dimensional analog of spherical aberration. It is shown that high pulsed output power may be obtained in fundamental lateral mode without incurring catastrophic facet damage.

Photoacoustic Raman spectroscopy (PARS) using cw laser sources

Abstract: We have devised a new nonlinear spectroscopic technique, photoacoustic Raman spectroscopy (PARS), which uses acoustic methods to detect energy deposited in a molecular gas by the process of stimulated Raman scattering. The technique was demonstrated by stimulated Raman excitation of the 2916.7‐cm−1 ν1 symmetric stretch vibrational mode of CH4 using two cw laser sources (an argon ion laser at 514.5 nm and a tunable dye laser near 605.4 nm). Excellent agreement between calculated and experimentally observed PARS signals was obtained for CH4.

Visible absorption by electron-beam pumped rare gases

Abstract: The temporal and spectral behavior of absorption in the visible by e -beam excited argon, krypton, and xenon have been investigated with and without additives. The probe light used was from an argon-ion pumped, tunable dye laser, or from the visible lines of the argon-ion laser itself. Strong absorption was observed at all wavelengths investigated (450-620 nm). Structured absorptions out of atomic and molecular excited states have been identified by their temporal, spectral, and pressure behavior. The ubiquity of these absorptions, which is not fully understood, should have serious implications for the development of new visible lasers that operate during the electron-beam pumping pulse.

GaAs-Al x Ga 1-x As strip buried heterostructure lasers

Abstract: A new laser structure, the strip buried heterostructure (SBH) laser, using an active strip on a low-loss waveguide is described, theoretically analyzed, and experimentally characterized under both pulsed and CW operations. The waveguiding properties and laser threshold conditions are analyzed using the effective refractive index approximation. The calculated results agree fairly well with measured results. Pulsed output powers as high as 400, 230, and 130 mW/mirror without AR coating have been obtained at "catastrophic" mirror failure for SBH lasers with 10, 5, and 3 μm strips, respectively. Throughout this entire current injection range, stable transverse mode operation and excellent linearity and symmetry in light-current characteristic from each mirror were obtained. Intermodulation products were measured for 5 μm strip SBH lasers. At an average power of 4 mW and modulation depth of 80 percent, the third-order component was about 48 dB below the fundamental. Excess noise above threshold was not present. For SBH lasers with efficient injection current confinement and active strip area of 380 \times 10 \mu m, pulsed and CW current thresholds were about 74 and 85 mA, respectively. The average external quantum efficiency was about 45 percent. CW operation has been achieved at a heat-sink temperature as high as 115°C. The current threshold has an exponential variation with temperature exp ( T/T_{0} ) where T_{0} = 110 K. For SBH lasers with strip widths \sim5 \mu m, stable fundamental mode oscillation in both transverse directions was observed up to 9 times threshold. Far-field beam divergences of 8-10\deg and 26-30\deg were obtained in directions parallel and perpendicular to the junction plane, respectively. Single-longitudinal-mode operation up to twice threshold was obtained for SBH lasers with strip widths \lsim5 \mu m under both pulsed and CW operations. Relaxation oscillation and self-pulsation were not observed for SBH lasers with clean transverse modes in pulsed response up to current injection levels as high as 4 \times I_{th} . For these particularly good diodes, self-pulsation was not observed before aging under CW operation in preliminary experiments. Aging studies have not yet been performed. Densely packed monolithic linear arrays of SBH lasers with center-to-center spacing of 15 μm were also studied. They exhibited similar laser characteristics as in single SBH lasers, but with increased maximum pulsed output power/mirror, approximately ( 310 \times N ) and ( 150 \times N ) mW for arrays with ∼10 and \sim4 \mu m strips, respectively. N is the number of lasers in the array. Spectral behavior of these arrays was also studied as a function of injection current and temperature.

Single-mode c.w. ridge-waveguide laser emitting at 1.55 μm

Abstract: Single-mode c.w. operation at =1.55 μm has been achieved in ridge-wavelength lasers fabricated using InGaAsP quaternary alloys. These lasers are promising candidates for future long-distance optical communications systems.

Continuous-wave laser action of (F 2 + ) A centers in sodium-doped KCl crystals

Abstract: Broadly tunable laser action is reported for the (F2+)A center in sodium-doped, additively colored KCl. The laser is continuously tunable from about 1.62 to 1.91 μm, has a continuous-wave threshold of under 10-mW absorbed power, and can be stored for at least limited periods at room temperature without losing its lasing capability.

Infrared double resonance of SF6 with a tunable diode laser

Abstract: Double resonance spectroscopy has been carried out on the ν3 band of SF6 using a CO2 laser pump and a tunable diode laser probe. Power broadening of the pumped transition is observed, and a value for the transition moment μ12?0.3×10−18 esu cm is obtained. Off‐resonant pumping of all symmetry components in the J manifold coupled to the pump laser is observed; this is attributed to field‐induced mixing of nearly degenerate fine‐structure levels in the vibrational ground state of the molecule. From the decay of the double resonance signals, we measure relaxation times Pτ= (24±3) nsec Torr for 2‐level signals and Pτ = (43±11) nsec Torr for 3‐level signals, corresponding to an effective cross section of 170 A2. Excited‐state transitions corresponding to 2ν3←ν3 with J=32 are observed. The implications for multiple infrared photon excitation models are considered.

Tunable diode laser spectroscopy in the infrared: some practical considerations of techniques and calibration with ν 2 lines of HCN

Abstract: A tunable diode laser has been incorporated as a source in an operating high resolution vacuum grating spectrometer. The advantages of such a system for recording molecular spectra have been elaborated. In the process of developing this system, several practical problems came about, and it has been considered useful to document the manner in which they have been resolved. In particular, for work in the region of 15 μm, it was advantageous to develop an air-spaced Fabry-Perot etalon to record fringes simultaneously with the scanning of molecular spectra. This was successfully done, and the ν2 band lines of the HCN molecule at 14 μm have proved to be ideally suited for determining the fringe spacing spectroscopically.

Diode laser-CO2 laser heterodyne spectrometer - Measurement of 2sQ/1,1/ in 2 nu 2-nu 2 of NH3

Abstract: A carbon dioxide laser has been coupled with a tunable diode laser spectrometer for heterodyne calibration of molecular spectra. The output of the diode laser is measured to be 10–15 MHz wide and is stable to within ±2 MHz. The frequency of the 2sQ(1,1) transition in the 2ν2 − ν2 band of ammonia is measured to be 949.44746(24) cm−1.

Laser-pumped molecular lasers - Part II: Submillimeter laser experiments

Abstract: We report the first experimental determination of the gain spectrum of a laser-pumped submillimeter laser amplifier. Single-mode pump and submillimeter oscillators were used to determine the gain as a function of submillimeter laser frequency, pump intensity, relative polarization, and molecular gas pressure. The 385 μm transition in D 2 O and the 496 μm transition in CH 3 F, both pumped by a CO 2 laser, were investigated. The use of single-mode lasers allows a direct comparison with theory. Good agreement is obtained with our recent theory which takes into account two photon contributions to the gain as well as space orientation ( M -level) molecular degeneracy.