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15 Feb 1983

Volume 42, Issue 4, pp. 309-398

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Continuously tunable coherent spectroscopy for the 0.1–1.0‐THz region

Paul Helminger, James K. Messer, and Frank C. De Lucia

Appl. Phys. Lett. 42, 309 (1983); http://dx.doi.org/10.1063/1.93932 (2 pages) | Cited 43 times

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A spectroscopic system is described that provides coherent, continuously tunable coverage from below 100 GHz to above 1 THz. The phase of the microwave power is directly relatable to WWVB and the spectral purity is such that linewidths of less than 0.01 MHz (HWHM) can be observed without apparent broadening. The flexibility and general applicability of this system make possible a wide variety of submillimeter experiments. In order to illustrate the capabilities of this system we report observations of H2O and CO in the region between 300 and 1100 GHz.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers
42.72.-g Optical sources and standards

Isotopically selective photoionization of mercury atoms

P. Dyer, G. C. Baldwin, C. Kittrell, Dan G. Imre, and E. Abramson

Appl. Phys. Lett. 42, 311 (1983); http://dx.doi.org/10.1063/1.93933 (3 pages) | Cited 10 times

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Isotopically selective resonance ionization of mercury atoms has been accomplished by three‐step excitation via the 6 3P1 and 8 1S0 excited states. Three collinear beams, respectively 254, 286, and 532 nm, from two dye lasers and a pulsed neodymium:yttrium aluminum garnet (ND:YAG) pump laser, were passed through a closed mercury vapor cell containing electrodes to which the ions were drawn by an electric field. The ion current and the 254‐nm fluorescence radiation were measured as a function of laser wavelengths. Hyperfine structures for the 254‐ and 286‐nm transitions were observed.
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32.80.Fb Photoionization of atoms and ions
07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
31.30.Gs Hyperfine interactions and isotope effects
82.20.Tr Kinetic isotope effects including muonium

Reactive outdiffusion of contaminants from (AlGa)As laser facets

P. Tihanyi, D. R. Scifres, and Robert S. Bauer

Appl. Phys. Lett. 42, 313 (1983); http://dx.doi.org/10.1063/1.93934 (3 pages) | Cited 3 times

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We report improved overcoating adhesion and reduction of facet contaminants by predeposition of a 20–50‐Å layer of metallic Al onto cleaved GaAlAs 〈110〉 and GaAs 〈110〉 mirror facets. Electrical, adhesive, and Auger measurements show impurity outdiffusion from the facet into the Al interlayer. This procedure reduces the oxygen by at least a factor of 5 by gettering contaminants from the facet as effectively as ion beam milling, without producing (AlGa)As surface nonstoichiometry inherent in the sputtering process.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Threshold behavior of super‐radiance under continuous pumping

C. T. Lee

Appl. Phys. Lett. 42, 316 (1983); http://dx.doi.org/10.1063/1.93935 (3 pages)

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Recognizing that the super‐radiance emission rate is proportional to the product of the number of cooperative atoms in the upper level and that in the lower level, we propose simple deterministic and stochastic equations to describe the evolution of the super‐radiant atomic system pumped continuously at a constant rate. The steady‐state solutions of these equations display threshold behavior very similar to the laser. This provides yet another example of nonequilibrium phase transition of the second order.
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42.50.-p Quantum optics
05.70.Fh Phase transitions: general studies
05.70.Ln Nonequilibrium and irreversible thermodynamics

Selective enhancement of the 251‐μm line in an optically pumped CH3OH laser

Toshio Sakurai

Appl. Phys. Lett. 42, 319 (1983); http://dx.doi.org/10.1063/1.93936 (3 pages) | Cited 1 time

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To obtain a high output power on the 251‐μm line of a CH3OH laser, four types of far‐infrared output mirror are examined. It is found that the capacitive aluminium‐mesh mirror of the Danielewicz type, which is fabricated by conventional vacuum deposition techniques in the present work, selectively extracts an output power of 18 mW from a 25‐W pump. Also, exact assignment of the line is achieved by tuning the far‐infrared cavity using the mirror.
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42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.62.-b Laser applications
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Switchable coaxial optical coupler using a liquid crystal mixture

V. I. Busurin, M. Green, J. R. Cozens, and K. D. Leaver

Appl. Phys. Lett. 42, 322 (1983); http://dx.doi.org/10.1063/1.93937 (3 pages) | Cited 2 times

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A novel coaxial form of optical coupler has been constructed in which 95% intensity modulation was achieved, using a liquid crystal mixture as the electro‐optic medium. The behavior of this coupler with varying temperature and applied voltage has been elucidated by comparison with the behavior of the same coupler when the liquid crystal was replaced by a silicone oil whose refractive index could be reproducibly and controllably varied.
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42.81.-i Fiber optics
42.79.Gn Optical waveguides and couplers
78.20.Jq Electro-optical effects

Influence of transient absorber gratings on the pulse parameters of passively mode‐locked cw dye ring lasers

D. Kühlke, W. Rudolph, and B. Wilhelmi

Appl. Phys. Lett. 42, 325 (1983); http://dx.doi.org/10.1063/1.93938 (3 pages) | Cited 11 times

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A theoretical explanation of the experimental results obtained by the method of colliding pulse mode locking (CPM) is given. It is shown that, compared to other passive methods, the coherent interaction of the counter‐running pulses in the thin absorber yields considerably shorter pulses with a more favorable stability region. Deviations from an amplifier position being symmetric with respect to the amplification of the counter‐running pulses lead to different energies of the pulses and to a strong decrease of the stability range of the CPM.
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42.55.Mv Dye lasers

Measurement of the linewidth enhancement factor α of semiconductor lasers

Christoph Harder, Kerry Vahala, and Amnon Yariv

Appl. Phys. Lett. 42, 328 (1983); http://dx.doi.org/10.1063/1.93921 (3 pages) | Cited 73 times

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A theory of the amplitude and phase modulation characteristic of a single mode semiconductor laser is presented. In this model the amplitude modulation couples through the complex susceptibility of the gain medium to the phase. We show that this coupling constant can be obtained by a high‐frequency modulation experiment. This measured coupling constant is used to infer the linewidth enhancement factor α as discussed by Henry, and Vahala and Yariv. Experiments confirmed the model and we measured a linewidth enhancement factor ‖α‖=4.6±1.0 for a GaAlAs buried optical guide laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Third‐order optical nonlinearity induced by effective mass gradient in heterostructures

S. Y. Yuen

Appl. Phys. Lett. 42, 331 (1983); http://dx.doi.org/10.1063/1.93922 (3 pages) | Cited 2 times

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In semiconductor heterostructures the electron effective mass can vary spatially, giving rise to a nonlinear force parallel to the mass gradient. In an optical field this nonlinear force modulates the electron mass through its position dependence, leading to a novel third order optical nonlinearity. The susceptibility of this process is calculated through the kinetic equations for the electrons. It is found that large nonlinear refractive indices can be obtained with subpicosecond relaxation times. Possible device configurations are discussed.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.62.-b Laser applications

Optical bistability in InSb at room temperature with two‐photon excitation

A. K. Kar, J. G. H. Mathew, S. D. Smith, B. Davis, and W. Prettl

Appl. Phys. Lett. 42, 334 (1983); http://dx.doi.org/10.1063/1.93923 (3 pages) | Cited 25 times

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We report the observation of optical bistability in an InSb resonator at room temperature. This effect and fringe shifts were caused by nonlinear refraction induced by two‐photon absorption of radiation from a single longitudinal mode injection‐locked pulsed CO2 laser operating at 9.6–10.6 μm. Intensities as low as 100 kW/cm2 were found to be sufficient to tune the 250‐μm‐thick cavity through a fringe maximum. From our results we deduce a value of χ(3) of the order of 10−4 esu over the range of intensities investigated.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
85.60.-q Optoelectronic devices
42.60.Fc Modulation, tuning, and mode locking

Optically pumped ring laser oscillation to vibrational levels near dissociation and to the continuum in Na2

John T. Bahns, K. K. Verma, A. R. Rajaei‐Rizi, and W. C. Stwalley

Appl. Phys. Lett. 42, 336 (1983); http://dx.doi.org/10.1063/1.93924 (3 pages) | Cited 12 times

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Unidirectional laser oscillation of Na2 dimers has been observed using 5682‐Å single‐mode Kr+ laser pumping. This laser action involves not only bound‐bound transitions, but also (for the first time) bound‐free transitions between two strongly bound electronic states (the A 1Σ+u and X 1Σ+g states). Twelve bound‐bound transitions and two regions of bound‐free emission, in the region 7200–8300 Å, were observed. Previously reported laser‐induced fluorescence results were used to assign both the bound‐bound and bound‐free transitions to the A 1Σ+u –X 1Σ+g band system of Na2. The bound‐bound transitions are also of particular interest because they all occur to very highly excited vibrational levels within 10% of dissociation (laser oscillation to lower levels should also be possible but was not examined). The pressure for optimum intensity was found to be ∼0.65 Torr.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers

Optically integrated coherently coupled AlxGa1−xAs lasers

B. F. Levine, R. A. Logan, W. T. Tsang, C. G. Bethea, and F. R. Merritt

Appl. Phys. Lett. 42, 339 (1983); http://dx.doi.org/10.1063/1.93925 (3 pages) | Cited 3 times

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We have succeeded for the first time in integrating on the same chip, two electrically independent lasers which are coherently coupled via the overlap of their lateral optical fields. Such coupled lasers show excellent single longitudinal mode characteristics which are considerably improved over that of the individual lasers. They are therefore promising devices for high data rate optical communication systems.
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42.55.Px Semiconductor lasers; laser diodes
42.55.-f Lasers
42.60.By Design of specific laser systems
42.50.-p Quantum optics

Measurement of picosecond ultraviolet laser pulsewidths using an electrical autocorrelator

J. Bokor, P. H. Bucksbaum, and D. H. Auston

Appl. Phys. Lett. 42, 342 (1983); http://dx.doi.org/10.1063/1.93926 (3 pages) | Cited 2 times

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The use of an electrical autocorrelator constructed of two ultrafast photoconducting detectors as a general technique for the measurement of picosecond ultraviolet laser pulsewidths is demonstrated.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
06.60.Jn High-speed techniques (microsecond to femtosecond)
06.30.Ft Time and frequency

Long wavelength Pb1−xSnxTe homostructure diode lasers having a gallium‐doped cladding layer

A. Zussman, Z. Feit, D. Eger, and A. Shahar

Appl. Phys. Lett. 42, 344 (1983); http://dx.doi.org/10.1063/1.93927 (3 pages) | Cited 3 times

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The electron concentration in Ga‐doped liquid phase epitaxy (LPE) layers of Pb1−xSnxTe was studied as a function of the Ga concentration in the growth solution for various x compositions. Maximum electron concentrations of 5×1019 cm−3 and 2×1018 cm−3 were measured for x=0 and x=0.3, respectively—the highest values ever published for these LPE grown compositions. n+‐p‐p+ Pb1−xSnxTe homostructure diode lasers with a Ga‐doped cladding layer were fabricated. The lasers showed extended wavelength ranges (11.5≤λ≤18.5 μm for x=0.24 and 8.2 μm≤λ≤11.2 μm for x=0.12), and low threshold current densities (30 A/cm at T=10 K). The threshold current density at low temperatures was found to be determined by excess tunneling currents.
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42.55.Px Semiconductor lasers; laser diodes
68.55.-a Thin film structure and morphology
72.20.My Galvanomagnetic and other magnetotransport effects

cw recombination laser action in a cadmium vapor arc

W. T. Silfvast, O. R. Wood, and J. J. Macklin

Appl. Phys. Lett. 42, 347 (1983); http://dx.doi.org/10.1063/1.93928 (3 pages) | Cited 6 times

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Continuous‐wave laser oscillation at 1.40, 1.43, 1.45, and 1.64 μm has been achieved in a recombining plasma produced by a Cd vapor arc in the presence of low‐pressure rapidly flowing He gas. The variation of gain with distance from the arc, calculated using a simple recombination model, is in close agreement with experiment. The experimental techniques used in this work should be applicable to the development of cw lasers in other metal vapor arcs.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Wave propagation in a finely laminated periodic elastoacoustic medium

Michael Schoenberg

Appl. Phys. Lett. 42, 350 (1983); http://dx.doi.org/10.1063/1.93929 (3 pages) | Cited 9 times

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The exact solution for plane wave propagation through periodically alternating solid and fluid layers has been derived for all frequencies and all wave numbers. In the low‐frequency limit an explicit dispersion relation is found relating the wave slowness parallel to the layering to that perpendicular to the layering. At any angle of propagation, except perpendicular, there are two waves: a fast wave and a slow wave. The tangential motion across a solid fluid interface for the fast wave is in phase, and for the slow wave, out of phase. An equivalent medium is found which has the same equation of motion with an anisotropic density tensor as a periodically layered fluid, but which has a constitutive relation relating pressure and dilation which is nonlocal in space and time. This equivalent medium exhibits the same wave propagation properties as the layered solid, fluid medium in the long wavelength limit and is called an elastoacoustic medium.
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43.20.Bi Mathematical theory of wave propagation
43.20.Hq Velocity and attenuation of acoustic waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
83.10.Ff Continuum mechanics

c‐axis inclined ZnO piezoelectric shear wave films

J. S. Wang and K. M. Lakin

Appl. Phys. Lett. 42, 352 (1983); http://dx.doi.org/10.1063/1.93930 (3 pages) | Cited 22 times

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This letter reports on the growth and characterization of ZnO films having c axis oriented 40° to the substrate normal. These films are of significant interest for shear wave generation for bulk wave delay lines and resonators. The films were grown on Si wafers or membranes under low pressure and high growth rate conditions in a reactive dc planar magnetron sputtering system having an auxiliary anode structure. Shear wave resonators were fabricated and used for film evaluation. A ZnO/Si composite resonator exhibited a Q of approximately 4600 at 293‐MHz fundamental resonance. The effective coupling coefficient of the film alone was found to be 17% (k2=0.029) using an edge‐only supported ZnO plate resonator. The temperature coefficient of the ZnO resonator was found to be −36 ppm/°C and −20.5 ppm/°C for the composite structure.
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81.15.Cd Deposition by sputtering
77.65.-j Piezoelectricity and electromechanical effects
62.65.+k Acoustical properties of solids
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Plasma rotation measurements using spectral lines from charge‐transfer reactions

R. C. Isler and L. E. Murray

Appl. Phys. Lett. 42, 355 (1983); http://dx.doi.org/10.1063/1.93931 (3 pages) | Cited 53 times

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The central toroidal rotation velocities of tokamak plasmas have been measured from the Doppler shifts of spectral lines that are excited by charge transfer of the neutral hydrogen heating beams with fully ionized oxygen.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.55.Fa Tokamaks, spherical tokamaks
52.55.Hc Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices
52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Origin of lamellae in radiatively melted silicon films

W. G. Hawkins and D. K. Biegelsen

Appl. Phys. Lett. 42, 358 (1983); http://dx.doi.org/10.1063/1.93939 (3 pages) | Cited 52 times

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Coexisting liquid and solid regions have been reported to occur in the melt zone of radiatively heated silicon thin films. We demonstrate here the mechanism of creation of these lamellae. The existence and characteristic size of the lamellae are shown to arise simply from the increased reflectivity of silicon on melting and the thermal properties of the sample.
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81.10.Fq Growth from melts; zone melting and refining
68.55.-a Thin film structure and morphology

Oxidation of silicide thin films: TiSi2

F. d’Heurle, E. A. Irene, and C. Y. Ting

Appl. Phys. Lett. 42, 361 (1983); http://dx.doi.org/10.1063/1.93940 (3 pages) | Cited 41 times

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The oxidation of TiSi2 thin films on polysilicon illustrates extreme examples of behavior. At 700 °C in wet O2, one observes the formation of titanium oxide and the simultaneous rejection of silicon towards greater depths, away from the oxidized surface layer. At 1100 °C with the same type of sample, one observes the growth of a metal‐free layer of SiO2, the formation of which required not only the use of the whole available polysilicon, but the reduction of the initial disilicide to a lower silicide, mostly TiSi. These observations are discussed in terms of previous results obtained either with TiSi2 or with other silicides, and in terms of what is known about the thermodynamics of the system titanium oxide‐silicon oxide.
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68.55.-a Thin film structure and morphology
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.40.Bj Oscillations, chaos, and bifurcations

Quantum transport in a single layered structure for impurity scattering

Johnson Lee, Harold N. Spector, and Vijay K. Arora

Appl. Phys. Lett. 42, 363 (1983); http://dx.doi.org/10.1063/1.93941 (3 pages) | Cited 15 times

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In this letter we present results for the mobility of electrons confined in a layered structure when the scattering of the confined carriers is dominated by ionized impurity scattering. In the size quantum limit, the mobility is found to decrease with the layer thickness in contrast to the situation where acoustic phonon scattering is dominant. In the latter case, the mobility is found to increase with the layer thickness. We have considered the effects of both background and remote impurities on the mobility of the confined carriers. The results which we have obtained are considerably different from those currently available in the literature.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.80.Ey III-V and II-VI semiconductors

Stereoscopic depth analysis by thermal wave transmission for nondestructive evaluation

G. Busse and K. F. Renk

Appl. Phys. Lett. 42, 366 (1983); http://dx.doi.org/10.1063/1.93942 (3 pages) | Cited 21 times

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Thermal wave transmission probing is used for nondestructive remote subsurface flaw detection in metal. It is shown that depth information of subsurface structure is obtained when two thermal wave sources are operated simultaneously in a stereoscopic arrangement.
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05.70.Ce Thermodynamic functions and equations of state
81.70.-q Methods of materials testing and analysis

Efficient visible photoluminescence in the binary a‐Si:Hx alloy system

D. J. Wolford, J. A. Reimer, and B. A. Scott

Appl. Phys. Lett. 42, 369 (1983); http://dx.doi.org/10.1063/1.93920 (3 pages) | Cited 61 times

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We report the photoluminescence (PL) and structural properties of a new class of efficient visible‐light‐emitting semiconductors: low defect density a‐Si:Hx alloys. For films prepared by the (thermal) homogeneous chemical vapor deposition (HOMOCVD) method, new broadband PL develops for x>0.3, reaching a peak emission energy of 2.05 eV for a hydrogen content x=0.66 (40 at. % H). We attribute the wide gaps to the influence of Si–H bonding on the density of states near the valence band edge. We ascribe the new PL process to band‐to‐band recombination from within the alloy band tails. This emission persists at room temperature with an integrated intensity comparable to conventional light‐emitting diode (LED) materials. Qualitatively similar results are obtained for low‐temperature‐deposited rf plasma films prepared from Si2H6, but not from SiH4. We show that a low Si dangling bond concentration is the key factor, for all the different film types, to achieving efficient luminescence.
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78.40.Fy Semiconductors

Absence of the Gunn effect in p‐In0.53Ga0.47As

E. Otsuka

Appl. Phys. Lett. 42, 372 (1983); http://dx.doi.org/10.1063/1.93943 (2 pages)

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The reported absence of the Gunn effect in photoexcited p‐In0.53Ga0.47As is discussed from the viewpoint of the lesser electron scattering rate by acceptors than by donors. The donor‐to‐acceptor ratio of electron scattering cross sections is calculated for the carrier density range 1015–1020 cm−3. It is found that the electron‐acceptor scattering cross section is by two orders of magnitude smaller than the electron‐donor scattering cross section.
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72.20.Dp General theory, scattering mechanisms
72.80.Ey III-V and II-VI semiconductors
72.10.-d Theory of electronic transport; scattering mechanisms

Evidence of stress‐mediated Hg migration in Hg1−xCdxTe

P. M. Raccah, U. Lee, J. A. Silberman, W. E. Spicer, and J. A. Wilson

Appl. Phys. Lett. 42, 374 (1983); http://dx.doi.org/10.1063/1.93944 (3 pages) | Cited 15 times

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Photoemission results from some 〈110〉 cleaved surfaces of Hg1−xCdxTe indicate that the Fermi level is pinned suggesting that while the bulk of the material is p type the area stressed during cleavage has been converted to n type. Electrolyte electroreflectance (EER) measurement confirmed the n‐type character of the cleaved surface and showed that the alloy composition x at the surface, after cleavage, is high (x=0.22) compared to the bulk value (x=0.185). The high x value associated with the n character indicates that under stress the Hg migrates, at least partially, via the formation of donor defects. The defect density is reflected in the EER linewidth.
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78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
81.65.-b Surface treatments
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