Showing papers in "Applied Physics Letters in 1971"
TL;DR: In this paper, a new electrooptical effect in twisted nematic liquid crystals is described which allows variation of the rotation of linearly polarized light continuously from 0° to 90°.
Abstract: A new electro‐optical effect in twisted nematic liquid crystals is described which allows variation of the rotation of linearly polarized light continuously from 0° to 90°. It requires lower voltages than other electro‐optic effects.
1,090 citations
TL;DR: In this paper, the authors investigated laser oscillation in periodic structures in which feedback is provided by backward Bragg scattering, and showed that the feedback mechanism is distributed throughout and integrated with the gain medium.
Abstract: We have investigated laser oscillation in periodic structures in which feedback is provided by backward Bragg scattering These new laser devices are very compact and stable as the feedback mechanism is distributed throughout and integrated with the gain medium Intrinsic to these structures is also a gratinglike spectral filtering action We discuss periodic variations of the refractive index and of the gain and give the expression for threshold and bandwidth Experimentally we have induced index periodicities in gelatin films into which rhodamine 6G was dissolved The observed characteristics of laser action in these devices near 063 μm are reported
859 citations
TL;DR: In this article, a single vertically directed focused TEM00-mode cw laser beam of ∼250 mW is sufficient to support stably a ∼20μ glass sphere.
Abstract: The stable levitation of small transparent glass spheres by the forces of radiation pressure has been demonstrated experimentally in air and vacuum down to pressures ∼1 Torr. A single vertically directed focused TEM00‐mode cw laser beam of ∼250 mW is sufficient to support stably a ∼20‐μ glass sphere. The restoring forces acting on a particle trapped in an optical potential well were probed optically by a second laser beam. At low pressures, effects arising from residual radiometric forces were seen. Possible applications are mentioned.
780 citations
TL;DR: In this article, the refractive indices of ZnGeP2, point group 42m, have been determined from 0.64 to 12 μ and the nonlinear optical coefficient d14 for second harmonic generation (SHG) measured relative to d14 of GaAs is 0.83 ± 15%.
Abstract: The refractive indices of ZnGeP2, point group 42m, have been determined from 0.64 to 12 μ. ZnGeP2 has positive birefringence with reasonable temperature tunability and a band gap in the visible. Its nonlinear optical coefficient d14 for second harmonic generation (SHG) measured relative to d14 of GaAs is 0.83 ± 15%. The birefringence of ZnGeP2 is not large enough to allow phase‐matched SHG, but nondegenerate phase‐matched three‐frequency mixing is possible and the parametric oscillator threshold power is calculated for several situations. A redetermination of the coefficient d31 in CdSe is made and the materials compared. It is concluded that ZnGeP2 may be a most promising material for parametric generation in the 0.8– to 12‐μ region.
574 citations
TL;DR: In this article, a pyroelectric coefficient (dP/dT = 2.4 ± 0.7 nC/cm2°C) comparable to that of single-crystal LiNbO3 is observed.
Abstract: Oriented films of polyvinylidene fluoride [(CH2CF2)n], a polar polymer possessing symmetry mm2, can be made significantly pyroelectric and optically nonlinear by poling in an electric field. A pyroelectric coefficient (dP/dT = 2.4 ± 0.7 nC/cm2°C) comparable to that of single‐crystal LiNbO3 is observed. The nonlinear optical coefficients d33, d32, and d31 of polyvinylidene fluoride (PVF2) are measured relative to d11 of crystalline quartz [d33 (PVF2)≃2d31 (PVF2) ≃d11(SiO2); d32(PVF2)≃0]. The poled films have specific advantages for pyroelectric detection of electromagnetic radiation and for optical parametric devices.
409 citations
TL;DR: In this paper, a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials was proposed. But it was only applied to CdS crystals at 2°K and showed that net gains as high as 160 cm−1 at λ = 4907 A are possible with ∼ 12MW/cm2 optical pump power density from a nitrogen laser.
Abstract: We report a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials. Amplified spontaneous emission is used to determine the gain factor by relating the measured variation in light output to variation in the length of the excitation beam. Results for CdS crystals at 2°K are presented that indicate net gains as high as 160 cm−1 at λ = 4907 A are possible with ∼ 12‐MW/cm2 optical pump power density from a nitrogen laser.
400 citations
TL;DR: In this paper, the phase change from amorphous to crystalline state is not only a thermal phenomenon but is directly influenced by the creation of excess electron-hole carriers by either the light, or, for the electrical device, by the electric field.
Abstract: We have observed a high-speed crystallization of amorphous semiconductor films and the reversal of this crystallization back to the amorphous state using short pulses of laser light and evidenced by a sharp change in optical transmission and reflection. This optical switching behavior is analogous to the memory-type electrical switching effect in these materials which has received wide attention1 since the observation by S. R. Ovshinsky2 of both threshold and memory switching in amorphous semiconductors. In this letter, we propose a model which closely relates the optical and electrical switching behavior, and shows that the phase change from amorphous to crystalline state is not only a thermal phenomenon but is directly influenced by the creation of excess electron-hole carriers by either the light, or, for the electrical device, by the electric field. The reversibility of the phenomenon in this model is obtained through the large difference in crystallization rates with the light on or off.
393 citations
TL;DR: In this paper, the results of an investigation into techniques for obtaining erasure resistant holograms in electro-optic crystals were described, and the most successful approach made use of thermally activated ionic drift during or after recording.
Abstract: This paper describes the results of an investigation into techniques for obtaining erasure resistant holograms in electro‐optic crystals. The most successful approach made use of thermally activated ionic drift during or after recording. The samples are heated for about 30 min at 100°C to obtain optically nonerasable holograms with as much as 50% diffraction efficiency in LiNbO3 or in doped Ba2NaNb5O15.
387 citations
TL;DR: In this article, a new electro-optical effect in nematic liquid crystals with negative dielectric anisotropy is described, using sandwich cells with molecular orientation perpendicular to the electrode surface (homeotropic alignment).
Abstract: A new electro‐optical effect in nematic liquid crystals with negative dielectric anisotropy is described, using sandwich cells with molecular orientation perpendicular to the electrode surface (homeotropic alignment). In an arrangement between crossed polarizers, high‐contrast ratios have been achieved with low voltages. This effect shows a high degree of non‐linearity and thus permits the development of matrix displays without using additional non‐linear elements.
354 citations
TL;DR: In this article, infrared-pumped stimulated emission near 6700 A in BaY2F8 : Yb3+-Er3+ and at 5515 A in B3+−Ho3+ is reported.
Abstract: Infrared‐pumped stimulated emission near 6700 A in BaY2F8 : Yb3+–Er3+ and at 5515 A in BaY2F8 : Yb3+–Ho3+ is reported. In BaY2F8 : Yb3+–Er3+, oscillation takes place at 77 °K in Er3+ transitions from 4F9/2 to the highest level of the ground state at 410 cm−1. Pumping of Er3+ results predominantly from up‐conversion produced by successive energy transfers from Yb3+; direct pumping of the metastable state and higher‐lying states of Er3+ is substantially less effective than up‐conversion. Oscillation in Ho3+ occurs in a transition from 5S2 to the highest level of the ground manifold at 385 cm−1. Up‐conversion and direct pumping contribute about equally to the inversion.
307 citations
TL;DR: In this article, an efficient broadly tunable dye-laser action with a narrow line output has been demonstrated with a mirrorless laser system using distributed feedback, which was obtained from a spatial modulation of both gain and index of refraction induced by pumping a liquid organic dye solution with fringes formed by the interference of two coherent light beams.
Abstract: Efficient broadly tunable dye‐laser action with a narrow line output has been demonstrated with a mirrorless laser system using distributed feedback. The feedback was obtained from a spatial modulation of both gain and index of refraction, induced by pumping a liquid organic dye solution with fringes formed by the interference of two coherent light beams. The device was tunable over 640 A either by varying the angle between interfering pump beams or the refractive index of the dye solvent. Linewidths less than 0.01 A were measured and a peak power of 36 kW was observed.
TL;DR: In this article, the authors observed far infrared radiation generated by picosecond pulses in LiNbO3 with several different phase-matching conditions, and deduced the laser pulsewidth from these measurements was about 2 psec in comparison with 5 psec obtained from two-photon fluorescence measurements.
Abstract: We have observed far‐infrared radiation generated by picosecond pulses in LiNbO3 with several different phase‐matching conditions. The output spectra, analyzed by a far‐infrared Michelson interferometer and by a Fabry‐Perot interferometer, agree well with theoretical calculations. The laser pulsewidth deduced from these measurements was about 2 psec in comparison with 5 psec obtained from two‐photon fluorescence measurements.
TL;DR: In this article, a new dipping technique is described for producing uniform thickness low-defect-density magnetic garnet films suitable for bubble-domain devices, based on the observation that melts having the appropriate flux and garnet composition can be supercooled over a large temperature range and will remain super-cooled, permitting the growth at constant temperature of epitaxial magnetic nanoparticles.
Abstract: A new dipping technique is described for producing uniform‐thickness low‐defect‐density magnetic garnet films suitable for bubble‐domain devices. The technique is based on the observation that melts having the appropriate flux and garnet composition can be supercooled over a large temperature range and will remain supercooled, permitting the growth at constant temperature of epitaxial magnetic garnet films.
TL;DR: In this article, Si was diffused along the evaporated Al layer of an integrated-circuit structure at temperatures between 360 and 560 °C, and the resulting concentration profile analyzed by electron microprobe.
Abstract: Si was diffused along the evaporated Al layer of an integrated-circuit structure at temperatures between 360 and 560 °C, and the resulting concentration profile analyzed by electron microprobe. The Si solubility was found to agree with literature values for Si in wrought Al. The Si diffusivity was found to be substantially enhanced, however, probably due to a high density of imperfections in the evaporated Al film. Our measured diffusivities indicate an activation energy EA ~= 0. 8 eV, about 40% less than the value for Si in wrought Al.
TL;DR: In this article, it was shown that GaN is a direct band-gap semiconductor with Eg∼3.50 eV at 2°K and that it exhibits very high gain (g∼105 cm−1) in the stimulated emission.
Abstract: Stimulated emission and laser action have been observed near 3.45 eV in single‐crystal needles of GaN. These observations support the earlier suggestion that GaN is a direct band‐gap semiconductor with Eg∼3.50 eV at 2°K. Furthermore, the occurrence of very high gain (g∼105 cm−1) in the stimulated emission emphasizes the possible device potential of this material.
TL;DR: In this paper, the backscattering method is employed to obtain microscopic information about solid-solid reactions of Si with thin layers (500-2000 A) of both vacuum-evaporated Au and sputtered Pt.
Abstract: The backscattering method is employed to obtain microscopic information about solid‐solid reactions of Si with thin layers (500–2000 A) of both vacuum‐evaporated Au and sputtered Pt. A remarkable observation is the migration of Si atoms into Au and Pt at relatively low temperatures (150 and 350 °C, respectively). Migration of Si in Pt induces first the formation of Pt2Si‐like compounds and then PtSi. In the Au–Si system, on the other hand, Si moves through and accumulates on the Au surface in the form of SiO2 under an oxidizing heat‐treatment atmosphere.
TL;DR: In this article, the origin of laser-induced refractive changes (laser damage) in LiNbO3 has been identified as iron impurities, which were measured using holographic techniques as the iron impurity content of crystals was varied.
Abstract: The origin of laser‐induced refractive changes (laser damage) in LiNbO3 has been identified as iron impurities. Quantitative measurements of the damage were made using holographic techniques as the iron impurity content of crystals was varied. Holographic diffraction efficiencies from as high as 0.44 to lower than 10−6 have been achieved with crystals 0.2 cm thick, using 10 W/cm2 of 5145‐A radiation, both by varying the iron impurity concentration and by varying the valence state of these impurities. The previously observed effects of field annealing, crystal coloration, oxidation and reduction, and the role of OH‐ ions are all accounted for.
TL;DR: In this paper, the authors show that half of the implanted atoms are incorporated into microregions of SiC which are surrounded by bulk silicon, and that SiC is observed to form at temperatures ≈ 850°C.
Abstract: The production of SiC in single‐crystal silicon by C12+ implantation to fluences of 1017/cm2‐side followed by annealing has been detected by the characteristic infrared absorption of the TO phonon of SiC. Immediately following room‐temperature implantation and after 20‐min isochronal anneals up to temperatures ≤ 825°C, a previously unreported broad absorption band centered at 700–725 cm−1 is observed. SiC is observed to form at temperatures ≈ 850°C. For anneals ≥ 850°C, most of the broad absorption band shifts into the SiC‐TO phonon absorption band. From the infrared absorption measurements together with the results of He+ backscattering, we conclude that about half of the implanted atoms are incorporated into microregions of SiC which are surrounded by bulk silicon.
TL;DR: In this paper, a triglycine sulfate (TGS) grown from solutions containing alanine was found to give biased ferroelectric hysteresis loops.
Abstract: Crystals of triglycine sulfate (TGS) grown from solutions containing alanine are found to give biased ferroelectric hysteresis loops. The material is therefore always in a fully poled state when below its Curie point in the absence of large external fields. The values of e′ and e″ are lower than for pure TGS. Pyroelectric infrared detectors using this material approach within an order of magnitude of the limit of sensitivity for uncooled thermal detectors.
TL;DR: In this article, a Nd: YAG laser has been operated under strong thermal focusing and birefringent conditions and has yielded both linearly polarized output with negligible power loss and TEM00 output of 50-70% of the multimode power.
Abstract: A Nd: YAG laser has been operated under strong thermal focusing and birefringent conditions and has yielded both linearly polarized output with negligible power loss and TEM00 output of 50–70% of the multimode power. The laser consisted of two Nd: YAG rods separated by a 90° crystal quartz polarization rotator together with a convex mirror and used no special cooling techniques. The performance of this laser, which agreed with theoretical predictions, indicates that this design approach may be generally applicable to the problem of thermally induced aberrations in such systems.
TL;DR: In this paper, preliminary results of experiments involving the storage of high efficiency holograms in evaporated thin films of arsenic trisulfide (As2S3) were reported.
Abstract: This letter reports preliminary results of experiments involving the storage of high‐efficiency holograms in evaporated thin films of arsenic trisulfide (As2S3). Both simple gratings and holograms of complex data masks have been recorded in the films by direct exposure with no subsequent processing. Diffraction efficiencies of up to 80% have been measured for two‐beam gratings. Several possible mechanisms are suggested to explain the observed results.
TL;DR: In this article, a new type of gas laser is described, which is guided by a hollow dielectric waveguide, which also serves to confine the discharge of the laser.
Abstract: This letter describes a new type of gas laser. The laser light is guided in a hollow dielectric waveguide which also serves to confine the discharge. Operation of such a laser with He–Ne mixtures at 6328 A is reported and some characteristics of the laser operation are described.
TL;DR: In this paper, the positive ions incident on the substrate plane in a planar diode discharge system were observed with an electrostatic deflection energy analyzer and a quadrupole mass spectrometer.
Abstract: The positive ions incident on the substrate plane in a planar diode discharge system are observed with an electrostatic deflection energy analyzer and a quadrupole mass spectrometer. Several targets have been rf sputtered in rare‐gas discharges and the mass spectra that are obtained indicate that the sputtered species, which leave the target predominantly as neutrals, are subsequently ionized in the discharge by Penning ionization rather than by electron‐impact ionization or other ion‐molecule reactions.
TL;DR: In this paper, the dielectric constants and refractive indices of a 5PbO · 3GeO2 crystal, which was grown from the melt by by the Czochralski method, were measured as a function of temperature.
Abstract: Dielectric constants and refractive indices of a 5PbO · 3GeO2 crystal, which was grown from the melt by by the Czochralski method, were measured as a function of temperature. The crystal was identified as a new type of ferroelectric with spontaneous polarization Ps = 0.046 C/m2, coercive field Ec ∼ 2.3 × 106 V/m at room temperature, and Tc = 177°C.
TL;DR: An acoustic shear surface wave can be guided by the interface of two semi-infinite media in contact if one, at least, of these two media is piezoelectric.
Abstract: An acoustic shear surface wave can be guided by the interface of two semi‐infinite media in contact if one, at least, of these two media is piezoelectric. After a study of the surface‐wave characteristics, the existence conditions are stated. For example, such a wave can propagate along the interface of two identical crystals, in class 6 mm, when the C axes of these crystals, both parallel to the interface and perpendicular to the propagation direction, are in opposite directions.
TL;DR: In this article, the optical and nonlinear optical properties of a new nonlinear crystal CdGeAs2 have been presented for second harmonic generation and parametric interactions over most of its transparency range from 24 to 18 μm.
Abstract: In this paper, we present the optical and nonlinear optical properties of a new nonlinear crystal CdGeAs2 The chalcopyrite structure (42 m) crystal is positive birefringent with Δn equal to 01 It is phasematchable for second harmonic generation (SHG) and parametric interactions over most of its transparency range from 24 to 18 μm In addition, it has the largest known nonlinear coefficient for a phasematchable crystal with the exception of tellurium The measured nonlinear coefficient is 34 times GaAs The calculated doubling efficiency for SHG of a CO2 laser is 10 times that of tellurium The crystal promises to be a very useful nonlinear material for parametric interactions between 3 and 18 μm
TL;DR: In this article, a molecular beam epitaxy has been used for the attainment of single-crystal multiple-layer structures with alternating types of conductivities (p/n) or band-gap energies (GaAs/AlxGa1−xAs).
Abstract: Molecular‐beam epitaxy has been used successfully for the attainment of single‐crystal multiple‐layer structures with alternating types of conductivities (p/n) or band‐gap energies (GaAs/AlxGa1−xAs). Deposition by the molecular‐beam method offers the possibility of growing periodic‐structure layers with constant chemical composition profiles and controlled uniform thicknesses.
TL;DR: In this paper, the authors report on the observation of acoustic convolution, time inversion, and electronically variable delay in real time using 105 and 220 MHz surface acoustic waves in YZ-cut LiNbO3 delay rods.
Abstract: We report on the observation of acoustic convolution, time inversion, and electronically variable delay in real time using 105‐ and 220‐MHz surface acoustic waves in YZ‐cut LiNbO3 delay rods. The time inversion is a special case of correlation, where a short ``pip'' pulse will create a reflection in time for the injected input signal pulse. The conversion losses in the processing were 64–74 dB.
TL;DR: In this article, a portable magnetic gradiometer was built using an rfbiased point contact device as a sensor and a superconducting flux transformer 2.5 cm in diameter by 10 cm long to couple to the gradient of the external field.
Abstract: A portable magnetic gradiometer was built using an rf‐biased point contact device as a sensor and a superconducting flux transformer 2.5 cm in diameter by 10 cm long to couple to the gradient of the external field. The instrument is limited by fluctuations which are probably associated with an uneven boiling of the cryogenic liquids and by environmental fluctuations in some locations. It is shown that the inherent sensitivity can be increased by an order of magnitude by increasing the bias frequency from 30 to 300 MHz. A possible use of the instrument as a magnetocardiograph in an unshielded environment was demonstrated.
TL;DR: In this paper, Ho3+:YLF (LiF4) sensitized with Er3+ and Tm3+ was achieved at 2.06 μm with a threshold of 35 J and a slope efficiency of 1.3% in normal mode with an output mirror of 62% T.
Abstract: Pulsed room‐temperature laser action at 2.06 μm has been achieved using Ho3+:YLF (LiF4) sensitized with Er3+ and Tm3+. An unoptimized cavity gave a threshold of 35 J and a slope efficiency of 1.3% in normal mode with an output mirror of 62% T. A slope efficiency of 2% and a 65‐J threshold were observed in Q‐switched operation along with Q‐switched energy of >500 mJ from a 0.9×⅛‐in. rod. The sensitizer ions have broad absorption bands and transfer times (to the active ion) of 150–200 μsec.