Showing papers in "Optics Letters in 1985"
TL;DR: A nonplanar ring oscillator with the resonator contained entirely within a Nd:YAG crystal obtained unidirectional oscillation when placed in a magnetic field with pump-limited, single-axial-mode output of 163 mW.
Abstract: We have built a nonplanar ring oscillator with the resonator contained entirely within a Nd:YAG crystal. When the oscillator was placed in a magnetic field, unidirectional oscillation was obtained with a pump-limited, single-axial-mode output of 163 mW.
613 citations
TL;DR: It is shown that the optical phase-conjugated reflectivity from silver and gold colloids is enhanced by several orders of magnitude and this enhancement is traced to the nonlinearities of the electrons in the metal particles and the value of their optical Kerr-effect coefficient is extracted.
Abstract: We show that the optical phase-conjugated reflectivity from silver and gold colloids is enhanced by several orders of magnitude. The reflectivity on resonance is comparable with that of CS(2) for metal-particle volume concentration of a few parts in 10(6). We trace this enhancement to the nonlinearities of the electrons in the metal particles and extract the value of their optical Kerr-effect coefficient.
527 citations
TL;DR: The remarkable collective computational properties of the Hopfield model for neural networks are reviewed, including recognition from partial input, robustness, and error-correction capability.
Abstract: The remarkable collective computational properties of the Hopfield model for neural networks [Proc. Nat. Acad. Sci. USA 79, 2554 (1982)] are reviewed. These include recognition from partial input, robustness, and error-correction capability. Features of the model that make its optical implementation attractive are discussed, and specific optical implementation schemes are given.
400 citations
TL;DR: An ultrasbort-pulse laser is described that, under specific operating conditions, balances the mechanisms of conventional passive mode locking and solitonlike pulse shaping in a single resonator to generate optical pulses that are to the authors' knowledge the shortest yet emitted directly from a laser.
Abstract: We describe an ultrasbort-pulse laser that, under specific operating conditions, balances the mechanisms of conventional passive mode locking and solitonlike pulse shaping in a single resonator to generate optical pulses that are to our knowledge the shortest yet emitted directly from a laser, 27 fsec.
381 citations
TL;DR: Stimulated Raman scattering from an individual liquid droplet has been observed and the occurrence of a series of spectrally narrow peaks that are regularly spaced in wavelength is consistent with morphology-dependent resonances of the droplet, which acts as an optical resonator.
Abstract: Stimulated Raman scattering (SRS) from an individual liquid droplet (~30-microm radius) has been observed for H(2)O, D(2)O, and ethanol. The occurrence of a series of spectrally narrow peaks that are regularly spaced in wavelength is consistent with morphology-dependent resonances of the droplet, which acts as an optical resonator. The input intensity required to achieve the SRS threshold for the droplet is considerably less than that for the liquid in an optical cell.
317 citations
TL;DR: Measurements of the two-photon absorption coefficients beta(2) of 10 different semiconductors having band-gap energies between 1.4 and 3.7 eV find that beta( 2) varies as E(g)(-3), as predicted by theory.
Abstract: We present measurements of the two-photon absorption coefficients /2 of 10 different semiconductors having band-gap energies between 1.4 and 3.7 eV. We find that 12 varies as Eg- 3 , as predicted by theory. In addition, the absolute values of 02 agree with theory, which includes the effect of nonparabolic bands, the average difference being less than 26%. This agreement permits confident predictions of two-photon absorption coefficients of other materials at other wavelengths. The ever-increasing role of semiconductors in lightwave technology has created a pressing demand for the characterization of the nonlinear-optical properties of these materials. Semiconductors are attractive as elements in nonlinear-optical devices because of their large and potentially extremely fast optical nonlinearities. A careful study of these macroscopic nonlinearities should allow one to determine the dependence of these nonlinearities on fundamental microscopic mechanical and electronic material properties (e.g., band gap, carrier lifetime, carrier effective mass). The data base formed by this information would then allow one not only to tabulate the materials that exhibit large nonlinearities but also to predict the specific material parameters that give rise to these high nonlinearities. This predictive capability is extremely important from the standpoint of searching for materials with large nonlinearities. A study of the nonlinear-optical properties of several semiconductors is presented here, and a relationship between the two-photon absorption coefficient (/32) and other material properties is verified. Ten different materials were experimentally studied for which the incident photon energy hw is less than the direct band-gap energy Eg but greater than Eg/2, so that two-photon absorption (2PA) is allowed.' Both 1.06and 0.53-jum picosecond pulses are used in transmission experiments, similar to those used previously by Bechtel and Smith, 2 on semiconductors with Eg ranging from 1.4 to 3.7 eV. We find that 02 is given by
314 citations
TL;DR: In a scanning laser microscope detecting fluorescent light from the specimen, the depth-discriminating property of confocal scanning has been used to carry out optical slicing of a thick specimen.
Abstract: In a scanning laser microscope detecting fluorescent light from the specimen, the depth-discriminating property of confocal scanning has been used to carry out optical slicing of a thick specimen. The recorded digital images constitute a three-dimensional raster covering a volume of the specimen. The specimen has been visualized in stereo and rotation by making look-through projections of the digital data in different directions. The contrast of the pictures has been enhanced by generating the gradient volume. This permits display of the border surfaces between regions instead of the regions themselves.
283 citations
TL;DR: A new effect appears in femtosecond optical pulse compression, using single-mode fibers, that is described as optical wave breaking, which often leads to computational instabilities, but careful numerical simulations give results in excellent agreement with experiment.
Abstract: A new effect appears in femtosecond optical pulse compression, using single-mode fibers, that we describe as optical wave breaking. In the fiber, frequency-shifted light in the leading and trailing edges of a pulse overtakes unshifted light in the pulse tails. Mixing of these overlapping frequency components generates sidelobes on the pulse spectrum. The effect often leads to computational instabilities, but careful numerical simulations, including fiber loss, give results in excellent agreement with experiment.
249 citations
TL;DR: The temporal profile of ultrashort optical pulses may be tailored by physically manipulating the phase and the amplitude of frequency components that are spatially dispersed within a grating pulse compressor by generating a burst of evenly spaced picosecond pulses.
Abstract: The temporal profile of ultrashort optical pulses may be tailored by physically manipulating the phase and the amplitude of frequency components that are spatially dispersed within a grating pulse compressor. Arbitrary pulse shapes may be synthesized subject only to the usual restrictions imposed by finite bandwidth and spatial resolution. We demonstrate this technique by generating a burst of evenly spaced picosecond pulses, a pulse doublet with odd field symmetry, and a burst of evenly spaced pulse doublets with odd field symmetry.
248 citations
TL;DR: The design and test of a laser-diode-pumped monolithic Nd:YAG oscillator found the frequency jitter was less than 10 kHz over a 0.3-sec period, the best frequency stability reported for a Nd?:YAG laser to date.
Abstract: We have designed and tested a laser-diode-pumped monolithic Nd:YAG oscillator. The electrical-to-optical slope efficiency was 6.5%. The frequency jitter was less than 10 kHz over a 0.3-sec period, the best frequency stability reported for a Nd:YAG laser to date.
223 citations
IBM1
TL;DR: In this article, the photon-gated spectral hole burning was observed in BaClF:Sm(2+) with the presence of an additional gating light source, and the hole widths of 25 MHz at 2 K were shown to be much narrower than the inhomogeneous broadening of 16 GHz.
Abstract: We have observed photon-gated spectral hole burning, i.e., hole burning that occurs only in the presence of an additional gating-light source. Gating enhancement factors of 10(4) were observed. In BaClF:Sm(2+) this involves two step photoionization of Sm(2+) and leads to persistent holes in the (4)F(0) --> (5)D(0) (687.9-nm) and (7)F(0) --> (5)D(1) (629.7-nm) absorption lines. The hole widths of 25 MHz at 2 K are much narrower than the inhomogeneous broadening of 16 GHz. The action spectrum of the gating shows a threshold behavior around 2.5 eV. Erasing studies show that Sm(3)+ acts as a trap for the released electrons. A remarkable and novel feature is that the holes can be recovered after temperature cycling to 300 K.
TL;DR: A new photopolarimeter for the simultaneous measurement of all four Stokes parameters of light is described, which can be either computed or determined by calibration for a given arrangement of four detectors.
Abstract: A new photopolarimeter for the simultaneous measurement of all four Stokes parameters of light is described. The light beam, whose state of polarization is to be determined, strikes at oblique incidence three photodetector surfaces in succession, each of which is partially specularly reflecting and each of which generates an electrical signal proportional to the fraction of the radiation that it absorbs. A fourth photodetector captures the remainder of the light. The four outputs thus developed form a 4 x 1 signal vector I, which is linearly related, I = AS, to the input Stokes vector S. Consequently, S is obtained by S = A(-1)I. The 4 x 4 instrument matrix A must be nonsingular, and this requires that the light beam not remain in one plane. For a given arrangement of four detectors, A can be either computed or determined by calibration. The advantages of this polarimeter are enumerated.
TL;DR: It is discovered that the extremely inexpensive Radio Shack liquid-crystal television, with proper modifications, has potential for optical-data-processing applications.
Abstract: The potential of the extremely inexpensive Radio Shack liquid-crystal television (LCTV) as a two-dimensional spatial light modulator has been investigated. The LCTV modulates the transmission of coherent or incoherent light and can either be electronically addressed through a microcomputer or optically addressed with a TV camera. We have measured the transmission characteristics of the device, examined its diffraction pattern, and tested its use as an input device for an optical correlator. We have discovered that, with proper modifications, it has potential for optical-data-processing applications.
TL;DR: A single-pulse, laser-induced-fluorescence diagnostic for the measurement of two-dimensional temperature fields in combustion flows is described, using sheet illumination from a tunable laser to excite planar laserinduced fluorescence in a stable tracer molecule.
Abstract: A single-pulse, laser-induced-fluorescence diagnostic for the measurement of two-dimensional temperature fields in combustion flows is described. The method uses sheet illumination from a tunable laser to excite planar laser-induced fluorescence in a stable tracer molecule, seeded at constant mole fraction into the flow field. The temporal resolution of this technique is determined by the laser pulse length. Experimental results are presented for a rod-stabilized, premixed methane–air flame, using the Q1(22) line of the nitric oxide A2 ∑+(v = 0) ← X2Π1/2(v = 0) transition (λ ≃ 225.6 nm).
TL;DR: With sufficient Raman gain to compensate exactly for net fiber energy loss, distortionless propagation of 10-psec FWHM fundamental soliton pulses over a 10-km length of single-mode fiber is demonstrated.
Abstract: With sufficient Raman gain to compensate exactly for net fiber energy loss, we have demonstrated distortionless propagation of 10-psec FWHM fundamental (N = 1) soliton pulses (λ = 1.56 μm) over a 10-km length of singlemode fiber. The implications of this experiment for development of an all-optical, high-bit-rate, long-distance telecommunications system are discussed briefly.
TL;DR: A new method of monitoring skin blood flow is proposed based on a temporal spectral analysis of the speckle signal, which shows promising results in terms of temporal statistics and efficiency.
Abstract: The temporal statistics of laser speckle from vascular tissues on skin surface have been measured. Based on a temporal spectral analysis of the speckle signal, a new method of monitoring skin blood flow is proposed.
TL;DR: In this paper, the authors demonstrate optical-beam phase conjugation by the process of two-beam coupling in photorefractive barium titanate and show that the incident, image-bearing beam causes exponential gain for counter-propagating waves, which are fed by noise and emerge with a power of the order of 10% of the incident beam.
Abstract: We demonstrate optical-beam phase conjugation by the process of two-beam coupling in photorefractive barium titanate The incident, image-bearing beam causes exponential gain for counterpropagating waves, which are fed by noise and emerge with a power of the order of 10% of the incident beam and phase conjugate to it This is expected from the calculated plane-wave gain plus the analogy to the theory of phase conjugation of complex wave fronts by stimulated Brillouin backscattering We conjugate beams at either 515 or 488 nm at between 10- and 50-mW power, and find, as expected, no frequency shift (<1 Hz) in the process
TL;DR: A method of using the full G-matrix approach for the calculation of these spectra that is both exact and computationally efficient (requiring only one matrix diagonalization and inversion per spectrum) is discussed and excellent agreement with experimental data is obtained.
Abstract: High-resolution coherent anti-Stokes Raman spectroscopy spectra of the N(2) Q branch at 294 K have been obtained at 1, 5, and 10 atm. Even at 1-atm pressure, disagreements with spectra calculated using the isolated line approximation were observed, indicating the importance of collisional narrowing effects in describing these spectra. A method of using the full G-matrix approach for the calculation of these spectra that is both exact and computationally efficient (requiring only one matrix diagonalization and inversion per spectrum) is discussed. Excellent agreement with experimental data is obtained using this method and a simple exponential gap model for the off-diagonal G-matrix elements.
TL;DR: Simultaneous imaging of laser-induced fluorescence in three selected wavelength bands from hematoporphyrin-derivative-bearing tissue has been performed, permitting considerable contrast enhancement for cancer-tumor localization.
Abstract: Simultaneous imaging of laser-induced fluorescence in three selected wavelength bands from hematoporphyrin-derivative-bearing tissue has been performed, permitting considerable contrast enhancement for cancer-tumor localization.
TL;DR: It is reported that coherent oscillations due to self-induced moving gratings in photorefractive BSO crystals when recording with an external applied field is reported.
Abstract: We report coherent oscillations due to self-induced moving gratings in photorefractive BSO crystals when recording with an external applied field. Different types of ring and phase-conjugate resonators pumped with low-incident-intensity beams and having short response times are demonstrated. The conditions permitting oscillation and the respective frequencies of the pump and the signal beams in the cavity are analyzed.
TL;DR: Infrared supercontinua spanning the range 3-14 microm were observed when an intense pulse generated from a CO(2) laser was passed into GaAs, AgBr, ZnSe, and CdS crystals, qualitatively compared with theoretical predictions.
Abstract: Infrared supercontinua spanning the range 3-14 microm were observed when an intense pulse generated from a CO(2) laser was passed into GaAs, AgBr, ZnSe, and CdS crystals. These supercontinua have been qualitatively compared with theoretical predictions.
TL;DR: Gaussian modes with large sections have been experimentally produced in Cassegrain resonators using Gaussian reflectivity convex couplers and the far field of the beam, which was coupled through a Gaussian coupler, was found to be free from secondary rings.
Abstract: Gaussian modes with large sections have been experimentally produced in Cassegrain resonators using Gaussian reflectivity convex couplers. The far field of the beam, which was coupled through a Gaussian coupler, was found to be free from secondary rings.
TL;DR: Mode indices measurements made on planar waveguides by K(+)-ion exchange in soda-lime glass substrates were directed toward establishing formulas for evaluating the effective guide depth and diffusion constant for both the TE and the TM modes, given the diffusion temperature and time.
Abstract: Mode indices measurements for both the TE and TM modes have been made on planar waveguides by K+-ion exchange in soda-lime glass substrates. These were directed toward establishing formulas for evaluating the effective guide depth and diffusion constant for both the TE and the TM modes, given the diffusion temperature and time. The corresponding surface-index change can also be determined.
TL;DR: The coherent Raman mixing spectra from individual micrometer-sized droplets of ethanol and of water consist of regularly spaced peaks that correspond to the morphology-dependent resonances of a spherical droplet, while the coherent anti-Stokes Raman scattering specta from droplets exhibit no morphology- dependent peaks.
Abstract: The coherent Raman mixing spectra from individual micrometer-sized droplets of ethanol and of water consist of regularly spaced peaks that correspond to the morphology-dependent resonances of a spherical droplet. In contrast, the coherent anti-Stokes Raman scattering spectra from droplets exhibit no morphology-dependent peaks. Both results are explained by the spatial overlap of the enhanced internal field distributions and by the phase-matching conditions associated with the droplet.
TL;DR: Optical double-resonance experiments on N3 centers provided direct evidence for a (2)A metastable level and results in rapid decay of the excited ( 2)E state and low quantum efficiency as well as significant excited-state absorption in the N3 luminescence region.
Abstract: Laser action at 530 nm using H3 centers in diamond was observed with an efficiency of 13.5% at room temperature. Optical double-resonance experiments on N3 centers provided direct evidence for a 2A metastable level. Its presence results in rapid decay of the excited 2E state and low quantum efficiency as well as significant excited-state absorption in the N3 luminescence region.
TL;DR: A new technique has been developed that permits simultaneous two-dimensional mapping of two scalar components in a turbulent reacting flow that uses two optical multichannel analyzers, each of which detects light scattered by a different mechanism and thus provides different information.
Abstract: A new technique has been developed that permits simultaneous two-dimensional mapping of two scalar components (e.g., species and temperature) in a turbulent reacting flow. The technique uses two optical multichannel analyzers, each of which detects light scattered by a different mechanism (e.g., Rayleigh and Raman) and thus provides different information. The technique has been applied to both premixed and nonpremixed flames, and results are reported for each. The simultaneous information obtained in these experiments should provide new data on the interaction of turbulence and combustion in these chemically reacting flows.
TL;DR: In this article, continuous wave lasing has been obtained on the 2 → 1 vibrational transition of impurity CN− ions in KBr by optical pumping of the weakly allowed first-overtone level of the molecule with a tunable (F2+)A color-center laser.
Abstract: Continuous-wave lasing has been obtained on the 2 → 1 vibrational transition of impurity CN− ions in KBr. Population inversion is produced by optical pumping of the weakly allowed first-overtone level of the molecule with a tunable (F2+)A color-center laser.
TL;DR: A general, accurate, and explicit expression has been derived for the angular shift of a Gaussian beam that is partially reflected by a dielectric interface that holds for arbitrary incidence angles, including the vicinity of the Brewster angle and asymptotically approaches the results obtained by others for incidence away from that angle.
Abstract: A general, accurate, and explicit expression has been derived for the angular shift of a Gaussian beam that is partially reflected by a dielectric interface. This result holds for arbitrary incidence angles, including the vicinity of the Brewster angle, and asymptotically approaches the results obtained by others for incidence away from that angle. A series of reflected beam profiles is shown to clarify the angular-shift phenomenon and to illustrate the beam-distortion effect that occurs at, or near, Brewster incidence.
TL;DR: In this paper, the cleanup of spatial and temporal phase aberration using photorefractive two-wave mixing in a strontium barium niobate crystal was reported.
Abstract: Photorefractive two-wave mixing exhibits energy transfer without phase cross talk. Such a phenomenon can be used to clean up wave-front aberrations of laser beams. We report the cleanup of spatial and temporal phase aberration using photorefractive two-wave mixing in a strontium barium niobate crystal.