Showing papers in "Optics Letters in 1994"
TL;DR: A new type of scanning fluorescence microscope capable of resolving 35 nm in the far field is proposed, overcome the diffraction resolution limit by employing stimulated emission to inhibit the fluorescence process in the outer regions of the excitation point-spread function.
Abstract: We propose a new type of scanning fluorescence microscope capable of resolving 35 nm in the far field. We overcome the diffraction resolution limit by employing stimulated emission to inhibit the fluorescence process in the outer regions of the excitation point-spread function. In contrast to near-field scanning optical microscopy, this method can produce three-dimensional images of translucent specimens.
5,110 citations
TL;DR: Comparison of trapping forces for latex and gold spheres demonstrates that the gradient force is the major determinant of trapping strength and that competing effects, such as scattering or radiometric forces, are relatively minor.
Abstract: Metallic objects reflect light and have generally been considered poor candidates for optical traps, particularly with optical tweezers, which rely on a gradient force to provide trapping. We demonstrate that stable trapping can occur with optical tweezers when they are used with small metallic Rayleigh particles. In this size regime, the scattering pictures for metals and dielectrics are similar, and the larger polarizability of metals implies that trapping forces are greater. The latter fact makes the use of metal particles attractive for certain biological applications. Comparison of trapping forces for latex and gold spheres demonstrates that the gradient force is the major determinant of trapping strength and that competing effects, such as scattering or radiometric forces, are relatively minor.
738 citations
TL;DR: In this article, a novel technique, based on optical coherence tomography, was described for enhanced optical sectioning in confocal microscopy, which was demonstrated and compared with the predictions of a single-backscatter theory.
Abstract: We describe a novel technique, based on optical coherence tomography, for enhanced optical sectioning in confocal microscopy. Confocal imaging deep into highly scattering media is demonstrated and compared with the predictions of a single-backscatter theory.
720 citations
TL;DR: Optical thin-film structures exhibiting high reflectivity and a nearly constant negative group-delay dispersion over frequency ranges as broad as 80 THz are presented, making these coatings well suited for intracavity dispersion control in broadband femtosecond solid-state lasers.
Abstract: Optical thin-film structures exhibiting high reflectivity and a nearly constant negative group-delay dispersion over frequency ranges as broad as 80 THz are presented. This attractive combination makes these coatings well suited for intracavity dispersion control in broadband femtosecond solid-state lasers. We address design issues and the principle of operation of these novel devices.
675 citations
TL;DR: A near-field scanning optical microscope with a metallic probe tip was developed for detecting localized photons near the surface of the fine structure of a sample and the removal of stray-light noise contribution.
Abstract: A near-field scanning optical microscope with a metallic probe tip was developed for detecting localized photons near the surface of the fine structure of a sample. In this microscope a metallic probe is used for converting the evanescent photons localized near the sample surface to the propagating scattering light wave; the scattered light is detected in the far field with external condenser optics. During the measurement the probe tip vibrates normal to the surface with an amplitude of ~5 nm at 2.5 kHz, and the light intensity modulated with this frequency is lock-in detected. This operation permits the removal of stray-light noise contribution. Experimental results of the measurements of the exponential decay of the evanescent field produced by total internal reflection are given with and without the probe vibration. Image data of the surface profile of an optical compact disk are also shown.
570 citations
TL;DR: A simple double-pass fiber noise measurement and control system is described, which is demonstrated to provide millihertz accuracy of noise cancellation.
Abstract: Although a single-mode optical fiber is a convenient and efficient interface/connecting medium, it introduces phase-noise modulation, which corrupts high-precision frequency-based applications by broadening the spectrum toward the kilohertz domain. We describe a simple double-pass fiber noise measurement and control system, which is demonstrated to provide millihertz accuracy of noise cancellation.
539 citations
TL;DR: Passively Q-switched 1.064-microm microchip lasers have been constructed from thin pieces of Nd(3+):YAG bonded to thin pieces with peak power in excess of 180 MW/cm(2) in a single-frequency TEM(00) mode.
Abstract: Passively Q-switched 1.064-microm microchip lasers have been constructed from thin pieces of Nd(3+):YAG bonded to thin pieces of Cr(4+):YAG. When pumped with the unfocused 1.2-W output of a fiber-coupled diode, these devices produced 11-microJ pulses of 337-ps duration at a pulse repetition rate of 6 kHz in a single-frequency TEM(00) mode. The peak power of the lasers was in excess of 180 MW/cm(2).
439 citations
TL;DR: A frequency-domain near-infrared tissue spectrometer capable of measuring the reduced scattering coefficient of tissue with enough precision to detect changes in glucose levels in the physiological and pathological range is designed and constructed.
Abstract: Tissue glucose levels affect the refractive index of the extracellular fluid. The difference in refractive index between the extracellular fluid and the cellular components plays a role in determining the reduced scattering coefficient (micro(s)') of tissue. Hence a physical correlation may exist between the reduced scattering coefficient and glucose concentration. We have designed and constructed a frequency-domain near-infrared tissue spectrometer capable of measuring the reduced scattering coefficient of tissue with enough precision to detect changes in glucose levels in the physiological and pathological range.
382 citations
TL;DR: A measurement technique is demonstrated that greatly reduces radiation trapping in Yb:YAG, a prototypical quasi-three-level laser medium, which results in a more-accurate radiative lifetime and a higher stimulated emission cross section.
Abstract: Radiation trapping causes significant lengthening of the measured fluorescence lifetime in optically thin solid-state laser gain media, which leads to underestimates of the stimulated emission cross section by as much as 30%. A measurement technique is demonstrated that greatly reduces radiation trapping in Yb:YAG, a prototypical quasi-three-level laser medium. The radiative lifetime of the (2)F(5/2) manifold was measured to be 0.951 ms at 300 K, which is more than 10% lower than any previous measurement. This more-accurate radiative lifetime gives a 1.03-microm peak effective stimulated emission cross section of 2.3 x 10(-20) cm(2). Our measurement technique is expected to be most relevant for three-level and quasi-three-level laser media.
378 citations
TL;DR: The reverse saturable absorption and the optical-limiting response of metal phthalocyanines can be enhanced by use of the heavy-atom effect.
Abstract: The reverse saturable absorption and optical limiting response of metal phthalocyaninies can be enhanced by using the heavy-atom effect. Phthalocyanines containing heavy metal atoms, such as In, Sn, and Pb show nearly a factor of two enhancement in the ratio of effective excited-state to ground-state absorption cross sections compared to those containing lighter atoms, such as Al and Si. In an f/8 optical geometry, homogeneous solutions of heavy metal phthalocyanines, at 30% linear transmission, limit 8-ns, 532-nm laser pulses to less than or equal to 3 (micro)J (the energy for 50% probability of eye damage) for incident pulses up to 800 (micro)J.
375 citations
TL;DR: Nonlinear photorefraction in pure aligned nematic liquid crystals in the presence of an applied dc electric field is reported, attributed to nematic axis reorientation created by the photoinduced space-charge field in combination with the applied dc field.
Abstract: We report the observation of nonlinear photorefraction in pure aligned nematic liquid crystals in the presence of an applied dc electric field The effect is attributed to nematic axis reorientation created by the photoinduced space-charge field in combination with the applied dc field Strong optical nonlinearity, self-diffraction, and beam-coupling effects are observed
TL;DR: A new pulse-shaping technique, using an acousto-optic modulator as a spatial modulator in a zero-dispersion delay line that simplifies optical alignment and dramatically improves update rates.
Abstract: We demonstrate a new pulse-shaping technique, using an acousto-optic modulator as a spatial modulator in a zero-dispersion delay line. Compared with existing techniques, this approach simplifies optical alignment and dramatically improves update rates. It should also improve flexibility for generating complex waveforms.
TL;DR: A scheme for encoding digital data within a spiky chaotic carrier from a loss-modulated solid-state laser that is performed in real time with a synchronized chaotic laser system.
Abstract: We propose a scheme for encoding digital data within a spiky chaotic carrier from a loss-modulated solid-state laser. Decoding is performed in real time with a synchronized chaotic laser system.
TL;DR: A method of multiplexing holograms by rotating the material or, equivalently, the recording beams is described, and a total of 295 holograms in a 38-microm-thick photopolymer film is multiplexed by combining peristrophicmultiplexing with angle multiplexers.
Abstract: A peristrophic multiplexing system directs a signal light beam and reference light beam onto a selected recording spot in the recording medium. The light beams collectively define a plane of interaction. Either the recording medium or the signal/reference beam are rotated relative to the other through a succession of peristrophic multiplexing angles. Those angles cause relative rotation about an axis that is not perpendicular to the plane of selectivity. The rotation occurs contemporaneously with the modulating of the hologram on the medium.
TL;DR: This work reports what is to their knowledge the first fiber distributed-feedback laser using a single Bragg grating at 1.5 microm written directly into a 2-cm-long Er(3+)-doped fiber codoped with Yb( 3+).
Abstract: We report what is to our knowledge the first fiber distributed-feedback laser using a single Bragg grating at 1.5 microm written directly into a 2-cm-long Er(3+)-doped fiber codoped with Yb(3+). We obtained robust single-frequency operation by either using one end reflector or locally heating the center of the grating to create the necessary phase shift.
TL;DR: A linearly chirped in-fiber Bragg grating is reported that can compensate at 1549 nm for the dispersion of standard telecommunications optical fiber optimized for 1300-nm operation.
Abstract: A linearly chirped in-fiber Bragg grating is reported that can compensate at 1549 nm for the dispersion [ approximately -19 ps/(nmkm)] of standard telecommunications optical fiber optimized for 1300-nm operation.
TL;DR: A one-dimensional method for the absolute determination of the path difference in interferometers to obtain unique surface profiles with high accuracy is discussed.
Abstract: The usual automated interferometric profilometers suffer from phase-unwrapping problems. We discuss a one-dimensional method for the absolute determination of the path difference in interferometers to obtain unique surface profiles with high accuracy.
TL;DR: The effect of glucose on light transport in highly scattering, tissue-simulating phantoms is demonstrated both experimentally and theoretically by application of diffusion theory.
Abstract: The presence of glucose dissolved in an aqueous solution increases the refractive index of the solution and therefore has an influence on the scattering properties of any particles suspended within it. We present experimental data on the effect of glucose concentration on the scattering coefficient of a suspension of spherical polystyrene particles. The experimental results are in good agreement with Mie theory. The effect of glucose on light transport in highly scattering, tissue-simulating phantoms is demonstrated both experimentally and theoretically by application of diffusion theory. The possible application of this effect for noninvasive glucose monitoring of diabetic patients is discussed.
TL;DR: Fractional-order Fourier transforms are adapted to the mathematical expression of Fresnel diffraction, just as the standard Fourier transform is adapted to Fraunhofer diffraction.
Abstract: Fractional-order Fourier transforms are adapted to the mathematical expression of Fresnel diffraction, just as the standard Fourier transform is adapted to Fraunhofer diffraction. The continuity of fractional Fourier transforms with respect to their orders corresponds to the continuity of wave propagation, and their composition is in accordance with the Huygens principle.
TL;DR: In this paper, a modification to the Z-scan technique was introduced that results in a sensitivity enhancement that permits measurement of nonlinearly induced wavefront distortion of ≃λ/104.
Abstract: We introduce a simple modification to the Z-scan technique that results in a sensitivity enhancement that permits measurement of nonlinearly induced wave-front distortion of ≃λ/104. This sensitivity was achieved with 10-Hz repetition-rate pulsed laser sources. Sensitivity to nonlinear absorption is also enhanced by a factor of ≃3. This method permits characterization of nonlinear thin films without the need for waveguiding.
TL;DR: By operating near the zero second- and third-order dispersion point in a self-mode-locked Ti:sapphire laser the authors can generate sub-10-fs pulses and demonstrate that the pulse is shortest near the middle of the laser crystal, in one direction of propagation.
Abstract: We demonstrate that by operating near the zero second- and third-order dispersion point in a self-mode-locked Ti:sapphire laser we can generate sub-10-fs pulses. Our numerical simulations show that the pulse duration is limited by fourth-order dispersion and that shorter pulses will be possible if this can be reduced. Also, by inserting a pellicle in various positions in a Ti:sapphire cavity, we have measured the intracavity pulse duration and chirp of the circulating pulse in the laser. Our results demonstrate that the pulse is shortest near the middle of the laser crystal, in one direction of propagation. In the other direction of propagation, the pulse is positively chirped and several times longer.
TL;DR: It is shown that ideal reflection filters can be designed by combining guided-mode resonance effects in waveguide gratings with antireflection effects of thin-film structures and a single-layer filter with multilayer design.
Abstract: We show that ideal reflection filters can be designed by combining guided-mode resonance effects in waveguide gratings with antireflection effects of thin-film structures. Since the guided-mode resonance effect overrides the antireflection effect this filter provides a symmetrical line shape with near-zero reflectivity over appreciable wavelength bands adjacent to the resonance wavelength. In the single-layer filter the same layer functions as the waveguide grating supporting the resonance and as the antireflection layer suppressing reflection around the resonance. A multilayer design allows the filter resonance peak to have a wide surrounding region of low reflectance. The central resonance wavelength, the filter linewidth, the range of the low sidebands, and the resonance line shape are all under the control of the designer.
TL;DR: A new operation is presented, which is the Lorentz-type hyperbolic transformation in phase space and exhibits squeezing, which shows that the SAFT including these five operations can be generated from any two independent operations.
Abstract: The special affine Fourier transformation (SAFT) is a generalization of the fractional Fourier transformation (FRT) and represents the most general lossless inhomogeneous linear mapping, in phase space, as the integral transformation of a wave function. Here we first summarize the most well-known optical operations on light-wave functions (i.e., the FRT, lens transformation, free-space propagation, and magnification), in a unified way, from the viewpoint of the one-parameter Abelian subgroups of the SAFT. Then we present a new operation, which is the Lorentz-type hyperbolic transformation in phase space and exhibits squeezing. We also show that the SAFT including these five operations can be generated from any two independent operations.
TL;DR: By using a high-resistance thin-film layer of amorphous silicon under the 98-element parallel electrode structure layer, this work generates a near-continuous index perturbation to form a cylindrical lens.
Abstract: A 1 mm × 1 mm nematic liquid-crystal three-terminal device for optical beam forming (focusing/spoiling) is fabricated. A thin-film-resistor network on the device substrate layer is used to control the voltages on the 98 internal lens electrodes by use of only one variable external driver. By using a high-resistance thin-film layer of amorphous silicon under the 98-element parallel electrode structure layer, we generate a near-continuous index perturbation to form a cylindrical lens. The focal length of this lens is continuously variable from inifinity to 12 cm by use of a variable 1–4-V-peak 1-kHz square-wave external terminal control signal.
TL;DR: This work uses the algorithmic method of generalized projections (GP's) to retrieve the intensity and phase of an ultrashort laser pulse from the experimental trace in frequency-resolved optical gating (FROG).
Abstract: We use the algorithmic method of generalized projections (GP's) to retrieve the intensity and phase of an ultrashort laser pulse from the experimental trace in frequency-resolved optical gating (FROG). Using simulations, we show that the use of GP's improves significantly the convergence properties of the algorithm over the basic FROG algorithm. In experimental measurements, the GP-based algorithm achieves significantly lower errors than previous algorithms. The use of GP's also permits the inclusion of an arbitrary material response function in the FROG problem.
TL;DR: A high-spectral-resolution lidar that uses an iodine absorption filter and a tunable, narrow-bandwidth Nd:YAG laser is demonstrated and provides better performance than the Fabry–Perot etalon that it replaces.
Abstract: A high-spectral-resolution lidar that uses an iodine absorption filter and a tunable, narrow-bandwidth Nd:YAG laser is demonstrated. Measurements of aerosol scattering cross section and optical depth are presented. The iodine absorption filter provides better performance than the Fabry–Perot etalon that it replaces.
TL;DR: A diffractive laser cavity mirror is described that can customize the amplitude and phase of a laser mode and has a large discrimination against higher-order modes.
Abstract: A diffractive laser cavity mirror is described that can customize the amplitude and phase of a laser mode. The design of this diffractive element is shown for a square, flat-topped fundamental mode. The laser cavity has a theoretical fundamental mode loss of only 0.08% and a second-order mode loss of 48.2%, resulting in high modal discrimination. The fabricated mirror is tested in a Nd:YAG laser system. The resulting square flat-topped mode has an rms variation of 1.5% over the two-dimensional flat-topped region and a large discrimination against higher-order modes.
TL;DR: The operation of a semiconductor laser amplifier is described as a nonlinear element, using a novel three-wavelength configuration, which enhances the recovery rate of the nonlinear refractive index and permits choice of its sign and magnitude.
Abstract: We describe the operation of a semiconductor laser amplifier as a nonlinear element, using a novel three-wavelength configuration, which enhances the recovery rate of the nonlinear refractive index and permits choice of its sign and magnitude. Simple rate-equation analysis suggests that 100-GHz operation should be possible with powers of ~1 W.
TL;DR: The nonlinear refractive index, n(2), of the glass found in silica-core and dispersion-shifted optical fibers is accurately measured and is found to be 2.36 x 10(-16) cm(2)/W (+/-5%), respectively.
Abstract: We have accurately measured the nonlinear refractive index, n2, of the glass found in silica-core and dispersion-shifted optical fibers. We find that at 1.319 µm the n2 of silica-core and dispersion-shifted fibers is 2.36 × 10−16 and 2.52 × 10−16 cm2/W (±5%), respectively. We also estimate that the n2 of germania is three times the n2 of pure silica. Because the wavelength dependence of n2 between 1.3 and 1.5 µm is known to be small, our measured values should also be valid at 1.55 µm.
TL;DR: This work has demonstrated cw laser operation at wavelengths near 3 microm from monolithic, Er-doped YSGG, GGG, and YAG lasers by direct upper-state pumping in the 0.97-microm wavelength region with either a Ti:sapphire laser or InGaAs diode lasers.
Abstract: We have demonstrated cw laser operation at wavelengths near 3 μm from monolithic, Er-doped YSGG, GGG, and YAG lasers by direct upper-state pumping in the 0.97-μm wavelength region with either a Ti:sapphire laser or InGaAs diode lasers. We have obtained slope efficiencies as high as 31% and, with diode-laser pumping, output powers of 0.5 W. In addition, we have demonstrated tunable single-frequency operations from Er:YAG.