Transmission of a Gaussian beam through a Fabry-Perot interferometer

The transmission of a Gaussian beam through a Fabry-Perot interferometer (FPI) has been investigated. The equation for the electric field of the transmitted beam was derived and then the transmitted irradiance I(t) was numerically calculated for different selected parameters of both the FPI and the beam. The results show that the energy profile of the transmitted beam has been distorted to different degrees depending on the various parameters of the Gaussian beam and the FPI. Moreover the results show that the positions of the peaks of the transmitted beam are shifted, especially for intermediate waists for which the arctan term is nonlinear. The results also show that for nonnormal incidence successive transmitted beams are spatially separated and are not interfering appreciably with each other.     

Modulation depth of Michelson interferometer with Gaussian beam

Mirror misalignment or the tilt angle of the Michelson interferometer can be estimated from the modulation depth measured with collimated monochromatic light. The intensity of the light beam is usually assumed to be uniform, but, for example, with gas lasers it generally has a Gaussian distribution, which makes the modulation depth less sensitive to the tilt angle. With this assumption, the tilt angle may be underestimated by about 50%. We have derived a mathematical model for modulation depth with a circular aperture and Gaussian beam. The model reduces the error of the tilt angle estimate to below 1%. The results of the model have been verified experimentally.     

Laser interferometer with a high-resolution optical microscope for measuring small line scales

The optical train of an interferometer to certify small-scale measures in the range 1–200 μm with a high-resolution modulation optical microscope for sighting the lines on the measure is described. The circuit of a interference-fringe recording unit is presented. Some results of line scale measurements are reported. Translated from Izmeritel'naya Tekhnika, No 9, pp 27–29, September, 1997     

Atmospheric optical communication with a Gaussian Schell beam

We consider a wireless optical communication link in which the laser source is a Gaussian Schell beam. The effects of atmospheric turbulence strength and degree of source spatial coherence on aperture averaging and average bit error rate are examined. To accomplish this, we have derived analytic expressions for the spatial covariance of irradiance fluctuations and log-intensity variance for a Gaussian beam of any degree of coherence in the weak fluctuation regime. When spatial coherence of the transmitted source beam is reduced, intensity fluctuations (scintillations) decrease, leading to a significant reduction in the bit error rate of the optical communication link. We have also identified an enhanced aperture-averaging effect that occurs in tightly focused coherent Gaussian beams and in collimated and slightly divergent partially coherent beams. The expressions derived provide a useful design tool for selecting the optimal transmitter beam size, receiver aperture size, beam spatial coherence, transmitter focusing, etc., for the anticipated atmospheric channel conditions.     

Spatial and spectral response of a Fabry-Perot interferometer illuminated by a Gaussian beam

A generalized study has been done of the transmission characteristics of a Fabry-Perot interferometer (FPI) illuminated by a Gaussian light beam impinging on it at normal and non-normal incidence. The theoretical approach is based on a plane-wave, angular-spectrum representation of both the incident Gaussian beam and the transmitted beam. Expressions are obtained for the FPI instrumental function and for the spatial distribution of the transmitted beam. Numerical results are presented for the FPI maximum transmission, effective finesse, and spectral displacement of the interference maximum.     

Dynamics of bubbles in field access devices studied using a high speed optical sampling microscope

Dynamics of bubbles in field access devices operated at 100 kHz and 200 kHz have been studied using a high speed optical sampling microscope capable of making a 10 nsec single exposure photograph at a known sampling time with respect to a rotating field orientation. By scanning the sampling time through one rotating field cycle, a series of time-sequenced transient domain configurations of bubbles have been recorded on 16 mm film. The devices studied were commonly used permalloy propagating structures, T-bar, T-X, X-bar, and chevron fabricated on an epitaxial garnet film. From each frame of the 16 mm film, plots of the position of the leading and trailing edges of a bubble as a function of rotating field angle were made. These position plots revealed very nonuniform bubble motion in these circuits. The instantaneous velocities of the leading and trailing edges of the bubble were calculated from the position plots. The results show a large velocity variation in all circuits, the ratio of the maximum velocity to the average velocity ranging from 3.5 for the X-bar to 4.8 for the chevron. Maximum vetocities in excess of that predicted on the basis of the critical velocity for dynamic conversion were observed.     

Aberration limits for annular Gaussian beams for optical storage

Annularly apodized beams have been suggested for use in optical storage because of their potential to go beyond the conventional spot size and depth-of-focus limits. One concern for such applications is the effects of small aberrations on beams in which the energy is concentrated in a small annular ring. We present calculations and experimental results that show that annular apodization of a Gaussian beam reduces the sensitivity to defocus as well as balanced spherical and coma aberrations. The sensitivity to astigmatism is increased by a small amount.     

Model-based far-field alignment algorithm for Gaussian beamlike single-mode optical devices

Single-mode device-to-fiber alignment automation is usually achieved with a classical mathematical optimization approach. We present a different approach, which is based on the identification of particular intrinsic characteristics of the coupled optical power and on estimating residual axial, transverse, and angular misalignments in the far field. Such a model-based approach is based on the physical nature of the optical coupling phenomenon and can replace or be complementary to already known automated alignment methods. An alignment algorithm is described and validated experimentally using two single-mode fibers as Gaussian beam emitter and receiver.     

Inorganic materials for optical data storage

Recyclable holographic (optical) storage in inorganic materials is nowadays possible due to the advent of laser. Various performance parameters of the state-of-the-art of optical storage are discussed in detail with reference to the well-established case of ferroelectric lithium niobate (LiNbO₃). Various physicochemical techniques are employed in understanding the microscopic mechanisms responsible for optical storage in LiNbO₃. A short summary of other inorganic materials capable of holographic storage is also presented.     

Optimization of the Gaussian beam flattening using a phase-plate

Abstract

We consider the conversion of a Gaussian beam into a flat-top profile by using a phase-plate which consists of a single-zone binary optic. The near- and far-field distributions are studied. We deduce the conditions required to produce super-Gaussian profiles of order 6 at the focal plane of a converging lens.     

Image oversampling for page-oriented optical data storage

Page-oriented data storage systems incorporate optical detector arrays [such as complementary metal-oxide semiconductor (CMOS) arrays] in order to read data images. For laboratory demonstrations the detector array is typically pixel matched to the data image [Opt. Lett. 22, 1509 (1997)]. This approach requires exceedingly high-performance optics and mechanics for the simultaneous alignment of each data-bearing pixel image to a detector element to be achieved. Systems intended for commercialization are designed with detector arrays that spatially sample the image at or above the Nyquist rate in order to read poorly aligned and distorted images [S. Redfield, Holographic Data Storage (Springer-Verlag, 2000), pp. 347-349]. However, for data page sizes exceeding a megapixel this approach becomes prohibitive in terms of detector bandwidth, size, power, cost, and processing requirements. We have instead developed a sub-Nyquist oversampling methodology that can recover arbitrarily aligned and distorted megapixel data page images with pixel-matched fidelity by using fewer than double the number of detector pixels. Features required for practicable implementation are described, including fiducials for alignment determination.     

Accelerating the annihilation of an optical vortex dipole in a Gaussian beam

When a Gaussian beam with two oppositely charged vortices propagates in free space, these two vortices will move around on the transverse beam plane. They may either move toward each other and annihilate each other spontaneously or survive all the way depending on the conditions. Here, we investigate how to force vortex dipoles to annihilate. We find that the background phase function created by two oppositely charged vortices during beam propagation can cause the vortices to move together and annihilate each other. The background phase function on a transverse plane just beyond the point where a dipole annihilated is continuous and retains the potential that forces a dipole to annihilate. We use this background phase function to accelerate the annihilation of vortex dipoles. Numerical results are provided to show the acceleration of dipole annihilation in a Gaussian beam, using such a background phase function.     

Experimental observation of fractional Fourier transform for a partially coherent optical beam with Gaussian statistics

We report the experimental observation of the fractional Fourier transform (FRT) for a partially coherent optical beam with Gaussian statistics [i.e., partially coherent Gaussian Schell-model (GSM) beam]. The intensity distribution (or beam width) and the modulus of the square of the spectral degree of coherence (or coherence width) of a partially coherent GSM beam in the FRT plane are measured, and the experimental results are analyzed and agree well with the theoretical results. The FRT optical system provides a convenient way to control the properties, e.g., the intensity distribution, beam width, spectral degree of coherence, and coherence width, of a partially coherent beam.     

Atomic force microscope cantilever calibration using a focused ion beam

A calibration method is presented for determining the spring constant of atomic force microscope (AFM) cantilevers, which is a modification of the established Cleveland added mass technique. A focused ion beam (FIB) is used to remove a well-defined volume from a cantilever with known density, substantially reducing the uncertainty usually present in the added mass method. The technique can be applied to any type of AFM cantilever; but for the lowest uncertainty it is best applied to silicon cantilevers with spring constants above 0.7?N?m(-1), where uncertainty is demonstrated to be typically between 7 and 10%. Despite the removal of mass from the cantilever, the calibration method presented does not impair the probes' ability to acquire data. The technique has been extensively tested in order to verify the underlying assumptions in the method. This method was compared to a number of other calibration methods and practical improvements to some of these techniques were developed, as well as important insights into the behavior of FIB modified cantilevers. These results will prove useful to research groups concerned with the application of microcantilevers to nanoscience, in particular for cases where maintaining pristine AFM tip condition is critical.     

Active media for optical data processing in optoelectronic devices

Peculiarities of color center production and their photostimulable recombination in doped alkali halide thin films have been analysed with regard to their availability as active highly sensitive luminescent storage media for fast optical data processing. It is concluded that the radiation defects in all the doped systems are spatially distributed in the near vicinity of the dopants. The influence of the surface is clearly pronounced in polycrystalline films. The escape of unrelaxed H-centers from the surface considerably changes the distribution of F- and dopant hole centers, forming an interacting F-center chain near the surface of grains. This is why temperature-independent F-center production and photostimulable recombination between distant pairs is observed in doped nanostructures. The main functional abilities of the active media are also discussed.     

Determining small angles of beam splitter rotation in optical vortex shearing interferometer

It is suggested to use a singular beam of unit topological charge in a scheme of vortex shearing interferometer intended for the observation of isoclinic fringes. In the interference pattern, the regions of fringe splitting determine the localization of wavefront dislocations and exhibit a shift that depends on the beam splitter rotation angel. Using the proposed method, it is possible to evaluate small angles of beam splitter rotation with an accuracy determined by the interference fringe width.     

Determining the density matrix of a molecular beam using a longitudinal matter wave interferometer

Abstract

Two separated oscillatory fields, if tuned to different frequencies, can generate or interrogate longitudinal momentum coherences in a beam of two-state particles. We demonstrate that use of differentially detuned separated oscillatory fields is an efficient method to determine the longitudinal density matrix of a particle beam.     

Three-dimensional optical data storage in a fluorescent dye-doped photopolymer

We propose a new, to our knowledge, monolithic multilayer optical storage medium in which data may be stored through the diffusional redistribution of fluorescent molecules within a polymer host. The active portion of the medium consists of a photopolymer doped with a fluorescent dye that is polymerized at the focal point of a high-numerical-aperture lens. We believe that as fluorescent molecules bond to the polymer matrix they become more highly concentrated in the polymerized regions, resulting in the modulated data pattern. Since data readout is based on detection of fluorescence rather than index modulation as in other photopolymer-based memories, the problems of media shrinkage and optical scatter are of less concern. An intensity threshold observed in the recording response of this material due to the presence of inhibitor molecules in the photopolymer allows for the three-dimensional confinement of recorded bits and therefore multilayer recording. The nonlinear recording characteristics of this material were investigated through a simple model of photopolymerization and diffusion and verified experimentally. Both single-layer and multilayer recordings were demonstrated.     

Nanometer scale polarimetry studies using a near-field scanning optical microscope

We describe a new technique that incorporates polarization modulation into near-field scanning optical microscopy (NSOM) for nanometer scale polarimetry studies. By using this technique, we can quantitatively measure the optical anisotropy of materials with both the high sensitivity of dynamic polarimetry and the high spatial resolution of NSOM. The magnitude and relative orientation of linear birefringence or linear dichroism are obtained simultaneously. To demonstrate the sensitivity and resolution of the microscope, we map out stress-induced birefringence associated with submicrometer defects at the fusion boundaries of SrTiO3 bicrystals. Features as small as 150 nm were imaged with a retardance sensitivity of approximately 3 x 10(-3) rad.     

Optical zooming interferometer for subnanometer positioning using an optical frequency comb

A high-precision positioning stage based on an optical zooming interferometer is proposed. Two external-cavity diode lasers, stabilized to a femtosecond optical frequency comb, are used as optical sources. The zooming principle is demonstrated, and the positioning resolution of 0.2 nm is achieved. The positioning accuracy was partly evaluated.