Reflected Light Beam Research Articles

Optical bistability based on nonlinear oblique reflection of light beams from a screen with an aperture on its axis

It is shown that, in principle, optical bistability can be based on a nonlinear interaction of noncollinearly propagating beams when one of them is reflected from a plane screen with an aperture on its axis. The requirements to be satisfied by the interacting beams are discussed and estimates are obtained of the shortest response time of such an optically bistable system.

Solar Radiation Enhancement in a Lean-to Greenhouse by Use of Reflection

Abstract Computer simulations were conducted to investigate the effects of solar radiation enhancement on the cultivated area in a Chinese style lean-to greenhouse. The results showed that, under both direct and diffuse radiation, a more uniform distribution and increased amount of reflected radiation on the cultivated area could be obtained by installing a reflector [either an aluminized reflector or a polyvinylchloride (p.v.c) film sheet] from the ridge down to the ground [arrangement (b)] than by installing it on the interiors of the north wall and roof [arrangement (a)]. Moreover, to overcome the uneven distributions of the daily transmissivity of direct radiation when installing an aluminized reflector vertically from the ridge down to the ground, caused by the second reflection during winter months at 40°N and 45°N, an improved method was adopted. This method involves manipulation of the inclination angle of the aluminized reflector according to the solar altitude in such a way that the reflected light beam from the top of the reflector reaches the southern edge of the cultivated area at any time [arrangement (c)]. The analytical results indicated that not only the distribution uniformity, but also the total amount of reflected radiation on the cultivated area was marginally improved through this adjustment. When using the aluminized reflector under direct solar radiation, values of daily reflected radiation were 0·526 for arrangement (a), 0·691 for arrangement (b) and 0.712 for arrangement (c). Consequently, values of total solar radiation (incident+reflected) reaching the cultivated area were 1·276 for arrangement (a), 1·441 for arrangement (b) and 1·462 for arrangement (c). Similar results were obtained under diffuse radiation.

Interference in far-field radiation of two contra-propagating surface plasmon polaritons in the Kretchmann configuration

Work on experimental and theoretical study of interference of two contra-propagating surface plasmon polaritons is reported. In the experiments, the technique of attenuated total reflection in the Kretschmann configuration is used to launch the plasmon polariton on the surface of a thin silver film (∼500 Å in thickness), which covers the flat surface of a semicylindrical prism of optical glass. A mirror is used to send back the reflected light beam to the same area of the film. The reflected beam from the mirror launches another surface plasmon polariton in the direction opposite to the first surface plasmon polariton. Light beam from a He-Ne laser is used in the experiments. Noncoherent light from a monochromator is also used to help alignment. An interference pattern of the two surface plasmon polaritons is observed and is recorded with an optical microscope located in the air side near the film. The above device is also described theoretically with numerical calculations of interference fringe spacing.

レーザ拡散法による濃色ＰＺＴ基板微細クラックインプロセス自動検出技術

An automatic in-process detection system for narrow and short cracks in dark PZT plates used for piezoelectric parts has been developed. A crack in a dark PZT plate is difficult to detect because the diffuse reflectance of PZT is very low compared with that of an alumina plate. With this system, the contrast and SN ratio in the crack detection signal are improved. The former is improved by using a polarized beam splitter for separating the incident light beam from the reflected light beam. The latter is improved by illuminating the PZT plate with the optimum radiant flux of a laser and by setting the detection window at an optimum position. The 0.2 mm-long cracks with 1 μm and 3 μ m in width, are detected at 50% detection reliability and 100% detection reliability, respectively, using the laser scanning system developed for the in-process inspection.

ABCD matrix for reflection and refraction of Gaussian light beams at surfaces of hyperboloid of revolution and efficiency computation for laser diode to single-mode fiber coupling by way of a hyperbolic lens on the fiber tip

We report the formulation of an ABCD matrix for reflection and refraction of Gaussian light beams at the surfaces of the hyperboloid of revolution that separate media of different refractive indices. The analysis includes an arbitrary angle of incidence and is based on matching the optical phase at the interface. Finally, we deduce expressions for spot sizes and wave-front radii and use them to obtain the ABCD matrix. Based on the formulated ABCD matrix for refraction under paraxial approximation, we also report a simple theoretical investigation of the coupling efficiency of a laser diode to a single-mode fiber with a hyperbolic lens formed on its tip.

Contact time during impact of a spherical particle against a plane gas-liquid interface: experiment

The impact interaction of a solid sphere against an initially plane gas-liquid interface is experimentally studied with a new experimental principle. The interface is formed at the bottom of a capillary of about 8 mm inner diameter. The sphere impacts the interface inside the capillary. The new principle is based on video imaging of the grey levels of the gas-liquid interface using light beam reflection. The grey levels are recorded by a CCD high-speed video system. Collision time is determined as the time between the first two maxima of the grey levels and obtained by means of Fourier analysis. The dependence of collision time on the diameter and density of impacting particles is investigated and compared with the available theoretical models. The experimentally determined collision time is longer than the collision time predicted by the available theories. The reasons for this disagreement are discussed. The disagreement may be affected by the dependence of the restoring force on the radius of the plane gas-liquid interface.

Nonspecular reflection of general light beams at a dielectric interface

The reflection of light beams at a dielectric interface is studied from the moment method of light beam propagation. We obtain approximate analytical formulae for the geometrical nonspecular phenomena arising from the reflection of paraxial light beams of arbitrary spatial form, which apply to total and partial reflection, far and near the Brewster angle. New divergence modification and focal shift are predicted for the partial reflection of non-gaussian beams.

Laser diode to single-mode fibre excitation via hyperbolic lens on the fibre tip: Formulation of ABCD matrix and efficiency computation

From ray optics, we present a simple formulation of the ABCD matrix under paraxial approximation for reflection and refraction of light beams at a hyperbolic interface separating media of different refractive indices. Based on the formulated ABCD matrix for refraction by a hyperbolic interface, we report a simple theoretical investigation of the coupling efficiency of a laser diode to a single-mode fibre via a hyperbolic lens formed on its tip. Our results agree excellently with a recently published experimental result and also with the theoretical findings using quite involved phase distribution models. The analysis justifies the correctness of the prescription of the said ABCD matrix and also the simplicity of efficiency calculation, executable even by a pocket calculator. The technique will be useful in designing suitable microlenses employing laser micromachining technique.

Moment-method evaluation of the angular and lateral shifts of reflected light beams

From the moment theory of light beam propagation and reflection Fresnel formulae at a planar interface between two dielectric media, we find simple approximate analytical expressions for the angular and lateral shifts for partial and total reflection of ligh beams of finite transversal extent and arbitrary spatial form. A new lateral shift for partial reflection for asymmetric incident beams is found.

Reflection of a focused light beam in a kerr medium II. Numerical solution of the wave equation

The problem of studying the self-effect of a light beam in a nonlinear medium, and its scattering and reflection by the collapse region has been reduced to solving a system of high-order differential equations. This enabled us to use the Runge-Kutta method which improves considerably the accuracy in solving self-effect problems as compared with the conventional phase screen method. The self-effect and reflection of a light beam from the collapse region where the beam diameter decreases to the light wavelength λis investigated numerically. Calculations confirmed the main conclusions of the approximate solution of this problem which we obtained earlier in [1].

Demonstration of a recombined Fabry-Perot-Michelson interferometer with suspended mirrors

We describe preliminary experimental results concerning the operation of a 3 m arm-length Michelson interferometer with two Fabry-Perot cavities whose mirrors and beam splitter are suspended independently by wires. The reflected light beams from the two Fabry-Perot cavities are recombined to obtain interference at a photo-detector; this scheme is necessary for future power-recycled laser interferometers used to detect gravitational waves. The fundamental properties of the interferometer are presented, including the power spectral density of the displacement noise.

Variable optical delay line based on a birefringent planar optical platform

A variable optical delay line is proposed for accurately adjusting optical signal timing in photonic systems. This delay line is based on a birefringent planar optical platform characterized by the multiple reflection of light beams. It consists of a birefringent plate, lambda/4 plates, mirrors, and a liquid-crystal layer. It can select an arbitrary delay from a set of discrete delays precisely determined by the thickness of the birefringent plate. A feasibility study confirms seven-step delay line operation with a 240-ps unit delay.

A Fiber Optic Non- Contact Accelerometer

A novel non-contact fiber optic accelerometer is presented. Two laser beams that have passed through two different lengths of feed fibers are launched to the same moving target. The frequency of each beam is Doppler shifted by movement of the target. The frequency shift of the laser beam corresponds to the velocity of the target at the time of launch. The difference in launching time due to the difference in feed fiber lengths samples the velocities of the target at times spaced by the differential arrival times of the laser beams. Two return passes of the reflected light are also made different so that the light passed through the shorter feed fiber is steered to the longer return fiber by means of a combination of A/4 plate and polarization beam splitter (PBS). This arrangement of equalizing the total paths relieved a stringent requirement of the coherency of the laser. Two reflected light beams are mixed and the beat frequency corresponds to the difference in the Doppler shift frequency at two different times of arrival of the launcher. An accelerometer based upon this principle was constructed and its performance was examined using a sinusoidally vibrating hydrophone as a target. Features of such an accelerometer are reduction in the coherency requirements of the light source and simpler amplification of the signal using heterodyne detection.

Interference wedge properties relevant to laser applications: transmission and reflection of restricted light beams

The optical properties of the interference wedge are analysed for the case of restricted laser beam illumination. By further development of Brossel's method, equations describing this case are derived and used to calculate the reflected and transmitted beam profiles for typical intracavity laser beam diameters (0.2–0.6 mm) for Gaussian and uniform intensity distributions. In particular, the experimentally observed formation of bright fringes outside the beam impact area at resonant wavelengths is explained. some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.

Optical measurement of crack propagation with high resolution

A new optical method is established to measure the crack length and its velocity in transparent crystals by utilizing the total reflection of light beam at the cleavage crack plane. The optical system is constructed by using a laser, a PIN photodiode sensor, and a wave memory. With the apparatus the crack propagation velocity can be measured at any desired position inside the specimen with a time resolution of less than 1 μs. The measurement on a cleavage crack in NaCl reveals that the maximum speed of the crack is about 800 m/s and the fluctuation of the velocity occurs prior to the arrest.

Determination of potential of zero charge of a mercury electrode by dispersion of reflected light, dependent on curvature of a drop

A novel method for the determination of the potentials of zero charge of Hg or liquid amalgams in various solutions in described. It is based on the effect of potential on the surface tension of Hg, giving rise to changes of curvature of a Hg drop. The changes of curvature are transduced to a varying light-intensity ( LI) signal through reflection of a collimated thin laser beam, incident on the top of the drop. Dispersion of the intensity of the divergent reflected light beam is measured by a photo-diode and is at a maximum at the potential of zero charge where the Hg drop has the shortest focal length as a convex mirror. The observed LI is then at a minimum. Kinetic effects associated with slowness of adsorption/desorption of ions may also be observed in cases where specific adsorption of anions arises. The minimum is located by plotting, vs. potential, the reciprocal derivative of LI with respect to potential or by employing the method of “rectilinear diameters”. The reflection method is applicable to solutions of any concentration and also to non-aqueous media. Examples are shown for aqueous alkali halide solutions and for one non-aqueous solution.

Optical bistability with the waveguide mode: the case of a finite-width incident beam

We develop an approximate analytical theory for the reflection of a finite-width square-wave light beam at a nonlinear interface and make use of the results to assess the effect of the finiteness of the incident beam on the bistability of the signal reflected from a triple boundary interface under conditions for excitation of a waveguide mode. The nonlinearity of the interface is assumed to result from a substrate medium that has a Kerr-type quadratic dependence on the local electric-field amplitude. Our results indicate that the finiteness of the width of the incident beam substantially reduces the magnitude of the reflectance jump at the bistable switching point in comparison with that predicted by an exact plane-wave theory. Nevertheless, we conclude that a bistable reflectivity should still exist for the geometry that we consider at the switching intensity predicted by the plane-wave theory.

Surface profile measurement with a scanning differential ac interferometer

In scanning systems for surface profile measurement, e.g., stylus systems, the profile of a surface is generally determined by measuring the distance of the surface relative to a reference plane. This can be either a plane defined by a moving stage under a rigid stylus or a plane defined by a moving stylus if a fixed stage is used. In both cases, the measurement precision is limited by the straightness of a linear motion. This paper presents a new interferometric profile measurement technique based on using a rigid differential interferometer probing the test object which is moved by a stage. Information on the surface profile is obtained by scanning the surface with two laser spots simultaneously and measuring the optical path difference between the reflected light beams. This makes the profile measurement largely insensitive to flatness errors of the mechanical stage and enables extremely precise measurements. Data processing is done digitally using a storage scope and a microprocessor. The suitability of this method for measuring the profiles of magnetic sliders and SIMS sputter craters has been investigated. The experimental work includes long- and short-term repeatability tests and an extensive investigation of the temperature dependent behavior of the measuring instrument.

Deflection of Light by Ferroelastic Domains in Gd2(MoO4)3 and Bi4Ti3O12 Crystals

The relation between angles of incidence and deflection caused by the refraction and reflection of light beam at the ferroelastic domain walls in Gd 2 (MoO 4 ) 3 , Bi 4 Ti 3 O 12 and Rochelle salt crystals has been treated on the basis of crystal optics. Numerical analysis of the relation has been carried out for incident angles from 0° to 90°. At the incident angle of 0°, the deflection angles obtained by the analysis are 2.25° for the c plate of Gd 2 (MoO 4 ) 3 , 14.6° for the b plate of Bi 4 Ti 3 O 12 and 4.43° for the a plate of Rochelle salt. The experimental results with a He-Ne laser for these crystals are in satisfactory agreement with the calculated ones. The intensity ratio of the deflected beam to the direct beam is in the order of 10 -2 for Gd 2 (MoO 4 ) 3 and 10 -3 for Rochelle salt.

Stabilization of diode laser output by beveled-end fiber coupling

A new laser-to-fiber coupling scheme, which eliminates unstable phenomena caused by optical feedback, is proposed and demonstrated experimentally. This coupling module contains a packaged diode laser, two lenses, and a beveled-end fiber. Depending on the beveled angle, the reflected light beam from the fiber will be displaced with respect to the emitted light beam at the laser facet, and stabilization of laser output power and spectrum are achieved.