Total Incident Intensity Research Articles

Double Phase Conjugate Mirror with Sb-Doped Sn2P2S6 Crystal for Different Incident Angles, Crystal Thickness, Total Incident Intensity and Polarization

We developed photorefractive Sb-doped Sn2P2S6 samples of different crystal thickness to investigate the properties of the media for double phase conjugation. The Sn2P2S6:Sb crystals have high coupling coefficient of 20 cm−1, and show fast response time of 1.3 ms at total incident intensity of 0.3 W/cm2. The maximum phase conjugate reflectivity of 32% was observed with a 4 mm thickness sample. To investigate the characteristics of Sn2P2S6:Sb for double phase conjugation, on the basis of the coupled wave equations, we showed the dependence of phase conjugate reflectivity on incident angle, crystal thickness, total incident intensity and polarization. From these results, the optimum incident condition was clarified for obtaining the highest phase conjugate reflectivity.

Simulation of silicon PIN photodiodes for use in space-radiation environments

A computer program for the simulation of semiconductor devices has been developed and applied to the analysis of radiation effects on Si PIN photodiodes. The study has allowed the authors to propose useful analytical models related to such optical and electrical device parameters as peak spectral response and dark current. Peak spectral response has shown a marked dependence on device layers dimensions. Dark current has demonstrated linear increase with intrinsic layer length and proton-radiation fluence. But the most important obtained result has been the determination of a particular set of semiconductor P-, I- and N-layer thicknesses, for given values of total device length and incident light intensity, that minimize radiation effects during photodiode operation in space environments up to high particle fluences.

Hologram multiplexing in acrylamide hydrophilic photopolymers

Unslanted diffraction gratings are recorded in a 900μm thick acrylamide photopolymer by means of peristrophic multiplexing. A solid state Nd:YAG (λ=532nm) laser is used as the recording beam, with a total incident intensity of 5mW/cm2, and a He–Ne laser as the reconstruction beam. The dye concentration in the photopolymer is optimized so that it does not limit the dynamic range. Nine holograms are recorded using constant exposure time scheduling and variable exposure time scheduling. From the results obtained it may be deduced that optimization of the dye allows us to work in the linear response region of the photopolymer and at the same time obtain high values of diffraction efficiency for each hologram. An exponential increase in exposure time as the number of holograms increases enables the values of diffraction efficiency to be homogenized with regard to the case of constant exposure scheduling. In this way, better use is made of the dynamic range of acrylamide hydrophilic photopolymer.

Influence of intensity on the steady and transient state space-charge fields in photorefractive polymers

We have proven theoretically that there are sublinear, linear and superlinear relations between the response rates and total incident intensity for different cases of traps in photorefractive polymer materials. These relations were observed in inorganic photorefractive crystals many years ago. Also, the steady-state space-charge field is a function of the total incident intensity, which has also been found in inorganic photorefractive crystals. We have measured the relations of the steady-state diffraction efficiency and the response rate with respect to the total incident intensity in the photorefractive composite consisting of the polymer (N-vinylcarbazole) (PVK) doped with 4,4'-n-pentylcyanobiphenyl (5CB) and C60. The results obtained show that the composite belongs to the case of low trap density.

Forced-oscillator model of a photorefractive space-charge field that is due to carrier population variation

Without using the usual assumption of free-carrier quasi-static distribution, we derive a forced-oscillation equation with damping to describe the buildup of a fundamental harmonic space-charge field in inorganic photorefractive (PR) crystals. Thus the PR holographic records of static gratings and dynamic gratings can be understood in terms of the usual vibration theories. The solution of the equation is biexponential and encompasses two time constants that had been observed in some PR materials. The ratio of the two time constants is calculated as a function of experimental parameters, such as the total incident intensity and the applied electric field, to prove the applicability of our model. Results show that the difference between the two time constants may be so small that neither of the constants can be neglected. Additionally, the resonance frequencies obtained from the two models for the moving grating are compared, and a figure of merit Q is defined to describe the resonance properties. All the results show that our model can be applied to general cases.

Theory of space-charge field with a moving fringe in photorefractive polymers

Resonance of space-charge field can occur in photorefractive polymers through a moving fringe and can be described by a forced oscillation equation with damping. The resonance frequency and the magnitudes of both the amplitude and the imaginary part of the space-charge field at the resonance frequency are functions of three experimental parameters: total incident intensity, applied electric field, and grating wave vector. Thus, the diffraction efficiency of grating and the gain coefficient of two-wave mixing are dependent on the three experimental parameters. Our theory can also be applied to inorganic photorefractive crystals.

Kinetics of the formation of space-charge field in photorefractive polymers

We derive a kinetic differential equation for the formation of space-charge field (SCF) in photorefractive polymers and give its general solution, which is based on Schildkraut’s work. It is found that SCF consists of two exponential decay waves and there are two decay factors corresponding to two response time constants of SCF. Changing the parameters in the solution, we can understand the formation of SCF for different cases. In this article, we discuss a case of no traps and find that both static and transient actions of SCF are determined by the grating wave vector k and total incident intensity Ii.

Intensity dependence of phase shift in photorefractive gratings

The phase shift of the photorefractive grating against the interference intensity pattern in the two-wave mixing with Bi12SiO20 crystal has been measured as a function of the total intensity of the reference and signal beam when the intensity ratio was always constant. The phase shift departures from 90° as the total intensity increases. According to the change of the phase shift, two-wave mixing gain decrease as a function of the total incident intensity.

Phase shift between index and intensity patterns in photorefractive two-wave mixing experiments in InP:Fe

The phase shift between the intensity pattern and the index pattern in two-wave mixing experiments has been determined from measured values of photorefractive two-wave mixing gain and diffraction efficiency in a bulk InP:Fe crystal as a function of the total incident intensity. Remarkably, the phase shift varies from 0 to 180° with a value of 90° at the intensity for which the two-wave mixing gain peaks. Comparison between theory and experiment yields values for sample Fe 2+ and Fe 3+ concentrations.

INTENSITY DEPENDENT PICOSECOND LIGHT PULSE SHAPING IN PHOTOREFRACTIVE CRYSTAL BY TWO WAVE COUPLING

Pulse shaping by two wave coupling in Ce doped KNSBN crystal is realized with a frequency-doubled CW modelocked Nd:YAG laser whose output pulsewidth is about 55ps. When the total incident intensity is higher than 10W/cm2, the shaping effect becomes more and more prominent with increasing incident intensity. The experimental results show good quantitative agreement with theory.

Energy transfer in Sr 0.56Ba 0.44Nb 2O 6:Ce AT 633 nm

A steady-state solution for two-wave mixing equations in SBN:Ce is presented in which the absorption of light and the thermal generation of the carriers are taken into account. The energy transfer between the two writing beams in SBN:Ce are analyzed as a function of the following parameters: total incident intensity, incident beams ratio and spatial frequency. The experimental results show that an exponential gain coefficient Γ ≈ 22 cm -1 is reached for optimized writing conditions.

High-Speed Surface Roughness Measurement

A prototype apparatus is described that performs a real-time optical measurement of surface roughness in the 2 to 20 microinch AA range, typical of high-quality grinding, honing, and lapping. Ground metal manufactured parts, with surface roughness in the stated range, are illuminated with a 3.39 micron helium-neon laser. The scattering pattern from the surface is scanned across a linear array of lead selenide detectors. Analog and digital electronics control the scanning and measure the intensity incident on each detector. The electronics computes both reflected (specular) and total incident intensity. These two values are used to compute the surface roughness. The system completes a scan and the electronics computes surface roughness in 20 milliseconds. The fast measurement time allows a large area to be scanned. The results demonstrate the feasibility of using the apparatus for online inspection.

Transient energy transfer during hologram formation in LiNbO 3 in external electric field

Volume phase hologram recording in pure LiNbO 3 crystals with applied electric field E ≈ 5 kV/cm is accompanied by considerable intensity redistribution of the writing beams by transient energy transfer. Practically the whole intensity of the donor beam may be transferred into the weak acceptor beam with initial intensity 3% from total incident intensity. This effect originates from transient phase mismatch of the recorded phase grating and fringe pattern in the applied electric field when the interacting beams have different intensities.

Some Calculations of the Thickness Distribution of Films Deposited from Large Area Sputtering Sources

The distributions of intensity incident upon parallel and perpendicular receiver elements are derived for a uniform, cosine-emitting, circular plane source. The exact expressions representing these distributions have been computer-evaluated and machine-plotted using normalized parameters; these plots are presented. In addition plots are given of the contributions to the total incident intensity on centered receiver elements from circular ring and linear strip elements of the source. The derivation proceeds with the point of view that the source is a sputtering or evaporation surface; it assumes that no molecular scattering occurs during transit and that the sticking coefficient on the receiver is unity. It is found that, for adjacent perpendicular and parallel receiver elements located within the projection of the disk source, the intensity incident upon the perpendicular element is significantly less than that incident upon the parallel element.