Measurement of laser-induced refractive index change of inverted ferroelectric domain LiNbO3

Optical nonlinearities of periodically poled LiNbO(3) crystals were investigated by the single beam Z-scan technique with a continuous wave (cw) laser beam at 532 nm. The nonlinear optical absorption coefficient and refractive index change are determined to be 8.1 x 10(-6) cm/W and 2.6 x 10(-4) at 0.5 MW/cm(2) light intensity, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the Z-scan results in congruent LiNbO(3). The nonlinearities in the periodically poled LiNbO(3) induced by 532 nm continuous waves are believed to be mainly due to the photorefractive effect.     

Scattering of electrons on thermal radiation photons in electron-positron storage rings

It is shown that Compton scattering on thermal radiation photons restricts the lifetime of high energy electron beams in storage rings to a level of 30 h. At a vacuum pressure of 10⁻¹⁰ Torr the probability that an electron is knocked out from the beam due to scattering on thermal photons exceeds the probability of bremsstrahlung on residual gas ( ) by one order of magnitude, i.e. this effect can cause a considerable background in detectors.     

Improvement of the beam lifetime by applying an rf electric kick field in the compact storage ring

The lifetime of the stored electron beam in the compact storage ring AURORA is governed by the Touchek effect. It has been shown that it is appreciably increased by applying a vertical rf kick field to the electron beam without giving harmful effect to the beam stability. Interferometric measurement of the radiation beam profile showed an increase in the beam size, indicating the reduction of the Touchek effect. Application of the field with increase in power has induced collective excitation of the betatron oscillation.     

Optical transition radiation proton beam profile monitor

For high energy and high intensity proton beams a new type of detector has been developed and tested in the CERN-SPS transfer lines. It uses the properties of transition radiation emitted, by the proton beam, when passing through a thin aluminium foil. Accurate transverse beam profiles can be obtained by means of this process. Compared to the classical secondary emission monitors the disturbance to the proton beam is reduced by an order of magnitude.     

Thermal efficiency of pulsed laser radiation increased by methods of multibeam acousto-optic diffraction

Bragg multibeam acousto-optic diffraction of pulsed laser radiation (with 150-ns pulse duration) has been studied under conditions of significant overlap between the neighboring beams. It is established that the initial beam with a Gaussian angular distribution of intensity can be transformed into diffracted radiation with a nearly rectangular profile of intensity provided that the laser pulse duration is much shorter than the period of interference beats in the overlapping regions. Using this circumstance, it is possible to increase the efficiency of high-power lasers in material processing (laser cutting, welding, engraving, etc.) with a threshold character of the radiation effect. This possibility was experimentally verified for a fiber laser operating at a 1.07 μm wavelength.     

On the Theory of a Non-linear Optical Resonator

The properties are considered of an optical resonator excited by an external light beam and filled with a non-linear (Raman or Mandel'stam-Brillouin active) medium for single-mode (exciting and the first Stokes) radiation components in the resonator. The form of the hysteresis of light intensity inside the resonator and of the intensity of the beam transmitted through the resonator for both the radiation components on the variation of the external beam intensity are investigated. Also, periodic pulsations of the radiation component intensities are discussed and the phase modulation of the components at the regimes in question is predicted, the conditions for these pulsations being derived. Conditions are also found under which the resonator amplifies the amplitude (phase) modulation of the external light beam and the properties of the regimes of the amplification are also discussed. The use of the resonator in question as the element of optical memory, a switching device, the generator of optical pulses and optical ‘transistor’ is proposed.     

Characterization of an Al-STJ-based X-ray detector with monochromatized synchrotron radiation

The characterization of an Al-STJ-based detector with Pb absorber was performed with monochromatized synchrotron radiation. Detector response was measured in the energy range from 3 to 10 keV. A small non-linearity of the signal pulse height was detected, probably due to the escape of recombination phonons from the detector. The non-linearity can be described by a second order polynomial function. Additionally, detector signals were recorded while an X-ray beam of 50 μm diameter was directed to several locations on and near the absorber. For a well-aligned beam, detector artefacts are of at least two orders of magnitude lower intensity than the absorber events.     

Effect of transient susceptibility on femtosecond pulse propagation in semiconductor quantum well waveguide

Ultra fast pulse evolution in a semiconductor quantum well structure (QWS) is theoretically analyzed. The polarization induced in the medium due to an incident Gaussian electromagnetic beam has been obtained using the semiconductor Bloch equations. The non-linear Schrödinger equation is used to analyze the effect of the induced polarization on the pulse. An interesting manifestation of the intensity dependence of the refractive index in non-linear media occurs through self-phase modulation (SPM), a phenomenon that leads to spectral broadening of the optical pulses. In doing the miniaturization of the device, we use semiconductor nanostructures in which the non-linearity is very large as compared to their bulk counterparts. Consequently, the phenomenon of SPM becomes significant at lower length scale leading to the limitations of the device. Numerical analysis was performed for a 150 fs Ti:sapphire laser radiation propagating along the transverse plane of a GaAs/AlGaAs QWS with realistic material parameters reveals asymmetric spectral broadening of the pulse due to SPM. The results agree qualitatively well with those available in the literature.     

Single Gaussian beam interaction with a Kerr microsphere: characteristics of the radiation force

We analyze the characteristics of the radiation force that is generated when a highly focused unpolarized Gaussian beam interacts with a nonabsorbing microsphere whose refractive index exhibits a first-order dependence on the beam intensity. The behavior of the force exerted on the sphere is analyzed as a function of beam power, axial distance, sphere radius, refractive-index difference between the sphere and the surrounding liquid, and wavelength. The force characteristics are compared with those of the radiation force that is generated when the electro-optic Kerr effect is absent. Our results show that a reversal in the net force direction is introduced when the Kerr effect becomes significant, which occurs at sufficiently high beam intensities.     

Radiation protection at synchrotron radiation facilities

A synchrotron radiation (SR) facility typically consists of an injector, a storage ring, and SR beamlines. The latter two features are unique to SR facilities, when compared to other types of accelerator facilities. The SR facilities have the characteristics of low injection beam power, but high stored beam power. The storage ring is generally above ground with people occupying the experimental floor around a normally thin concrete ring wall. This paper addresses the radiation issues, in particular the shielding design, associated with the storage ring and SR beamlines. Normal and abnormal beam losses for injection and stored beams, as well as typical storage ring operation, are described. Ring shielding design for photons and neutrons from beam losses in the ring is discussed. Radiation safety issues and shielding design for SR beamlines, considering gas bremsstrahlung and synchrotron radiation, are reviewed. Radiation source terms and the methodologies for shielding calculations are presented.     

Intensity, polarization, and phase information in optical disk systems

Digital information in optical data storage systems can be encoded in the intensity, in the polarization state, or in the phase of a carrier laser beam. Intensity modulation is achieved at the surface of the storage medium either through destructive interference from surface-relief features (e.g., CD or DVD pits) or through reflectivity variations (e.g., alteration of optical constants of phase-change media). Magneto-optical materials make use of the polar magneto-optical Kerr effect to produce polarization modulations of the focused beam reflected from the storage medium. Both surface-relief structures and material-property variations can create, at the exit pupil of the objective lens of the optical pickup, a phase modulation (this, in addition to any intensity or polarization modulation or both). Current optical data storage systems do not make use of this phase information, whose recovery could potentially increase the strength of the readout signal. We show how all three mechanisms can be exploited in a scanning optical microscope to reconstruct the recorded (or embedded) data patterns on various types of optical disk.     

Dependence of emittance degradation on beam angular momentum for charge exchange in solenoids

Beam emittance degradation associated with charge exchange in a solenoid depends not only upon the magnetic field and beam size at charge exchange but also upon the beam's angular momentum at that point. If the average beam angular momentum per particle is small compared to the corresponding rms value, this dependence disappears. If incident and final angular momenta for a cell have the same magnitude, there will be no emittance growth in that cell associated with charge transfer even though the sign of the angular momentum is reversed. Utilization of this effect to reduce emittance growth due to double charge exchange in two separated cells requires either a specially shaped magnetic field at the neutralizer cell or a beam transit time through the initial charge neutralization cell appreciably less than the cyclotron period of the beam in the cell. The length of the focusing region in a neutralizer cell can be increased by shaping its associated magnetic field. The consequent reduction in beam degradation for beams neutralized over that extended region is a function of the initial beam divergence and size separately and not solely a function of initial emittance.     

Experimental observation of self-transparency in an epoxybased polymer dispersed liquid crystal

Abstract

We report the observation of a self-switching effect from an opaque to a transparent state occurring at a critical incident intensity in a polymer dispersed liquid crystal. This self-transparency effect is analysed taking into account the beam profile variations of the light propagating inside such a medium. A clear self-confinement of the laser beam travelling in this composite material is also presented.     

Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.     

Fourier transform infrared synchrotron ellipsometry for studying the anisotropy of small organic samples

An experimental setup for polarization-dependent and spectroscopic ellipsometric measurements was developed that utilizes the brilliance of synchrotron infrared radiation at the electron storage ring at BESSY II for investigations of small samples and sample areas. During commissioning of the beamline and the experimental setup, a 1 mm2 piece of a well-characterized polyimide film was studied to show the benefits of Fourier transform infrared (FT-IR) synchrotron ellipsometry. The band shapes are interpreted with respect to the anisotropic distribution of transition dipole moments within the film. In comparison to a globar source, the signal intensity has been improved by more than one order of magnitude for this example.     

Back-action-induced Squeezed Light in a Detuned Quantum Non-demolition Scheme

Abstract

We describe the experimental observation and theoretical interpretation of a squeezing effect which occurs through the coupling of two light beams in a three-level atomic system. The origin of this effect can be attributed to the transfer of the intensity fluctuations of one beam to the phase fluctuations of the other one, followed by an optical feedback onto the intensity of the initial beam. The first step of the information transfer is similar to the one which occurs in a quantum non-demolition (QND) measurement of the intensity. The feedback effect is obtained through mixing of the phase and intensity quadratures, due to the detuning of the optical cavity which contains the nonlinear medium. Therefore the information obtained by the QND measurement is used to correct the intensity fluctuations of the signal beam by a build-in mechanism, which does not require any use of external electronics.     

Characterisation of a TES-Based X-ray Microcalorimeter in the Energy Range from 150 to 1800 eV Using an Adiabatic Demagnetisation Refrigerator

We characterised a TES-based X-ray microcalorimeter in an adiabatic demagnetisation refrigerator (ADR) using synchrotron radiation. The detector response and energy resolution was measured at the beam-line in the PTB radiometry laboratory at the electron storage ring BESSY II in the range from 200 to 1800 eV. We present and discuss the results of the energy resolution measurements as a function of energy, beam intensity and detector working point. The measured energy resolution ranges between 1.5 to 2.1 eV in the investigated energy range and is weakly dependent on the detector set point. A first analysis shows a count-rate capability, without considerable loss of performance, of about 500 counts per second.      

On the measurement of spatially-resolved energy characteristics of a high-power laser radiation

Behavior of a signal of the Rayleigh scattering of a laser radiation in air was studied depending on the parameters of an ultrasonic wave excited in the region of observation. It is shown that the presence of an ultrasonic wave in this region provides for a spatial resolution in the direction of observation with respect to the energy parameters of the laser radiation from the Rayleigh scattering measured at the sound frequency. The minimum intensity of laser radiation and the spatial resolution are estimated for a particular frequency and intensity of sound.     

Dynamics of the linearly polarized fundamental Gaussian light wave

A continuous planar array of dipoles that are oriented in a particular direction and have an amplitude distribution that is Gaussian in the paraxial limit is introduced as a source for the fundamental Gaussian light wave. The radiation intensity of the Gaussian light wave is determined and its characteristics are analyzed. The universal Gaussian beam factor is deduced and identified as the radiation intensity of the scalar Gaussian wave. The total radiated power, the mean center of the localized wave, and the beam widths of the intensity distribution are obtained. The ratio of the power in the Gaussian wave to that in the corresponding paraxial Gaussian beam is used as a measure of the quality of the paraxial beam approximation. A limiting factor for the power ratio is introduced as an indicator for the acceptability of the paraxial beam approximation. The cross section and the beam widths of the localized light wave are investigated in the large and small kw0 limits, where k is the wavenumber and w0 is the beam waist at the input plane. The beam width of the full Gaussian wave is found to be less than that of the corresponding paraxial Gaussian beam both for the scalar Gaussian wave and for the Gaussian light wave.     

On the luminescence properties of CaSO4:Ce

In conformal moving beam therapy with fast neutrons, the contributions to dose from the direct beam, scattered radiation and the gamma component vary with the position in the phantom. To determine this variation in radiation quality, microdosimetric measurements of energy deposition spectra were performed at different position in a therapy phantom. Fixed beam irradiation at different incidence angles showed strong changes in the lineal energy spectrum. An increase of slow protons (20 < y < 110 keV.micron-1) and a decrease of fast protons (2 < y < 20 keV.micron-1) was seen for irradiation outside the direct beam. During moving beam irradiation, different positions on the same isodose curves (55% or 35%) showed differences in YD of up to 5%. Variations in the quality parameter, R, determined by applying an empirical biological weighting function, were of similar magnitude. Thus, spatial variations in radiation quality should be taken into account in biological dose planning for moving beam neutron therapy.