Beams Of Different Wavelengths Research Articles

TeO2 single-crystal acoustooptic 2×2 switch for light beams of different wavelengths

The principles of acoustooptic switching of two light beams of different wavelengths by means of an acoustooptic interaction with two acoustic waves are examined. A version in which the acoustic waves form parallelograms and a version with strictly orthogonal propagation are considered. The latter version is the more attractive one when a TeO2 single crystal is used as the acoustooptic cell. Experiments on the switching of two-color Ar laser radiation with wavelengths λ1=0.5145 and λ2=0.488 µm are carried out and demonstrate a high switching efficiency. On the whole, the experiment confirms the basic conclusions of the theory.

Steady-state photorefractive soliton-induced Y-junction waveguides and high-order dark spatial solitons

We report the experimental observation o steady-state photorefractive Y junctions and sequences of high-order dark photorefractive screening solitons in a biased bulk strontium barium niobate crystal. The parameters that characterize the properties of the high-order dark screening solitons are measured and compared with the theoretical prediction for the fundamental dark screening soliton. The high-order dark solitons induce stable waveguides in one transverse dimension that can guide other, possibly very intense, beams of different wavelengths.

Determination of interface recombination velocities and carrier lifetimes in SOI materials by a contactless optical modulation technique

A novel contactless dual-beam optical modulation (DBOM) technique has been employed for determining the interface recombination velocities and substrate carrier lifetimes in a SIMOX (Separation by IMplantation of OXygen) wafer. The DBOM method utilizes the optical modulation of the transmitted light intensity of an infrared (i.r.) probe beam ( hv < E g) modulated by a CW visible laser pump beam ( hv > E g) of different wavelengths (e.g., λ = 442 and 632.8 nm) via free-carrier absorption in the SIMOX wafer. The interface and bulk recombination velocities were determined by using pump beams of different wavelengths and incident angles. A theoretical model for the DBOM technique has been developed for extracting the interface recombination velocities and substrate lifetimes in the SIMOX wafers. The front-interface [Si film/buried oxide layer (BOX) interface] and back-interface (BOX/Si substrate interface) recombination velocities as well as the substrate carrier lifetimes were determined using this new technique. Mappings of the front- and back-interface recombination velocities and the substrate carrier lifetimes for several SIMOX wafers with different Si film thicknesses and oxygen implantation processes have been carried out.

Magneto-optical position-resolving sensor for displacement measurements between light beams

The dispersion of the refractive index of the atmosphere leads to small angles (δβ ≈ 1 μrad) between light beams of different wavelengths (e.g., red and green) and therefore the images of these beams in the focal plane of a telescope are displaced by a few micrometres. According to this fact, geodetical refraction measurements can be accomplished by a position-resolving sensor. The magneto-optical transversal Kerr effect of a 40 nm thin iron film is used to modulate the light beams up to 100 kHz. Separating the beams by a colour-sensitive beamsplitter, the displacement between the two focal points is measured by the time difference of the corresponding photodiode signals. The relation between the time and a locally defined magnetization reversal of the film is achieved by a ferrite C—yoke with gradient pole shoes and the rectangular hysteresis of the iron film. Simulating the conditions of refraction measurements in the atmosphere at a total light power of 5 μW on the front end of the telescope (focal length 1.5 m), a resolution of 35 nm is achieved, which corresponds to an angular resolution for δβ of 23 nrad.

Universal Particle Detector Experiment

The Universal Particle Detector Experiment (UPDE), which consists of two parallel planes of diode laser beams of different wavelengths and a large surface MOS impact detector, will be used to test a novel technology for real-time monitoring of particles impacting a spacecraft surface with high resolution of time, position, direction, and velocity. The particle database will in turn be used to validate contamination and orbital debris models to predict optimal configurations of future space sensors and other sensitive surfaces. Besides measuring particles fluxes, the UPDE will also be capable of determining the velocity and size distributions of the ambient and self-induced particles around the spacecraft. With two different color diode lasers, particulate composition will also be determined based on laboratory calibration with different materials. Secondary particles dislodged from the top aluminum surface of the MOS detector will also be measured to determine the kinetic energy losses during energetic orbital debris impacts. The velocity range of this instrument is 0.1 m/sec to 14 km/sec, while its size sensitivity is from 0.2 μm to millimeter-sized particles. The in-space particulate measurements in space of the kind proposed here will be the first simultaneous multipurpose particulate experiment to include velocities from very slow to hypervelocities, sizes from submicron to pellet-sized diameters, chemical analysis of the particulate composition, and the kinetic energy loss after energetic impact of space debris.

Simultaneous confocal recording of multiple fluorescent labels with improved channel separation.

Confocal microscopes are often used to study specimens labelled with fluorophores. A commonly used method for simultaneous recording of the distribution of multiple fluorophores is to divide the fluorescent light emitted by the specimen into different wavelength regions using dichroic and bandpass filters. These different wavelength regions are then distributed to multiple detectors. However, the broad and overlapping spectra of commonly used fluorophores often result in considerable crosstalk between channels. A new technique, intensity-modulated multiple-beam scanning (IMS) microfluorometry, can be used to reduce this cross-talk substantially. The IMS technique is implemented with two laser beams of different wavelengths, intensity-modulated at different frequencies, which illuminate the specimen simultaneously. The two laser wavelengths predominantly excite one fluorophore each. Fluorescent light from the specimen is divided into two wavelength regions (red and green) which are detected by two photomultiplier tubes. The output signals from the photomultiplier tubes are connected to lock-in amplifiers. The effect of using modulated laser beams, in combination with lock-in amplifiers, is strongly to reduce cross-talk between the channels. The performance of the IMS technique using various types of specimen is compared with the results obtained using the conventional multi-detector method.

Developments of the amplified stimulated emission technique for spatially resolved species detection in flames

It is demonstrated that the amplified stimulated emission technique can be applied for spatially resolved detection of flame species requiring a two-photon excitation process. The approach utilizes two laser beams of different wavelengths produced by a dual wavelength package in the dye laser. By wavelength separation through the use of two different doubling crystals fulfilling the phase-matching condition for only one beam at a time, followed by crossing the beams in the flame, a substantial increase in spatial resolution is achieved. The technique is demonstrated on ammonia in a jet and on carbon atoms in a welding torch flame.

Multi-colour-pumped oscillator in photorefractive BaTiO 3

A photorefractive multi-colour-pumped oscillator is described. Oscillation beams, generated by three input beams of different wavelengths, show the effect of competition resulting in their different build-up and behaviour. A theoretical model, based on two sets of coupled differential equations gives good agreement with experimental data.

Magneto-optical high resolution measurement of small displacements between light beams of different color

The magneto-optical Kerr-effect of a 40 nm thin iron film is used to modulate light beams of different color (e.g., red and green) up to 100 kHz. Yielding a resolution of 35 nm at a total light power of 5 /spl mu/W, the displacement between the two focal points of these beams is measured by the time difference of the corresponding photo diode signals. The relation between the time and a locally defined magnetization reversal of the film is achieved by a ferrite C-yoke with gradient pole shoes and the rectangular hysteresis of the iron film. Besides various optical measurement applications, the method is foremost useful for studying the atmospheric refraction, where the dispersion of the refractive index leads to small angles (/spl ap/1 /spl mu/rad) between light beams of different wavelengths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Position dependence of the transient response of a position-sensitive detector under periodic pulsed light modulation

A model based on sinusoidal steady-state analysis is developed for the position-sensitive detector (PSD), which is approximated as a distributed RC transmission line. This model is used to study the output response of the lateral effect PSD (i) when only one pulse-modulated light beam is incident and (ii) when two light beams of different wavelengths, with one beam modulated at a frequency f and the other beam modulated at a frequency 2f, are incident at the same time. The simulation shows, and experiments confirm, that the transient response of the PSD consists of a position-dependent dead time (time for the output current to sense the change in the induced photocurrent) and a position-independent exponential rise decay time. For the application of resolving the positions of two or more pulsed-modulated light spots, it is shown that there is a position-dependent upper limit on the usable modulation frequency. With the per-unit-length values chosen for the sheet resistance as R=315 Omega /mm and the junction capacitance as C=330 pF/mm, the modulation frequency limit is determined to be 20 kHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Shared aperture for two beams of different wavelength using reflective phase gratings and the Talbot effect

A shared aperture system for two laser beams with different wavelengths and composed entirely of reflective phase gratings is described. Beams that share an aperture are collinear, and they have the same transverse phase profile across the aperture as their respective sources. Using the Talbot effect that is observed in Fresnel diffraction from periodic objects, we preserve the phase of the beams, and we maximize the efficiency of the system. An experimental Talbot shared aperture system using He-Ne and He-Cd beams has an efficiency of 88.1% for the He-Ne beam and 70.3% for the He-Cd beam. These measured efficiencies agree well with theoretical predictions and computer simulations.

Analysis and compensation of thermal effects in laser-assisted scanning tunneling microscopy

As an indispensable step towards detection of selective, resonant light absorption in laser-assisted STM, we analyzed the thermal expansion produced by laser irradiation of the tunneling junction. The expansion as a function of the modulation frequency of the light power could be related to the specific heat and thermal conductivity of the materials involved. A scheme is presented, aiming for detection of small tunneling current changes induced by resonant optical excitation of an adsorbate. It is based on the idea of irradiating the tunneling gap with two laser beams of different wavelengths—only one being in resonance with the adsorbate—and suppressing the thermal contribution to the tunneling current by an amplitude modulation of both beams with a 180° phase shift.

Method for planar measurement of temperature in compressible flow using two-line laser-induced iodine fluorescence

A method for planar measurement of temperature in a compressible flow by means of two-line laser-induced iodine fluorescence is proposed. Temperature is determined from the ratio of the intensities of fluorescence, which are obtained by irradiation of two laser beams of different wavelength. Use of a high-sensitivity vidicon camera permits multiple-point measurements of temperature in the flow field. This method is applied to a supersonic free jet. It is found that the results obtained by P(16)/R(18) (514.720 nm) and P(26)/R(28) (514.942 nm) absorption lines in the transition of B(3)II(ou)+ (nu' = 43) ? X(1)sigma(g)+ (nu'' = 0) can predict temperature below 300 K with an accuracy of +/-5K.

A108 PLIF法による希薄気体流の二次元温度場の可視化

A method for measurement of two-dimensional temperature field in rarefied gas flow by two-line laser induced fluorescence is proposed. Temperature is determined from the ratio of the intensities of fluorescence, which are obtained by irradiation of two laser beams of different wave length. Use of a laser sheet and a high-sensitivity vidicon camera allows multiple-point measurements of temperature in the flow field. Effectiveness of this method is verified by its application to the determination of the temperature distribution of a supersonic free jet. It is found that the results obtained by P(16)/R(18) [514.720 nm] and P(26)/R(28) [514.942 nm] absorption lines in the transition of B3∏o+u(v'=43)←X1Σ+ 8(V"=0) can predict temper-ature below 300 K with reasonable accuracy.

Diffraction of He and Ne and selective adsorption of He on Rh(110).

Diffraction studies on clean Rh(110) have been performed with room-temperature and low-temperature He and Ne beams. The corrugation amplitude perpendicular to the close-packed rows as observed with He is z(01)=0.15 A\r{}. Regarding analogous data for Ni, Cu, Pd, and Ag, this value fits well into the now clearly discernible trend that z(01) increases strongly with increasing lattice constant. The corrugation amplitude along the close-packed rows, z(10), on the other hand, does not show such systematic behavior. Compared to the other metals, the value for Rh, z(10)=0.065 A\r{}, is exceptionally large. z(01) measured with Ne is about twice as large as observed with He in accord with previous observations on other metals. Selective adsorption structures of He on Rh (110) were traced with low-temperature beams of different wavelengths and allowed the determination of four bound-state levels. The measured energies were fitted with different analytical potential forms and yield a potential-well depth of \ensuremath{\sim}8.2 meV.

Optical measurement of the inner scale of turbulence

Presents a method for the determination of the path-averaged value of the inner scale of atmospheric turbulence, l0, using an optical scintillometric method. The proposed method involves the measurement of the bichromatic correlation of two laser beams of different wavelengths propagating in overlapping paths. Results obtained using this technique are compared with the ratio of the log-amplitude variances of the two laser beams and with l0 values derived from vertical wind velocity fluctuation measurements. The results of the correlation method agree well with theory based upon Hill's refractive index spectrum. Results obtained by the ratio of variances match those obtained by the correlation technique after correction for the refractive index dispersion due to humidity fluctuations. These two methods can be used jointly for the simultaneous determination of l0, CT2 and CQ2.

Photoconductive Enhancement of Degenerate Four-wave Mixing Reflectivity in BSO

Abstract A method of enhancing the degenerate four-wave mixing (DFWM) conjugate reflectivity in photorefractive BSO is described, which uses an auxiliary beam of different wavelength to modify the local conductivity inside the crystal. With an applied external electric field of 6 kV cm−1, and small diameter DFWM beams, the auxiliary enhancing beam is used to increase local conductivity and hence drop essentially the entire voltage across the small DFWM region producing local fields of ⋍30 kV cm−1. A simple model is derived for three separate experimental configurations, and the predictions are compared with experimental results using yellow and blue beams for DFWM and enhancing beams respectively.

On obtaining well defined transverse modes and selective line tuning of a long CW CO2 laser

It is found that a long conventional CW CO2 laser cannot be tuned selectively because of the multidirectional modes formed through reflections at grazing angles from the inner walls of the discharge tubes. This problem has been overcome by inserting a number of properly designed mode-selecting apertures right into the discharge tubes and selective tuning over more than 150 rotational lines in both P and R branches of three vibrational bands (9.6, 10.6 and 11.2 mu m) has been achieved. The rotational lines of higher J-values that have a low gain tend to lase in the TEM10 mode. In the R branch two consecutive lines are observed to lase simultaneously when the angular width of the active medium subtended at the grating allows the existence of two physically tilted beams of different wavelengths dispersed by the grating used. The output power distribution over various lines almost follows that of the gain. The optimum design parameters of a long CW CO2 laser for tuning are obtained.

A molecular beam study of electronic to electronic, vibrational, and rotational energy transfer in the collision of two step laser excited sodium with N2

The quenching of excited Na* (4d,5s,4p,4s) by N2 has been studied in a crossed atomic and molecular beam apparatus at thermal collision energies. The sodium atoms are excited by two laser beams of different wavelengths to either the 42D5/2 or 52S1/2 state, via the intermediate 32P3/2 state. For both excitation schemes optical relaxation processes lead to a population in the 42P3/2 and 42S1/2 states of several percent. The relative densities of the excited states have been calculated from rate equations using stationary conditions. The measured energy transfer spectra show high scattering intensities at low kinetic energies together with some structure at medium energies. This structure can be partially disentangled using the results of the previously studied Na*(32P3/2)+N2 quenching process. The main conclusion is that collisional deexcitation to the Na(3s) ground state is negligible, whereas among the higher levels the collisional energy transfer cross sections are between 0.5 and 7.5 times the magnitude of the 3p–3s quenching cross section and they are strongly forward peaked in the same way. Relative values for the differential quenching cross sections are reported.

Multistation multiparameter flow cytometry: a critical review and rationale.

The capacity for fluorescence excitation by beams of different wavelengths at separate points along the sample stream, and the capacity for computer analysis of multiparameter data thus obtained, are now available in flow cytometer/sorter systems from commercial producers. It is now readily apparent to most experienced users of flow cytometers that such multiparameter analysis offers the most convenient solution to the problem of characterizing subpopulations of cells within a mixed population. The use of multiple beams facilitates resolution of fluorescence signals from several probes within or upon a single cell and widens the range of analytical alternatives available to experimenters. This critical review discusses the history of the instrumentation, the parameters now measurable and the probes used for their measurement, and the methods for data analysis. Required sensitivity and precision are discussed, leading to the conclusion that many of the advantages of multistation, multiparameter flow cytometry can be made available in less complex and less costly instruments using less powerful sources and less elaborate computer hardware than are presently incorporated in commercial apparatus.