Beam combiner

The different studies are mainly reported on the OBLIN site (NASA). The main goal is to simplify and integrate all the functions to be achieved in the beam combiner by using integrated optics and optical fibre components. Consequently, the compactness, the stability and the reliability are significantly improved. Figure 15 illustrates the simplification of the experimental setup. 

Lastly, BNCT is used today in combination with fast neutron therapy in some centers such as Seattle, Essen, and Orleans. Boron is incorporated in the tumor cells it captures thermal neutrons produced in the body by the fast neutron beam. Combination of BNCT and external photon beam therapy has also been suggested [51]. 

Equations (2.75) and (2.76) represent two extremes. The former applies to a perfectly monochromatic beam incident on a perfectly parallel, smooth slab (although perfection in this sense is not absolute but lies within certain tolerance limits). On the other hand, the latter equation is appropriate to what might be called the perfectly imperfect case a slab-beam combination that has been carefully prepared to eliminate all interference effects. Theory has little to say about cases intermediate between these two extremes. Thus, if quantitative data are to be extracted from transmission measurements, some care must be... 

Figure 6. Instrumental schematic for vacuum UV photofragmentation-laser induced fluorescence measurement of ammonia SHGC, second harmonic generation crystal SFMC, sum frequency mixing crystal BS, beam splitter BD, beam dump TP, turning prism CL, cylindrical lens R, reflector TD, trigger diode OSC, oscillator cell AMP, amplifier cell BE, beam expander G, grating OC, output coupler M, mirror BC, beam combiner L, lens A, aperture PD, photodiode SC, sample cell RC, reference cell FP, filter pack SAM.PMT, sample cell photomultiplier REF.PMT, reference cell photomultiplier PP, additional photomultiplier port EX, exhaust and CGI, calibration gas inlet to flow line. (Reproduced with permission from reference 15. Copyright 1990 Optical Society of America.)...

The second (real) term accounts for the exponential decay of the electric field intensity in the direction normal to the interface. The reflected beam combines with the incident beam, forming a standing electromagnetic wave at the interface (Fig. 9.9). The electric field that penetrates to the optically rarer medium of refractive index n, the evanescent field, plays a critical role in many optical sensors based on the waveguiding principle. Its depth of penetration dv is defined as the distance at which the initial intensity Eq decays to 1/e of its value. Thus from (9.18), dv is... 

Fig. 6.8. A Principle of frequency-multiplexed CARS microspectroscopy A narrow-bandwidth pump pulse determines the inherent spectral resolution, while a broad-bandwidth Stokes pulse allows simultaneous detection over a wide range of Raman shifts. The multiplex CARS spectra shown originate from a 70 mM solution of cholesterol in CCI4 (solid line) and the nonresonant background of coverglass (dashed line) at a Raman shift centered at 2900 cm-1. B Energy level diagram for a multiplex CARS process. C Schematic of the multiplex CARS microscope (P polarizer HWP/QWP half/quarter-wave plate BC dichroic beam combiner Obj objective lens F filter A analyzer FM flip mirror L lens D detector S sample). D Measured normalized CARS spectrum of the cholesterol solution. E Maximum entropy method (MEM) phase spectrum (solid line) retrieved from (D) and the error background phase (dashed line) determined by a polynomial fit to those spectral regions without vibrational resonances. F Retrieved Raman response (solid line) calculated from the spectra shown in (E), directly reproducing the independently measured spontaneous Raman response (dashed line) of the same cholesterol sample...

An important test of a transient spectrometer s accuracy, stability, and noise level is provided by a baseline spectrum. This is an averaged spectrum obtained in exactly the same way as actual data, except that the ultraviolet excitation beam is kept blocked when it would otherwise be open. The lowest trace shown in Figure 2 is a typical 5-cycle baseline spectrum for our system. Systematic deviation from zero is less than 0. 01 absorbance units throughout, and the r. m. s. noise level varies from 0. 03 near the edges to 0. 007 near the center of the spectrum. These noise variations are inversely related to the detected single beam intensity spectrum, which drops on the blue side because of the continuum distribution and the transmissive properties of our beam combiner, and on the red side because of the photocathode response of the SIT detector head. A high degree of intensity linearity in the OMA is necessary for our... 

Fig. 8 Different types of interferometers - (a-d) Mach-Zehnder - (a) ion-exchange, (b) channelized, (c) ribbed, (d) ARROW, (e-h) Young - (e) using beam splitter for beam combining, (f) using lens for beam combining, (g, h) using dispersion for beam overlap in a side-by-side configuration, and (h) a sandwich configuration...

The key component in the FTIR system is theMichelson interferometer, as schematically illustrated in Figure 9.16. The infrared radiation from a source enters the Michelson interferometer. The interferometer is composed of one beam-splitter and two mirrors. The beam-splitter transmits half of the infrared (IR) beam from the source and reflects the other half. The two split beams strike a fixed mirror and a moving mirror, respectively. After reflecting from the mirrors, the two split beams combine at the beam-splitter again in order to irradiate the sample before the beams are received by a detector. 

The fluorescence detection system employed is shown in Figure 29.3. Both the IR and visible light ( 3 ps, 15 cm-1) generated by the picosecond laser system were introduced into a home-made laser fluorescence microscope [29, 30]. For the measurement of both solutions and fluorescent beads, both beams were adjusted onto a co-linear path by a beam-combiner and focused into the sample by an objective... 

IR and visible light beams were superposed onto a co-linear path by a beam-combiner, and focused into the sample by a CaF2 lens (f= 100 mm). The focal spot... 

While the use of direct absorption methods has grown, indirect action spectroscopic methods continue to be widely and successfully used in the study of neutral molecular clusters. As mentioned earlier, there are two commonly used detection methods, mass spectrometers and bolometers. Because of the variety of mass-spectroscopic methods, there is an equally wide range of techniques used in neutral cluster spectroscopy. One of the oldest among these involves electron-impact mass spectrometry of a cw neutral beam combined with vibrational predissociation spectroscopy using a tunable cw or pulsed laser. The advent of continuously tunable infrared sources (such as color center lasers and LiNbOa optical parametric oscillators) allowed for detailed studies of size and composition variation in neutral clusters. However, fragmentation of the clusters within the ionizer of the mass spectrometer, severely limited the identification of particular clusters with specific masses. Isotopic methods were able to mitigate some of the limitations, but only in a few cases. 

TABLE 4.1. Polarization Patterns at the Sample Surface During SRG Inscription Using a Variety of Polarized Beam Combinations. The "Quality" of the SRG (as Determined by Grating Height) Is Shown for Comparison... 

Recent developments for a balloon based experiment, BETTII (Rinehart et al. 2009 Rinehart 2010a,b, 2011 Rinehart and BETTII Team 2010 Leisawitz 2008), and space based spectral-spatial interferometers such as SPIRIT (Leisawitz et al. 2007, 2008 Leisawitz 2008), SPECS, FIRI have identified fhaf some technology needs to be developed and demonstrated, for example high sensitivity detectors (NEPs 10 ° W/Hz ), cooled apertures, beam combination and data processing algorithms. In all these proposals, the common point is the technique employed to perform observations, the Double Fourier Modulation. 

FISICA (Far Infrared Space Interferometer Critical Assessment) is also a three year project for the definition and technology development for the next generation THz space interferometry, more specifically to advance beam-combination, cryogenic delay lines, position metrology and to create a representative instrument simulator for a direct detection interferometer. The instrument simulator presented in this Thesis will form the basis of the first version of the FISICA simulator. 

Fig. 2.8 Schematic of an interferometer. Two telescopes collect the light that then travels along the delay lines DLl and DL2 and interferes at the beam combiner. The geometrical delay S is compensated with the delay Unes in order to find maximum fringe coherence to measure stellar positions. 0 is the view angle...

Initial alignment of the testbed was achieved with a continuous wave green laser mounted on the optical axis between the beam combiner and the detector, pointing in the direction of the source. The detector position was then set to provide maximum signal with the MAL source with the spectral arm a long way from the ZPD. 

If the two mirrors are equidistant from the beam splitter, the amplitudes of the two beams combine constructively. If one mirror is moved a distance of A/4, the emerging beam will be the result of two beams 180° out of phase and they will combine destructively. If the entering beam from the source is monochromatic, the detector will observe a cosine signal whose amplitude is a function of the mirror position. If the entering beam is polychromatic, the signal observed at the detector is a summation of all interferences as each... 

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