Beam Multiplexing Research Articles

Optically multiplexed multi-gas detection using quantum cascade laser photoacoustic spectroscopy

We report high-throughput, nondispersive optical multiplexing of laser beams using a scanning galvanometer. We have utilized this technique for multispecies trace-gas detection using multiple quantum cascade laser photoacoustic spectroscopy. We demonstrate switching from one laser to another in less than 1 s, a performance level needed for a comprehensive multispecies sensor, and a high signal-to-noise ratio detection of five gaseous components, NH(3), NO(2), dimethyl methyl phosphonate (DMMP, a simulant for nerve agents), acetone, and ethylene glycol, in a room air gas mixture containing approximately 3 ppb of NH(3), approximately 8 ppb of NO(2), approximately 20 ppb of DMMP, approximately 30 ppb of acetone, and approximately 40 ppb of ethylene glycol.

Phase-modulated multigroup volume holographic correlator

We propose a hybrid multiplexing method for volume holographic correlators based on the combination of orthogonal random phase modulation of an object beam and two-dimensional angular multiplexing of a reference beam. This method implements storing multiple groups of library images in a single storage location and outputting multiple groups of correlation spots by switching the modulation phase masks. Three experiments are designed to test the validity of this method.

Two-photon photostimulation and imaging of neural circuits

We introduce an optical method to stimulate individual neurons in brain slices in any arbitrary spatiotemporal pattern, using two-photon uncaging of MNI-glutamate with beam multiplexing. This method has single-cell and three-dimensional precision. By sequentially stimulating up to a thousand potential presynaptic neurons, we generated detailed functional maps of inputs to a cell. We combined this approach with two-photon calcium imaging in an all-optical method to image and manipulate circuit activity.

Beam Multiplexing Using the Phased-Array Weather Radar

Abstract The recently installed S-band phased-array radar (PAR) at the National Weather Radar Testbed (NWRT) offers fast and flexible beam steering through electronic beam forming. This capability allows the implementation of a novel scanning strategy termed beam multiplexing (BMX), with the goal of providing fast updates of weather information with high statistical accuracy. For conventional weather radar the data acquisition time for a sector scan or a volume coverage pattern (VCP) can be reduced by increasing the antenna’s rotation rate to the extent that the pedestal allows. However, statistical errors of the spectral moment estimates will increase due to the fewer samples that are available for the estimation. BMX is developed to exploit the idea of collecting independent samples and maximizing the usage of radar resources. An improvement factor is introduced to quantify the BMX performance, which is defined by the reduction in data acquisition time using BMX when the same data accuracy obtained by a conventional scanning strategy is maintained. It is shown theoretically that a fast update without compromising data quality can be achieved using BMX at small spectrum widths and a high signal-to-noise ratio (SNR). Applications of BMX to weather observations are demonstrated using the PAR, and the results indicate that an average improvement factor of 2–4 can be obtained for SNR higher than 10 dB.

Application of multiline two-photon microscopy to functional in vivo imaging

High spatial resolution and low risks of photodamage make two-photon laser-scanning microscopy (TPLSM) the method of choice for biological imaging. However, the study of functional dynamics such as neuronal calcium regulation often also requires a high temporal resolution. Hitherto, acquisition speed is usually increased by line scanning, which restricts spatial resolution to structures along a single axis. To overcome this gap between high spatial and high temporal resolution we performed TPLSM with a beam multiplexer to generate multiple laser foci inside the sample. By detecting the fluorescence emitted from these laser foci with an electron-multiplying camera, it was possible to perform multiple simultaneous linescans. In addition to multiline scanning, the array of up to 64 laser beams could also be used in x– y scan mode to collect entire images at high frame rates. To evaluate the applicability of multiline TPLSM to functional in vivo imaging, calcium signals were monitored in visual motion-sensitive neurons in the brain of flies. The capacity of our method to simultaneously acquire signals at different cellular locations is exemplified by measurements at branched neurites and ‘spine’-like structures. Calcium dynamics depended on branch size, but ‘spines’ did not systematically differ from their ‘parent neurites’. The spatial resolution of our setup was critically evaluated by comparing it to confocal microscopy and the negative effect of scattering of emission light during image detection was assessed directly by running the setup in both imaging and point-scanning mode.

Laser Beam Shaping by Computer Generated Hologram

A computer generated hologram (CGH) is a useful tool for various optical applications, such as beam multiplexing, patterning, beam homogenizer, etc. The precise technologies are important issue for the fabrication of CGH, and the algorithm is more essential for designing it. I discuss the detailed consideration on the CGH design which is required to reconstruct a complex image. I also introduce efficient methods to design a hologram which creates a desired pattern at the Fresnel region and on a spherical surface.

Fourier gratings as submillimeter beam splitters

Over the past years, a number of groups have developed phase gratings as local oscillator beam multiplexers for array receivers in the submillimeter wavelength domain. The most popular type of grating is the Dammann (1977) grating, a simple and versatile binary phase grating. We introduce a new type of grating, the Fourier grating, which, in contrast to the binary structure of Dammann gratings, uses a smooth grating structure. Due to the lack of sharp edges these gratings can be manufactured with high precision as reflection gratings even for two-dimensional (2-D) dispersion. Fourier gratings are designed using a simple optimization procedure that only involves a small number of parameters. Their diffraction efficiency is very high. We have produced a number of gratings and tested them at a frequency of 490 GHz, verifying the theoretical results.

Zone-plate-array lithography in the deep ultraviolet

We describe initial steps we have taken in the development of zone-plate-array lithography (ZPAL), a proposed new paradigm for sub-100 nm lithography. The optimal implementation of ZPAL would employ an undulator emitting soft x rays of 4.5 nm wavelength. However, we have opted to concentrate initially on the major uncertainties associated with ZPAL: (1) fabrication of a large array of zone plates with a center-to-center spacing accuracy finer than the minimum zone width, (2) multiplexing of input beams to the individual zone plates, and (3) coordination of that multiplexing with precision motion of a substrate stage. We fabricated arrays of pure-phase zone plates suitable for the 193 nm output of an ArF laser, and conducted exposure tests using a modified Michelson configuration for focusing the zone plate array on the substrate. We also show the first example of simplistic writing. We show that the micromirror array manufactured by Texas Instruments, for use in projection displays, has dimensions and switching characteristics close to those needed for an ultimate ZPAL system.

Diamond single crystals: the ultimate monochromator material for high-power x-ray beams

A review of the performance of diamond single crystals as a high heat load optical component for synchrotron x rays is given. It has been proven experimentally that the bandpass and the angular divergence of the monochromatic beam provided by a relatively thin diamond crystal used in an undulator beam are not degraded by thermal effects for a total power up to 280 W (8.7 W absorbed) at a heat flux up to 3.5 kW/mm² (109 W/mm² absorbed). These high heat load tests and model calculations have shown that edge-cooled diamond crystals at room temperature provide an easy and widely satisfactory solution to the heat load problems generated by undulator beams that are currently foreseen at the third-generation storage rings of the European Synchrotron Radiation Facility, the Advanced Photon Source, and the SPring-8 facilities. For this cooling geometry, diamond single crystals offer the additional advantage that beam multiplexing can be used. Currently available synthetic diamond crystals are sufficiently big for undulator beams and their crystalline perfection is adequate. Most of the crystals actually in use were prepared with their big surfaces (about 30 mm² in size) oriented parallel to the (100) netplanes, but more recently bigger samples whose surfaces are parallel to the (111) lattice planes were obtained. Thus, diamond single crystals are superior to all other monochromator materials for undulators and for cases where a loss of a factor of 2 in flux combined with a similar gain in resolution (as compared to silicon) are compatible with the experiments.

The Troika Beamline at ESRF (abstract)

The Troika Beamlime at ESRF is based on the concept of beam multiplexing by using x‐ray transparent diamond and/or beryllium monochromators. The favorable thermal and crystallographic properties of perfect diamond are well matched to the characteristics of the new low emittance undulator sources. A series of such transmission monochromators can use the same white beam and supply several experimental stations simultaneously with monochromatic x‐rays of slightly different energies. The first experimental station of the Troika beamline is operating and the multiplexing mode has been tested successfully. First experiments including protein crystallography, resonant magnetic scattering, liquid surface diffraction, and scattering with coherent x‐rays were carried out during the commissioning period and the results demonstrate the wide potential of third‐generation synchrotron sources.

KrF laser produced plasmas

KrF and other short wavelength lasers are ideal candidates for producing hot dense plasmas since the laser energy can be absorbed with high efficiency by classical mechanisms, thereby virtually eliminating anomalous absorption and the production of non-thermal electrons. A high power KrF laser system employing optical beam multiplexing and stimulated Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011−1014 W/cm2 has been developed for producing such plasmas and studying laser/plasma interaction phenomena. A variety of studies on absorption, transport, ablation, X-ray conversion and stimulated scattering instabilities have been pursued with this ¼ μm laser on single atomic number and multi-layer targets. This paper briefly describes some of the features of the KrF laser system and highlights some of the characteristics of the hot dense plasmas produced.

Multispecies coherent anti-Stokes Raman scattering instrument for turbulent combustion

A nonintrusive diagnostic system is described which permits simultaneous measurement of temperature, nitrogen number density, and oxygen number density in hostile combustion environments. This system is pumped by a 10-Hz neodymium YAG laser, and signals are detected with an intensified photodiode array and dual photomultipliers. The system utilizes a folded BOXCARS beam arrangement, two probe dye lasers, dynamic range expansion, polarization rejection of nonresonant background, and multiplexing of the signal beams.

Beam compression and beam multiplexing in a time-of-flight mass spectrometer

Two new methods for operating a time-of-flight mass spectrometer are suggested. The first is a beam compression method which allows separation of one kind of particle (one m/q ratio) at a time, from a beam continously emitted by an ion source. Due to the continuous operation of the source a corresponding increase in signal-to-noise ratio is expected. The second method is based on forming a multiplex beam by modulating a continuously emitted ion beam. The use of a time array detector enables the collection of the data. The algorithm of analysis is presented. This method should have the increased throughput advantage. An improvement in signal-to-noise ratio need not take place.

Experimental results for high intensity KrF laser/plasma interaction

A high power KrF laser system employing beam multiplexing and stimulated Raman or Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011 to 1014 W/cm2 has been developed for laser/plasma interaction research. A variety of investigations have been pursued on single and multilayer targets with variable atomic numbers. Absorption, transport, X-ray conversion, ion expansion characteristics, mass ablation and ablation pressure scaling, and stimulated scattering instabilities are among features that have been studied as a function of laser intensity. A wide variety of laser and target diagnostics are employed including focal plane imaging cameras for energy distribution and UV and soft X-ray streak cameras for temporally resolving the incident laser pulse and X-ray emission. Experimental results will be presented and our current understanding of the KrF laser/plasma interaction will be discussed.

Binary holographic LO beam multiplexer for IR imaging detector arrays

A binary holographic technique for infrared laser beam multiplexing is described. The technique was used to generate amplitude distribution matched and phase matched local oscillators for a heterodyne IR imaging detector array. It uses a high accuracy interlaced binary diffraction grating to multiplex single LO wave fronts.