Volume 77, Issue 6, June 2006
- optics; atoms and molecules; spectroscopy; photon detectors
- particle sources, optics and acceleration; particle detectors
- nuclear physics, fusion and plasmas
- microscopy and imaging
- condensed matter; materials
- biology and medicine
- electronics; electromagnetic technology; microwaves
- thermometry; thermal diffusivity; acoustic; photothermal and photoacoustic
- general instruments
Index of content:
- OPTICS; ATOMS AND MOLECULES; SPECTROSCOPY; PHOTON DETECTORS
77(2006); http://dx.doi.org/10.1063/1.2204577View Description Hide Description
We report the design and performance of a simple radio-frequency generator, suitable for driving capacitive loads such as ion traps in the few to thousand picofarad range. The oscillation frequency can be phase locked to an external reference oscillator, providing excellent frequency stabilization. Amplitude control circuits allow the oscillations to be rapidly started and stopped.
77(2006); http://dx.doi.org/10.1063/1.2204582View Description Hide Description
Traditional integrating spheres, which use a single detector to measure luminous flux, have a number of drawbacks associated with the sources of error caused by baffling, nonideal topology, and variations in surface reflectance. In this article we address the potential drawbacks of many traditional integrating spheres and present a new instrument which achieves accurate measurements without the use of baffles, by relying on optical fibers to distribute measurement points around the interior of a highly reflective structure.
77(2006); http://dx.doi.org/10.1063/1.2200766View Description Hide Description
The dynamic observation and characterization of light emission following the detonation and subsequent combustion of an aluminized explosive is described. The temporal, spatial, and spectral specificity of the light emission are achieved using a combination of optical diagnostics. Aluminum and aluminum monoxide emission peaks are monitored as a function of time and space using streak camera based spectroscopy in a number of light collection configurations. Peak areas of selected aluminum containing species are tracked as a function of time to ascertain the relative kinetics (growth and decay of emitting species) during the energetic event. At the chosen streak camera sensitivity, aluminum emission is observed for following the detonation of a confined charge of PBXN-113, while aluminum monoxide emission persists longer than . A broadband optical emission gauge, shock velocity gauge, and fast digital framing camera are used as supplemental optical diagnostics. In-line, collimated detection is determined to be the optimum light collection geometry because it is independent of distance between the optics and the explosive charge. The chosen optical configuration also promotes a constant cylindrical collection volume that should facilitate future modeling efforts.
77(2006); http://dx.doi.org/10.1063/1.2205622View Description Hide Description
Fourier transform infrared (FTIR)spectrometer is a powerful tool for studying the photoluminescence(PL) properties of semiconductors, due to its well-known multiplexing and throughput advantages. However, it suffers from internal He–Ne laser disturbance in near-infrared and∕or environmental background thermal emission in mid- and far-infrared spectral regions. In this work, a modulated PL technique is developed based on step-scan (SS)-FTIR spectrometer. Theoretical analysis is conducted, and applications of the technique are given as examples in the PL study of mid-infrared HgCdTe thin films and near-infrared multiple quantum wells, respectively. The results indicate that the He–Ne laser and∕or thermal emission disturbance can be reduced at least and∕or even , respectively, by the modulated SS-FTIR PL technique, and hence a rather smooth PLspectrum can be obtained even under room temperature for HgCdTe thin films. A brief comparison is given of this technique with previously reported phase-sensitive modulation methods based on conventional rapid-scan (RS)-FTIR spectrometer, and the advantages of this technique over the former RS- FTIR-based ones are emphasized.
77(2006); http://dx.doi.org/10.1063/1.2209954View Description Hide Description
Automation of x-rayabsorptionspectroscopic(XAS)data reduction is essential to cope with high-throughput data collection becoming available at an increasing number of synchrotron radiation centers. A flexible script called KEMP has been developed and implemented at the XAS beamline at EMBL Hamburg. It automatically processes fluorescenceXAS data. The pipeline includes dead time correction, energy calibration, selection of fluorescence detector channels, as well as the extraction of x-rayabsorption near-edge structure and extended x-ray-absorption fine structure. The output is quickly available and thus can be included in the design of further experiments, which results in a more efficient use of the beam time.
Power spectrum analysis for optical tweezers. II: Laser wavelength dependence of parasitic filtering, and how to achieve high bandwidth77(2006); http://dx.doi.org/10.1063/1.2204589View Description Hide Description
In a typical optical tweezers detection system, the position of a trapped object is determined from laser light impinging on a quadrant photodiode. When the laser is infrared and the photodiode is of silicon, they can act together as an unintended low-pass filter. This parasitic effect is due to the high transparency of silicon to near-infrared light. A simple model that accounts for this phenomenon [Berg-Sørensen et al., J. Appl. Phys.93, 3167 (2003)] is here solved for frequencies up to and for laser wavelengths between 750 and . The solution is applied to experimental data in the same range, and is demonstrated to give this detection system of optical tweezers a bandwidth, accuracy, and precision that are limited only by the data acquisition board’s bandwidth and bandpass ripples, here and , respectively.
77(2006); http://dx.doi.org/10.1063/1.2204623View Description Hide Description
We have designed and constructed a new flat-field-type slit-less soft x-ray emission spectrometer that enables high detection efficiency and high energy resolution in the energy range of . The energy resolution is optimized in the C and O regions, where the maximum energy resolution of 2500 is expected using a focused beam whose spot size is full width at half maximum in the vertical direction. A distortion of the linear profile of the focused image on the charge-coupled device(CCD)detector is successfully removed by using a cylindrical grating. This enabled us to apply a super-resolution reconstruction technique to compensate for the lack of spatial resolution of the CCDdetector.
77(2006); http://dx.doi.org/10.1063/1.2209957View Description Hide Description
We have developed an apparatus which allows measuring the sticking cross section of a neutral atom onto a mass selected charged cluster of known temperature. The main point is to reduce the kinetic energy dispersion in the mass selected cluster beam in order to work with ions of very low (near thermal) kinetic energy. A novel device is presented which focuses in energy with only a small loss in the beam intensity. An application is shown to the sticking of sodium atoms onto sodiumclusters at an energy of a few tenths of an eV in the center-of-mass frame.
Automatic tracing of interference fringes using Fourier filtering, local averaging, and local-scan-type determination77(2006); http://dx.doi.org/10.1063/1.2209958View Description Hide Description
Interferograms are made by interfering wave fronts and hence contain important information about them. Analysis of interferograms requires the identification of all the fringes and their extrema. Here an algorithm for computer tracing of interference fringes is described. The method uses a Fourier filter for removing high frequency noise, a local averaging for binarization of images not having uniform intensity distribution, scanning the interferogram locally both horizontally and vertically to determine the type of the scan, local application of simultaneous horizontal and vertical scans for tracing of complicated fringe patterns, and removal of the noise from the traces by determining the number of connected pixels. The proposed algorithm was found to yield good result even for high noise images.
77(2006); http://dx.doi.org/10.1063/1.2209970View Description Hide Description
We have developed and characterized a measurement setup for measuring the spectralirradiance responsivity of broadband UV detectors. The setup consists of a single gratingmonochromator and a powerful Xe source to maximize the output power and thus enable spectral measurements with broadband detectors, whose sensitivity is typically low. Commercial UVA and UVB detectors were characterized with the setup. The results of the UVA detector were verified with a spectroradiometric calibration, and the results of the two methods agreed within 1.2%. The uncertainties (coverage factor ) were 2.0% [method utilizing ] and 3.1% (spectroradiometric method). Also the applicability of a correction factor for transforming calibration results between light sources was tested, and the obtained correction agreed with measurement results.
77(2006); http://dx.doi.org/10.1063/1.2209971View Description Hide Description
We present a stabilized semiconductor laser system designed to operate as a fiber-optic front-end master oscillator of a pulsed high-power iodine laser Prague Asterix Laser System (PALS). The replacement of the PALS master oscillator is a part of a broader effort to rebuild PALS into a laser generating shorter pulses with higher pulse power by the technique of optical parametric chirped pulse amplification. With an operating wavelength of the stabilized laser master oscillator is based on a telecommunication single-frequency distributed feedback diode. The frequency stabilization is derived from transitions in thermally dissociated iodine. Locking to the selected transition is fully automatic and the control system employs a unique combination of control loops derived from temperature and absorption to overcome the problem of narrow locking range of a single absorption line.
77(2006); http://dx.doi.org/10.1063/1.2213213View Description Hide Description
We constructed a super-resolution microscope system based on a cw laser light source. Electro-optical modulators convert the cw laser light into a light pulse with a width of and provide a repetition rate of . The performance of the microscope was evaluated using fluorescence microbeads. The fluorescence signal from the beads can be detected with very low statistical fluctuation. The super-resolution image was obtained with better signal to noise ratio compared with that given by a pulse laser light source with a repetition rate of several tens of hertz. The fluorescent size of the beads was , which is 2.3 times smaller than the diffraction limit. Experimental results confirmed that the two-point resolution also overcomes the diffraction limit. The constructed system is expected to become a commercial microscope.
77(2006); http://dx.doi.org/10.1063/1.2198791View Description Hide Description
Parabolic planar compound refractive lenses (CRLs) made from glassycarbon by means of laser ablation are presented. They have radii of curvatures of 5 and and geometric apertures of 40 and , respectively. The numbers of biconcave elements in the CRLs were 4, 7, and 200. The planar lenses allow formation of a linear focus of length comparable with the depths of their profiles. Usage of two CRLs in a crossed geometry provides formation of two-dimensional focus. The lenses were tested at the European Synchrotron Radiation Facility at the bending magnet beam line BM-5. The minimum experimental size of the focus has been achieved as .
77(2006); http://dx.doi.org/10.1063/1.2213216View Description Hide Description
In order to generate high-average-power extreme ultraviolet radiation around from laser-produced plasma, a fast rotating cryogenic drum system which can continuously supply a solid Xe target for high-repetition laser pulses has been developed. It was successfully operated at a rotating speed of and an up-down speed of . The growth rate of the solid Xe layer is kept at a constant speed (for example, ) with a constant rate of Xe input flow, independent of the rotating speed. It has been demonstrated that wipers play an important role in recovering the laser craters with a recovery rate of . These performances allow laser illuminations on the solid Xe target with a pulse repetition rate of without overlapping laser craters.
Broadband high-resolution elliptical crystal x-ray spectrometer for high energy density physics experiments77(2006); http://dx.doi.org/10.1063/1.2214688View Description Hide Description
The spectroscopic investigation of high temperature laser produced plasmas in general, and x-rayopacity experiments in particular, often requires instruments with both a broad coverage of x-ray energies and high spectral,spatial, and temporal resolution. We analyze the design, model the response, and report the commissioning of a spectrometer using elliptical crystals in conjunction with a large format, gated microchannel plate detector.Measurements taken with this instrument at the Janus laser facilities demonstrate the designed spectral range of and spectral resolution , resulting in two to three times more spectral data than achieved by previous spectrometer designs. The observed temporal resolution and spatial resolution are consistent with the requirements of high energy density opacity experiments.
Versatile optical manipulation system for inspection, laser processing, and isolation of individual living cells77(2006); http://dx.doi.org/10.1063/1.2214961View Description Hide Description
Isolation of individual cells from a heterogeneous cell population is an invaluable step in the analysis of single cell properties. The demands in molecular and cellular biology as well as molecular medicine are the selection, isolation, and monitoring of single cells and cell clusters of biopsy material. Of particular interest are methods which complement a passive optical or spectroscopic selection with a variety of active single cell processing techniques such as mechanical, biochemical, or genetic manipulation prior to isolation. Sophisticated laser-based cell processing systems are available which can perform single cell processing in a contact-free and sterile manner. Until now, however, these multipurpose turnkey systems offer only basic micromanipulation and are not easily modified or upgraded, whereas laboratory situations often demand simple but versatile and adaptable solutions. We built a flexible laser micromanipulation platform combining contact-free microdissection and catapulting capabilities using a pulsed ultraviolet laser with simultaneous generation of optical tweezing forces using a continuous wave infrared laser. The potential of our platform is exemplified with techniques such as local laser-induced injection of biomolecules into individual living cells, laser surgery, isolation of single cells by laser catapulting, and control of neuronal growth using optical gradient forces. Arbitrary dynamic optical force patterns can be created by fast laser scanning with acousto-optical deflectors and galvanometer mirrors, allowing multibeam contact-free micromanipulation, a prerequisite for reliable handling of material in laboratory-on-a-chip applications. All common microscopy techniques can be used simultaneously with the offered palette of micromanipulation methods. Taken together, we show that advanced optical micromanipulation systems can be designed which combine quality, cost efficiency, and adaptability.
77(2006); http://dx.doi.org/10.1063/1.2216567View Description Hide Description
We report the design, construction, and evaluation of a midinfrared continuous wave cavity ring-down spectrometer based on a lead salt diode laser. A pulsed molecular beam assembly with a homemade slit nozzle was constructed and incorporated into the spectrometer. A computer program was developed to automate and to synchronize the timing of the cavity ring-down experiments with the pulsed molecular beam. To initiate a cavity ring-down event, a frequency detuning scheme is exploited to effectively block the laser from entering the ring-down cavity by rapidly shifting the laser frequency. The standard deviation of the experimental ring-down time, i.e., , was 0.63%, corresponding to a noise-equivalent absorption of at a fixed laser frequency with an evacuated cavity with ten averaging cycles. A room temperature infrared spectrum of methane and a jet cooled infrared spectrum of propylene oxide at are presented.
Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases77(2006); http://dx.doi.org/10.1063/1.2216907View Description Hide Description
We present and characterize an experimental system in which we achieve the integration of an ultrahigh finesse optical cavity with a Bose-Einstein condensate(BEC). The conceptually novel design of the apparatus for the production of BECs features nested vacuum chambers and an in vacuo magnetic transport configuration. It grants large scale spatial access to the BEC for samples and probes via a modular and exchangeable “science platform.” We are able to produce condensates of atoms and to output couple continuous atom lasers. The cavity is mounted on the science platform on top of a vibration isolation system. The optical cavity works in the strong coupling regime of cavity quantum electrodynamics and serves as a quantum optical detector for single atoms. This system enables us to study atom optics on a single particle level and to further develop the field of quantum atom optics. We describe the technological modules and the operation of the combined BECcavity apparatus. Its performance is characterized by single atom detection measurements for thermal and quantum degenerate atomic beams. The atom laser provides a fast and controllable supply of atoms coupling with the cavity mode and allows for an efficient study of atom field interactions in the strong coupling regime. Moreover, the high detection efficiency for quantum degenerate atoms distinguishes the cavity as a sensitive and weakly invasive probe for cold atomic clouds.
- PARTICLE SOURCES, OPTICS AND ACCELERATION; PARTICLE DETECTORS
77(2006); http://dx.doi.org/10.1063/1.2206778View Description Hide Description
We describe the design, electronics, and test results of a simple and low-cost time-of-flight ion charge-to-massanalyzer that is suitable for ion source characterization. The method selects a short-time sample of the beam whose charge-to-mass composition is then separated according to ion velocity and detected by a remote Faraday cup. The analyzer is a detachable device that has been used for rapid analysis of charge-to-mass composition of ion beams accelerated by voltages of up to about .
77(2006); http://dx.doi.org/10.1063/1.2206561View Description Hide Description
A compact positron accumulator based upon a simple two-stage buffer gas cooling scheme is described. Its operation to produce wide bursts containing around positrons with cycling times in the range is discussed. Departures of the behavior of the accumulator from that expected of such an instrument are presented. The utility of these effects in diagnosing accumulator performance is described.