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May 2012

Volume 83, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 051101 (2012); http://dx.doi.org/10.1063/1.4709621 (18 pages)

Igor Lubomirsky and Oscar Stafsudd

The periodic pulsed heating technique for measuring pyroelectricity (the Chynoweth method) is one of several measurement techniques that have been significantly enhanced through advances in instrumentation such as fast digital averaging oscilloscopes and modulated light sources.

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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Detection of nanosecond-scale, high power THz pulses with a field effect transistor

S. Preu, H. Lu, M. S. Sherwin, and A. C. Gossard

Rev. Sci. Instrum. 83, 053101 (2012); http://dx.doi.org/10.1063/1.4705986 (6 pages)

Online Publication Date: 1 May 2012

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We demonstrate detection and resolution of high power, 34 ns free electron laser pulses using a rectifying field effect transistor. The detector remains linear up to an input power of 11 ± 0.5 W at a pulse energy of 20 ± 1 μJ at 240 GHz. We compare its performance to a protected Schottky diode, finding a shorter intrinsic time constant. The damage threshold is estimated to be a few 100 W. The detector is, therefore, well-suited for characterizing high power THz pulses. We further demonstrate that the same detector can be used to detect low power continuous-wave THz signals with a post detection limited noise floor of 3.1 μW/math. Such ultrafast, high power detectors are important tools for high power and high energy THz facilities such as free electron lasers.
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41.60.Cr Free-electron lasers
42.60.-v Laser optical systems: design and operation

Realization of autofocusing system for laser direct writing on non-planar surfaces

Jianbo Luo, Yiyong Liang, and Guoguang Yang

Rev. Sci. Instrum. 83, 053102 (2012); http://dx.doi.org/10.1063/1.4709407 (5 pages)

Online Publication Date: 2 May 2012

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This paper presents an autofocusing system for laser direct writing on non-planar surfaces, including focus error signal detection and focusing control. The focus error signal detection is based on modified confocal techniques, which features easy implementation, independence of the tilt angles of non-planar surfaces, and excellent suppression of common-mode noise or variable system factors. We also present a macro/micro dual-drive mechanism and its synchronous operation for focusing control on non-planar surfaces. Finally, a performance evaluation of the autofocusing system is presented. The uniform line width of 2.1 μm for a pattern on a convex spherical substrate with a curvature radius of 100 mm shows the autofocusing system performs well.
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42.62.-b Laser applications

Enhancing photocurrent transient spectroscopy by electromagnetic modeling

H. Diesinger, M. Panahandeh-Fard, Z. Wang, D. Baillargeat, and C. Soci

Rev. Sci. Instrum. 83, 053103 (2012); http://dx.doi.org/10.1063/1.4710996 (6 pages)

Online Publication Date: 3 May 2012

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The shape and duration of photocurrent transients generated by a photoconductive switch depend on both the intrinsic response of the active material and the geometry of the transmission line structure. The present electromagnetic model decouples both shape forming contributions. In contrast to previously published work, it accounts for the particular operating mode of transient spectroscopy. The objective is to increase the time resolution by two approaches, by optimizing structural response and by deconvolving it from experimental data. The switch structure is represented by an effective transimpedance onto which the active material acts as current generator. As proof of concept, the response of a standard microstrip switch is modeled and deconvolved from experimental data acquired in GaAs, yielding a single exponential material response and hence supporting the validity of the approach. Beyond compensating for the response deterioration by the structure, switch architectures can be a priori optimized with respect to frequency response. As an example, it is shown that a microstrip gap that can be deposited on materials incompatible with standard lithography reduces pulse broadening by an order of magnitude if it is provided with transitions to coplanar access lines.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
11.55.-m S-matrix theory; analytic structure of amplitudes

An in situ set up for the detection of CO2 from catalytic CO oxidation by using planar laser-induced fluorescence

J. Zetterberg, S. Blomberg, J. Gustafson, Z. W. Sun, Z. S. Li, E. Lundgren, and M. Aldén

Rev. Sci. Instrum. 83, 053104 (2012); http://dx.doi.org/10.1063/1.4711130 (5 pages)

Online Publication Date: 4 May 2012

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We report the first experiment carried out on an in situ setup, which allows for detection of CO2 from catalytic CO oxidation close to a model catalyst under realistic reaction conditions by the means of planar laser-induced fluorescence (PLIF) in the mid-infrared spectral range. The onset of the catalytic reaction as a function of temperature was followed by PLIF in a steady state flow reactor. After taking into account the self-absorption of CO2, a good agreement between the detected CO2 fluorescence signal and the CO2 mass spectrometry signal was shown. The observed difference to previously measured onset temperatures for the catalytic ignition is discussed and the potential impact of IR-PLIF as a detection technique in catalysis is outlined.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
42.62.-b Laser applications

Response of large area avalanche photodiodes to low energy x rays

T. R. Gentile, M. Bales, U. Arp, B. Dong, and R. Farrell

Rev. Sci. Instrum. 83, 053105 (2012); http://dx.doi.org/10.1063/1.4714348 (9 pages) | Cited 1 time

Online Publication Date: 8 May 2012

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For an experiment to study neutron radiative beta-decay, we operated large area avalanche photodiodes (APDs) near liquid nitrogen temperature to detect x rays with energies between 0.2 keV and 20 keV. Whereas there are numerous reports of x ray spectrometry using APDs at energies above 1 keV, operation near liquid nitrogen temperature allowed us to reach a nominal threshold of 0.1 keV. However, due to the short penetration depth of x rays below 1 keV, the pulse height spectrum of the APD become complex. We studied the response using monochromatic x ray beams and employed phenomenological fits of the pulse height spectrum to model the measurement of a continuum spectrum from a synchrotron. In addition, the measured pulse height spectrum was modelled using a profile for the variation in efficiency of collection of photoelectrons with depth into the APD. The best results are obtained with the collection efficiency model.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
07.85.Nc X-ray and γ-ray spectrometers

Fourier transform infrared spectroscopy approach for measurements of photoluminescence and electroluminescence in mid-infrared

Y. G. Zhang, Y. Gu, K. Wang, X. Fang, A. Z. Li, and K. H. Liu

Rev. Sci. Instrum. 83, 053106 (2012); http://dx.doi.org/10.1063/1.4717673 (7 pages) | Cited 5 times

Online Publication Date: 11 May 2012

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An improved Fourier transform infrared spectroscopy approach adapting to photoluminescence and electroluminescence measurements in mid-infrared has been developed, in which diode-pumped solid-state excitation lasers were adopted for photoluminescence excitation. In this approach, three different Fourier transform infrared modes of rapid scan, double modulation, and step scan were software switchable without changing the hardware or connections. The advantages and limitations of each mode were analyzed in detail. Using this approach a group of III–V and II–VI samples from near-infrared extending to mid-infrared with photoluminescence intensities in a wider range have been characterized at room temperature to demonstrate the validity and overall performances of the system. The weaker electroluminescence of quantum cascade lasers in mid-infrared band was also surveyed at different resolutions. Results show that for samples with relatively strong photoluminescence or electroluminescence out off the background, rapid scan mode is the most preferable. For weaker photoluminescence or electroluminescence overlapped with background, double modulation is the most effective mode. To get a better signal noise ratio when weaker photoluminescence or electroluminescence signal has been observed in double modulation mode, switching to step scan mode should be an advisable option despite the long data acquiring time and limited resolution.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.70.Hj Laser materials
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.55.Et II-VI semiconductors
78.60.Fi Electroluminescence

A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy

A. Y. Elezzabi and P. Maraghechi

Rev. Sci. Instrum. 83, 053107 (2012); http://dx.doi.org/10.1063/1.4717732 (6 pages)

Online Publication Date: 14 May 2012

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A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.Fm Reflectors, beam splitters, and deflectors

An apparatus for immersing trapped ions into an ultracold gas of neutral atoms

Stefan Schmid, Arne Härter, Albert Frisch, Sascha Hoinka, and Johannes Hecker Denschlag

Rev. Sci. Instrum. 83, 053108 (2012); http://dx.doi.org/10.1063/1.4718356 (10 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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We describe a hybrid vacuum system in which a single ion or a well-defined small number of trapped ions (in our case Ba+ or Rb+) can be immersed into a cloud of ultracold neutral atoms (in our case Rb). This apparatus allows for the study of collisions and interactions between atoms and ions in the ultracold regime. Our setup is a combination of a Bose-Einstein condensation apparatus and a linear Paul trap. The main design feature of the apparatus is to first separate the production locations for the ion and the ultracold atoms and then to bring the two species together. This scheme has advantages in terms of stability and available access to the region where the atom-ion collision experiments are carried out. The ion and the atoms are brought together using a moving one-dimensional optical lattice transport which vertically lifts the atomic sample over a distance of 30 cm from its production chamber into the center of the Paul trap in another chamber. We present techniques to detect and control the relative position between the ion and the atom cloud.
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37.10.Ty Ion trapping
42.50.Wk Mechanical effects of light on material media, microstructures and particles
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
37.10.Rs Ion cooling
34.50.-s Scattering of atoms and molecules
37.10.Jk Atoms in optical lattices

Multiplex and simultaneous measurement of displacement and temperature using tapered fiber and fiber Bragg grating

Chongke Ji, Chun-Liu Zhao, Juan Kang, Xinyong Dong, and Shangzhong Jin

Rev. Sci. Instrum. 83, 053109 (2012); http://dx.doi.org/10.1063/1.4718360 (5 pages)

Online Publication Date: 17 May 2012

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A simple method to work out the multiplexing of tapered fiber based sensors is proposed and demonstrated. By cascading a tapered fiber with a fiber Bragg grating (FBG), the sensor head is provided with a wavelength identification, different FBGs provide the sensor heads with different reflective peaks and they can be distinguished in optical spectrum. By compositing several such sensor heads with a multi-channel beam splitter, a star-style topological structure sensor for multipoint sensing is achieved. At the same time, the output intensity at the peak wavelength is sensitive to one external physical parameter applied on the related FBG-cascaded tapered fiber and the central wavelength of the peak is only sensitive to temperature, so that that parameter and temperature can be measured simultaneously. A sensor for dual-point measurement of the displacement and temperature simultaneously is experimentally demonstrated by using a 2 × 2 coupler in this paper. Experiment results show that the sensor works well and the largest sensitivities reach to 0.11 dB/μm for displacement in the range of 0–400 μm, and ∼0.0097 nm/°C for temperature between 20 °C and 70 °C.
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42.81.Pa Sensors, gyros
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.79.Dj Gratings

Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

P. Grossmann, I. Rajkovic, R. Moré, J. Norpoth, S. Techert, C. Jooss, and Klaus Mann

Rev. Sci. Instrum. 83, 053110 (2012); http://dx.doi.org/10.1063/1.4718936 (4 pages) | Cited 1 time

Online Publication Date: 17 May 2012

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We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1–5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the “water-window” region (2.28 nm–4.36 nm) on the manganite Pr0.7Ca0.3MnO3, investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.
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07.60.-j Optical instruments and equipment
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Simultaneous translational temperature measurements of different atomic species in plasma flows using scanning Fabry-Perot interferometry

Stefan Löhle and Sebastian Lein

Rev. Sci. Instrum. 83, 053111 (2012); http://dx.doi.org/10.1063/1.4719919 (7 pages)

Online Publication Date: 21 May 2012

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A revised scientific instrument to measure simultaneously kinetic temperatures of different atoms from their optical emission profile is reported. Emission lines are simultaneously detected using one single scanning Fabry-Perot-interferometer (FPI) for a combined spectroscopic setup to acquire different emission lines simultaneously. The setup consists in a commercial Czerny-Turner spectrometer configuration which is combined with a scanning Fabry-Perot interferometer. The fast image acquisition mode of an intensified charge coupled device camera allows the detection of a wavelength interval of interest continuously while acquiring the highly resolved line during the scan of the FPI ramp. Results using this new setup are presented for the simultaneous detection of atomic nitrogen and oxygen in a high enthalpy air plasma flow as used for atmospheric re-entry research and their respective kinetic temperatures derived from the measured line profiles. The paper presents the experimental setup, the calibration procedure, and an exemplary result. The determined temperatures are different, a finding that has been published so far as due to a drawback of the experimental setup of sequential measurements, and which has now to be investigated in more detail.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.30.-q Plasma dynamics and flow
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Kn Thermodynamics of plasmas

A Rayleigh-Brillouin scattering spectrometer for ultraviolet wavelengths

Ziyu Gu (谷子羽), M. Ofelia Vieitez, Eric-Jan van Duijn, and Wim Ubachs

Rev. Sci. Instrum. 83, 053112 (2012); http://dx.doi.org/10.1063/1.4721272 (7 pages) | Cited 1 time

Online Publication Date: 24 May 2012

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A spectrometer for the measurement of spontaneous Rayleigh-Brillouin (RB) scattering line profiles at ultraviolet wavelengths from gas phase molecules has been developed, employing a high-power frequency-stabilized UV-laser with narrow bandwidth (2 MHz). The UV-light from a frequency-doubled titanium:sapphire laser is further amplified in an enhancement cavity, delivering a 5 W UV-beam propagating through the interaction region inside a scattering cell. The design of the RB-scattering cell allows for measurements at gas pressures in the range 0−4 bars and at stably controlled temperatures from −30 °C to 70 °C. A scannable Fabry-Perot analyzer with instrument resolution of 232 MHz probes the RB profiles. Measurements on N2 and SF6 gases demonstrate that the high signal-to-noise ratio is achievable with the instrument at the 1% level at the peak amplitude of the scattering profile.
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07.60.Rd Visible and ultraviolet spectrometers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Simultaneous measurement of refractive index and temperature by integrating an external Fabry-Perot cavity with a fiber Bragg grating

Luan Xiong Chen, Xu Guang Huang, Jiao Yang Li, and Ze Bing Zhong

Rev. Sci. Instrum. 83, 053113 (2012); http://dx.doi.org/10.1063/1.4721274 (4 pages)

Online Publication Date: 29 May 2012

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A fiber sensor for simultaneous measurements of refractive index and temperature based on the integration of a fiber Bragg grating (FBG) with an external Fabry-Perot (F-P) cavity is presented. The fringe contrast of the interference spectrum generated by the F-P cavity is used to determine the external refractive index, while the wavelength shift of the FBG is used to measure temperature. The result showed that the refractive index and temperature sensitivity for the integrated sensor is 8.1 × 10−6 and 0.01006 nm/°C, respectively.
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42.81.Pa Sensors, gyros
07.20.Dt Thermometers
07.60.Hv Refractometers and reflectometers

Geometrical factor correction in grazing incident x-ray fluorescence experiment

Wenbin LI, Jingtao Zhu, Xiaoying Ma, Haochuan LI, Hongchang Wang, Kawal J. S. Sawhney, and Zhanshan Wang

Rev. Sci. Instrum. 83, 053114 (2012); http://dx.doi.org/10.1063/1.4722495 (5 pages)

Online Publication Date: 29 May 2012

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The geometrical factor in the grazing incident x-ray fluorescence analysis is an important angle-dependent term, which can have a great effect on the measured data. In this paper, the effects of the geometrical factor on the florescence yield have been demonstrated. A formula is presented to estimate the geometrical factor, which includes the experimental parameters of the beam and setup. The validity of this formula is proven by the good agreement between the calculated fluorescence yields with the experimental results in grazing incident x-ray fluorescence analysis.
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82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Noniterative algorithm for improving the accuracy of a multicolor-light-emitting-diode-based colorimeter

Pao-Keng Yang

Rev. Sci. Instrum. 83, 053115 (2012); http://dx.doi.org/10.1063/1.4723826 (5 pages)

Online Publication Date: 31 May 2012

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We present a noniterative algorithm to reliably reconstruct the spectral reflectance from discrete reflectance values measured by using multicolor light emitting diodes (LEDs) as probing light sources. The proposed algorithm estimates the spectral reflectance by a linear combination of product functions of the detector's responsivity function and the LEDs’ line-shape functions. After introducing suitable correction, the resulting spectral reflectance was found to be free from the spectral-broadening effect due to the finite bandwidth of LED. We analyzed the data for a real sample and found that spectral reflectance with enhanced resolution gives a more accurate prediction in the color measurement.
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85.60.Jb Light-emitting devices
07.60.Dq Photometers, radiometers, and colorimeters
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