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Oct 2007

Volume 78, Issue 10, Articles (10xxxx)

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Digitally balanced detection for optical tomography

Rehan Hafiz and Krikor B. Ozanyan

Rev. Sci. Instrum. 78, 103101 (2007); http://dx.doi.org/10.1063/1.2793506 (9 pages) | Cited 3 times

Online Publication Date: 3 October 2007

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Analog balanced Photodetection has found extensive usage for sensing of a weak absorption signal buried in laser intensity noise. This paper proposes schemes for compact, affordable, and flexible digital implementation of the already established analog balanced detection, as part of a multichannel digital tomography system. Variants of digitally balanced detection (DBD) schemes, suitable for weak signals on a largely varying background or weakly varying envelopes of high frequency carrier waves, are introduced analytically and elaborated in terms of algorithmic and hardware flow. The DBD algorithms are implemented on a low-cost general purpose reconfigurable hardware (field-programmable gate array), utilizing less than half of its resources. The performance of the DBD schemes compare favorably with their analog counterpart: A common mode rejection ratio of 50 dB was observed over a bandwidth of 300 kHz, limited mainly by the host digital hardware. The close relationship between the DBD outputs and those of known analog balancing circuits is discussed in principle and shown experimentally in the example case of propane gas detection.
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42.30.Wb Image reconstruction; tomography

A narrow-band injection-seeded pulsed titanium:sapphire oscillator-amplifier system with on-line chirp analysis for high-resolution spectroscopy

S. Hannemann, E.-J. van Duijn, and W. Ubachs

Rev. Sci. Instrum. 78, 103102 (2007); http://dx.doi.org/10.1063/1.2789690 (9 pages) | Cited 6 times

Online Publication Date: 4 October 2007

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A narrow-band tunable injection-seeded pulsed titanium:sapphire laser system has been developed for application in high-resolution spectroscopic studies at the fundamental wavelengths in the near infrared as well as in the ultraviolet, deep ultraviolet, and extreme ultraviolet after upconversion. Special focus is on the quantitative assessment of the frequency characteristics of the oscillator-amplifier system on a pulse-to-pulse basis. Frequency offsets between continuous-wave seed light and the pulsed output are measured as well as linear chirps attributed mainly to mode pulling effects in the oscillator cavity. Operational conditions of the laser are found in which these offset and chirp effects are minimal. Absolute frequency calibration at the megahertz level of accuracy is demonstrated on various atomic and molecular resonance lines.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Fc Modulation, tuning, and mode locking
42.62.Fi Laser spectroscopy
42.70.Hj Laser materials

Performance trade-offs in single-photon avalanche diode miniaturization

Hod Finkelstein, Mark J. Hsu, Sanja Zlatanovic, and Sadik Esener

Rev. Sci. Instrum. 78, 103103 (2007); http://dx.doi.org/10.1063/1.2796146 (5 pages) | Cited 9 times

Online Publication Date: 12 October 2007

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Single-photon avalanche diodes (SPADs) provide photons’ time of arrival for various applications. In recent years, attempts have been made to miniaturize SPADs in order to facilitate large-array integration and in order to reduce the dead time of the device. We investigate the benefits and drawbacks of device miniaturization by characterizing a new fast SPAD in a commercial 0.18 μm complementary metal oxide semiconductor technology. The device employs a novel and efficient guard ring, resulting in a high fill factor. Thanks to its small size, the dead time is only 5 ns, resulting in the fastest reported SPAD to date. However, the short dead time is accompanied by a high after-pulsing rate, which we show to be a limiting parameter for SPAD miniaturization. We describe a new and compact active-recharge scheme which improves signal-to-noise tenfold compared with the passive configuration, using a fraction of the area of state-of-the-art active-recharge circuits, and without increasing the dead time. The performance of compact SPADs stands to benefit such applications as high-resolution fluorescence-lifetime imaging, active-illumination three-dimensional imagers, and quantum key distribution systems.
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85.60.Dw Photodiodes; phototransistors; photoresistors
42.79.Pw Imaging detectors and sensors
85.30.Tv Field effect devices

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum

Jens Steidtner and Bruno Pettinger

Rev. Sci. Instrum. 78, 103104 (2007); http://dx.doi.org/10.1063/1.2794227 (8 pages) | Cited 32 times

Online Publication Date: 15 October 2007

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An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of ∼ 106 and a net signal gain of up to 4000 was observed. The focus diameter ( ∼ λ/2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.
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07.79.Cz Scanning tunneling microscopes
07.30.-t Vacuum apparatus
78.30.Hv Other nonmetallic inorganics
78.30.Jw Organic compounds, polymers

An accurate, repeatable, and well characterized measurement of laser damage density of optical materials

L. Lamaignère, S. Bouillet, R. Courchinoux, T. Donval, M. Josse, J.-C. Poncetta, and H. Bercegol

Rev. Sci. Instrum. 78, 103105 (2007); http://dx.doi.org/10.1063/1.2796148 (9 pages) | Cited 22 times

Online Publication Date: 16 October 2007

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Known for more than 40 years, laser damage phenomena have not been measured reproducibly up to now. Laser resistance of optical components is decreased by the presence of material defects, the distribution of which can initiate a distribution of damage sites. A raster scan test procedure has been used for several years in order to determine laser damage density of large aperture UV fused silica optics. This procedure was improved in terms of accuracy and repeatability. We describe the equipment, test procedure, and data analysis to perform this damage test of large aperture optics with small beams. The originality of the refined procedure is that a shot to shot correlation is performed between the damage occurrence and the corresponding fluence by recording beam parameters of hundreds of thousands of shots during the test at 10 Hz. We characterize the distribution of damaging defects by the fluence at which they cause damage. Because tests are realized with small Gaussian beams (about 1 mm at 1/e), beam overlap and beam shape are two key parameters which have to be taken into account in order to determine damage density. After complete data analysis and treatment, we reached a repeatable metrology of laser damage performance. The measurement is destructive for the sample. However, the consideration of error bars on defect distributions in a series of parts allows us to compare data with other installations. This will permit to look for reproducibility, a necessary condition in order to test theoretical predictions.
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42.79.Ag Apertures, collimators
42.87.-d Optical testing techniques
42.88.+h Environmental and radiation effects on optical elements, devices, and systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.-a Optical materials

Kilohertz laser ablation for doping helium nanodroplets

M. Mudrich, B. Forkl, S. Müller, M. Dvorak, O. Bünermann, and F. Stienkemeier

Rev. Sci. Instrum. 78, 103106 (2007); http://dx.doi.org/10.1063/1.2796849 (8 pages) | Cited 2 times

Online Publication Date: 23 October 2007

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A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the nonvolatile DNA basis guanine is found to be efficient and a number of oligomers are detected.
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61.72.up Other materials
52.38.Mf Laser ablation

An attenuated total reflectance far-UV spectrometer

Noboru Higashi, Akifumi Ikehata, and Yukihiro Ozaki

Rev. Sci. Instrum. 78, 103107 (2007); http://dx.doi.org/10.1063/1.2796928 (5 pages) | Cited 10 times

Online Publication Date: 26 October 2007

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An ultraviolet spectrometer based on attenuated total reflection (ATR) has been developed and tested for liquid water (light and heavy water) in the wavelength range from 140 to 300 nm, which includes the far ultraviolet (FUV) region. One of the principal limitations of FUV transmission spectra is the strong absorption of the solvent itself. High absorptivity of the n→σ* transition in water molecule has thus far prevented meaningful spectral measurements of aqueous solutions in the wavelength region under 170 nm. Our technique uses the evanescent wave created through total reflection when light is passed through an internal reflection element (IRE) in contact with the sample. Since the evanescent field is used as an optical path length, the method allows spectral measurements favorably comparable with that of transmittance method with a shorter path length than the wavelength of FUV light. In this study, we have designed an original miniature IRE probe made of sapphire that allows detection of the whole n→σ* transition absorption band of water down to 140 nm. The obtained ATR-FUV spectra closely match calculations based on the Fresnel formula. It is also confirmed that this spectrometer is equally effective for spectral measurements of nonaqueous solvents with significant absorptivities in the FUV region.
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07.60.Rd Visible and ultraviolet spectrometers

High-time-resolution pump-probe system with broadband detection for the study of time-domain vibrational dynamics

Dario Polli, Larry Lüer, and Giulio Cerullo

Rev. Sci. Instrum. 78, 103108 (2007); http://dx.doi.org/10.1063/1.2800778 (9 pages) | Cited 45 times

Online Publication Date: 29 October 2007

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We present an ultrafast transient absorption spectroscopy system in the visible combining high-sensitivity broadband detection with extreme temporal resolution. The instrument is based on an ultrabroadband sub-10 fs optical parametric amplifier coupled to an optical multichannel analyzer with fast electronics, enabling single-shot detection at 1 kHz repetition rate. For a given pump-probe delay τ, we achieve a differential transmission (ΔT/T) sensitivity of the order of 10−4 over the λpr = 490–720 nm probe wavelength range by averaging over 1000 shots, allowing the acquisition of complete two-dimensional ΔT/T (λpr,τ) maps within a few minute measurement time. We present application examples highlighting the capability of this instrument to observe ultrafast dynamical processes, follow impulsively excited vibrational motions with frequency as high as 3000 cm−1 (11 fs period), and determine the probe wavelength dependence of amplitude and phase of the oscillations.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Yj Optical parametric oscillators and amplifiers

An electrostatic glass actuator for ultrahigh vacuum: A rotating light trap for continuous beams of laser-cooled atoms

F. Füzesi, A. Jornod, P. Thomann, M. D. Plimmer, G. Dudle, R. Moser, L. Sache, and H. Bleuler

Rev. Sci. Instrum. 78, 103109 (2007); http://dx.doi.org/10.1063/1.2800777 (9 pages)

Online Publication Date: 31 October 2007

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This article describes the design, characterization, and performance of an electrostatic glass actuator adapted to an ultrahigh vacuum environment (10−8 mbar). The three-phase rotary motor is used to drive a turbine that acts as a velocity-selective light trap for a slow continuous beam of laser-cooled atoms. This simple, compact, and nonmagnetic device should find applications in the realm of time and frequency metrology, as well as in other areas of atomic, molecular physics and elsewhere.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
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Laser output power stabilization for direct laser writing system by using an acousto-optic modulator

Dong Ik Kim, Hyug-Gyo Rhee, Jae-Bong Song, and Yun-Woo Lee

Rev. Sci. Instrum. 78, 103110 (2007); http://dx.doi.org/10.1063/1.2801012 (4 pages) | Cited 2 times

Online Publication Date: 31 October 2007

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We present experimental results on the output power stabilization of an Ar+ laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of ±0.20% for 12 min and the relative intensity noise level of 2.1×10−7 Hz−1/2 at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He–Ne laser. As a consequence, we achieved the output power stability of ±0.12% for 25 min.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Jq Acousto-optical devices
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A ground-based radio frequency inductively coupled plasma apparatus for atomic oxygen simulation in low Earth orbit

Yongxian Huang, Xiubo Tian, Shiqin Yang, and Paul K. Chu

Rev. Sci. Instrum. 78, 103301 (2007); http://dx.doi.org/10.1063/1.2800766 (4 pages) | Cited 2 times

Online Publication Date: 25 October 2007

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A radio frequency (rf) inductively coupled plasma apparatus has been developed to simulate the atomic oxygen environment encountered in low Earth orbit (LEO). Basing on the novel design, the apparatus can achieve stable, long lasting operation, pure and high density oxygen plasma beam. Furthermore, the effective atomic oxygen flux can be regulated. The equivalent effective atomic oxygen flux may reach (2.289–2.984)×1016 at./cm2 s at an oxygen pressure of 1.5 Pa and rf power of 400 W. The equivalent atomic oxygen flux is about 100 times than that in the LEO environment. The mass loss measured from the polyimide sample changes linearly with the exposure time, while the density of the eroded holes becomes smaller. The erosion mechanism of the polymeric materials by atomic oxygen is complex and involves initial reactions at the gas-surface interface as well as steady-state material removal.
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81.65.-b Surface treatments
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)

A compact high power pulsed modulator based on spiral Blumlein line

Jinliang Liu, Yi Yin, Bin Ge, Xinbing Cheng, Jiahuai Feng, Jiande Zhang, and Xinxin Wang

Rev. Sci. Instrum. 78, 103302 (2007); http://dx.doi.org/10.1063/1.2800751 (5 pages) | Cited 16 times

Online Publication Date: 26 October 2007

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A compact high power pulsed modulator based on spiral water Blumlein line, which consists of primary storage capacitors, a Tesla transformer, a spiral Blumlein line of water dielectric, and a field-emission diode, is described. The experimental results showed that the diode voltage is more than 500 kV, the electron beam current of diode is about 32 kA, and the pulse duration is about 180 ns. The distributions for electrical field in the spiral water Blumlein line were obtained by the simulations. In addition, the process of the charging a spiral Blumlein line was simulated through the PSPICE software to get the wave form of charging voltage of pulse forming line, the diode voltage, and diode current of modulator. The theoretical and simulated results are in agreement. This accelerator is very compact and works stably and reliably.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.30.Bv Circuit theory

Mass and position determination of attached particles on cantilever based mass sensors

S. Dohn, W. Svendsen, A. Boisen, and O. Hansen

Rev. Sci. Instrum. 78, 103303 (2007); http://dx.doi.org/10.1063/1.2804074 (3 pages) | Cited 32 times

Online Publication Date: 31 October 2007

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An analytical expression relating mass and position of a particle attached on a cantilever to the resulting change in cantilever resonant frequency is derived. Theoretically, the position and mass of the attached particle can be deduced by combining measured resonant frequencies of several bending modes. This finding is verified experimentally using a microscale cantilever with and without an attached gold bead. The resonant frequencies of several bending modes are measured as a function of the bead position. The bead mass and position calculated from the measured resonant frequencies are in good agreement with the expected mass and the position measured.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Changes of optical properties of retroreflector installed in LHD

T. Akiyama, K. Kawahata, N. Ashikawa, M. Tokitani, S. Okajima, K. Nakayama, N. Yoshida, A. Ebihara, K. Tokunaga, Y. Ohtawa, and S. Tsuji-Iio

Rev. Sci. Instrum. 78, 103501 (2007); http://dx.doi.org/10.1063/1.2786938 (7 pages) | Cited 5 times

Online Publication Date: 3 October 2007

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This article describes changes of optical properties of retroreflectors installed on the inner wall of the vacuum vessel of the Large Helical Device. They were made of stainless steel and were used for a CO2 laser polarimeter. The reflectivity for a CO2 laser beam dropped up to 40% after the start of glow discharge cleanings and main plasma experiments. Then it decreased gradually. The reflectivity in a wavelength range shorter than 10 μm decreased significantly through one experimental campaign (about 4 months). On the other hand the reflectivity in a wavelength range longer than 50 μm was larger than 70%. Decrease in the reflectivity in the central region of mirrors was more significant (the reflectivity for visible beams became almost zero) than that in the edge. The distribution of the reflectivity along the radial direction is expected to be related to the shape of the retroreflector. The parallelism of the reflected beam to an incident one also deteriorated. The changes in the polarization angle and in the ellipticity of reflected light polarization were not observed from the visible to the far infrared range.
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42.79.Bh Lenses, prisms and mirrors
42.25.Gy Edge and boundary effects; reflection and refraction
42.15.Eq Optical system design
07.60.Fs Polarimeters and ellipsometers
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Jd Magnetic mirrors, gas dynamic traps

Efficient Kα x-ray source from submillijoule femtosecond laser pulses operated at kilohertz repetition rate

C. G. Serbanescu, J. A. Chakera, and R. Fedosejevs

Rev. Sci. Instrum. 78, 103502 (2007); http://dx.doi.org/10.1063/1.2789676 (6 pages) | Cited 10 times

Online Publication Date: 5 October 2007

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We report an efficient Cu Kα x-ray source produced by focusing submillijoule, 120 fs Ti:sapphire laser pulses on a solid copper target to a spot diameter of few microns. The experimental results show strong emission of Kα x-rays from solid targets from microplasmas created by p-polarized 0.2–0.3 mJ laser pulses at 1 kHz repetition rate. We have demonstrated Kα x-ray point source emission rates of 6.7×109 photons/s into 2π sr at 1 kHz repetition rate. The source has an x-ray conversion efficiency into Cu Kα line emission of 3.2×10−5. The source has a measured size of ∼ 8 μm. Such a high repetition rate Kα x-ray source can be very useful for time resolved x-ray diffraction and radiographic applications.
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52.50.Dg Plasma sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Ion beam capture and charge breeding in electron cyclotron resonance ion source plasmas

Jin-Soo Kim, L. Zhao, B. P. Cluggish, and Richard Pardo

Rev. Sci. Instrum. 78, 103503 (2007); http://dx.doi.org/10.1063/1.2785844 (9 pages) | Cited 1 time

Online Publication Date: 10 October 2007

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Beam capture of injected ions and charge breeding in electron cyclotron resonance (ECR) charge breeder ion source plasmas has been investigated utilizing an ECR plasma modeling code, the generalized ECR ion source model, and a Monte Carlo beam capture code. Beam capturing dynamics, charge breeding in the plasma, and the extracted charged ion states are described. Optimization of ion beam energy is performed for (1) high beam capture efficiency and (2) high charge state ion beam extractions. A sample case study for ANL-ECR has been performed. Ions entering ECR ion source plasma are slowed down mostly by the background ions. Assuming Maxwellian plasma ions, maximum beam energy loss occurs when the beam velocity is around the background thermal velocity in magnitude. It is also found that beam capture location affects charge state distribution. For instance, with a majority of beam ions captured near the middle of the device higher currents for higher charge states are obtained. The beam ions captured near the entry have a higher probability of backstreaming after they are captured. For this reason, the optimum beam energy of the injected Ar+ beam ions for charge breeding is generally higher than the optimum input beam energy for maximum beam energy loss.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
52.50.Dg Plasma sources
52.40.Mj Particle beam interactions in plasmas
52.65.Pp Monte Carlo methods

Data acquisition system for an advanced x-ray imaging crystal spectrometer using a segmented position-sensitive detector

U. W. Nam, S. G. Lee, J. G. Bak, M. K. Moon, J. K. Cheon, and C. H. Lee

Rev. Sci. Instrum. 78, 103504 (2007); http://dx.doi.org/10.1063/1.2795650 (4 pages) | Cited 3 times

Online Publication Date: 11 October 2007

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A versatile time-to-digital converter based data acquisition system for a segmented position-sensitive detector has been developed. This data acquisition system was successfully demonstrated to a two-segment position-sensitive detector. The data acquisition system will be developed further to support multisegmented position-sensitive detector to improve the photon count rate capability of the advanced x-ray imaging crystal spectrometer system.
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61.05.C- X-ray diffraction and scattering
07.05.Hd Data acquisition: hardware and software
07.85.Nc X-ray and γ-ray spectrometers

Honeycomblike large area LaB6 plasma source for Multi-Purpose Plasma facility

Hyun-Jong Woo, Kyu-Sun Chung, Hyun-Jong You, Myoung-Jae Lee, Taihyeop Lho, Kwon Kook Choh, Jung-Sik Yoon, Yong Ho Jung, Bongju Lee, Suk Jae Yoo, and Myeon Kwon

Rev. Sci. Instrum. 78, 103505 (2007); http://dx.doi.org/10.1063/1.2794705 (6 pages) | Cited 1 time

Online Publication Date: 15 October 2007

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A Multi-Purpose Plasma (MP2) facility has been renovated from Hanbit mirror device [ Kwon et al., Nucl. Fusion 43, 686 (2003) ] by adopting the same philosophy of diversified plasma simulator (DiPS) [ Chung et al., Contrib. Plasma Phys. 46, 354 (2006) ] by installing two plasma sources: LaB6 (dc) and helicon (rf) plasma sources; and making three distinct simulators: divertor plasma simulator, space propulsion simulator, and astrophysics simulator. During the first renovation stage, a honeycomblike large area LaB6 (HLA-LaB6) cathode was developed for the divertor plasma simulator to improve the resistance against the thermal shock fragility for large and high density plasma generation. A HLA-LaB6 cathode is composed of the one inner cathode with 4 in. diameter and the six outer cathodes with 2 in. diameter along with separate graphite heaters. The first plasma is generated with Ar gas and its properties are measured by the electric probes with various discharge currents and magnetic field configurations. Plasma density at the middle of central cell reaches up to 2.6×1012 cm−3, while the electron temperature remains around 3–3.5 eV at the low discharge current of less than 45 A, and the magnetic field intensity of 870 G. Unique features of electric property of heaters, plasma density profiles, is explained comparing with those of single LaB6 cathode with 4 in. diameter in DiPS.
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52.50.Dg Plasma sources
52.65.-y Plasma simulation
52.25.-b Plasma properties
52.50.-b Plasma production and heating
52.70.Ds Electric and magnetic measurements

Novel x-ray multispectral imaging of ultraintense laser plasmas by a single-photon charge coupled device based pinhole camera

L. Labate, A. Giulietti, D. Giulietti, P. Köster, T. Levato, L. A. Gizzi, F. Zamponi, A. Lübcke, T. Kämpfer, I. Uschmann, and E. Förster

Rev. Sci. Instrum. 78, 103506 (2007); http://dx.doi.org/10.1063/1.2800774 (6 pages) | Cited 7 times

Online Publication Date: 25 October 2007

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Spectrally resolved two-dimensional imaging of ultrashort laser-produced plasmas is described, obtained by means of an advanced technique. The technique has been tested with microplasmas produced by ultrashort relativistic laser pulses. The technique is based on the use of a pinhole camera equipped with a charge coupled device detector operating in the single-photon regime. The spectral resolution is about 150 eV in the 4–10 keV range, and images in any selected photon energy range have a spatial resolution of 5 μm. The potential of the technique to study fast electron propagation in ultraintense laser interaction with multilayer targets is discussed and some preliminary results are shown.
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07.85.-m X- and γ-ray instruments
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Rhodium coated mirrors deposited by magnetron sputtering for fusion applications

L. Marot, G. De Temmerman, P. Oelhafen, G. Covarel, and A. Litnovsky

Rev. Sci. Instrum. 78, 103507 (2007); http://dx.doi.org/10.1063/1.2800779 (7 pages) | Cited 15 times

Online Publication Date: 29 October 2007

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Metallic mirrors will be essential components of all optical spectroscopy and imaging systems for ITER plasma diagnostics. Any change in the mirror performance, in particular, its reflectivity, due to erosion of the surface by charge exchange neutrals or deposition of impurities will influence the quality and reliability of the detected signals. Due to its high reflectivity in the visible wavelength range and its low sputtering yield, rhodium appears as an attractive material for first mirrors in ITER. However, the very high price of the raw material calls for using it in the form of a film deposited onto metallic substrates. The development of a reliable technique for the preparation of high reflectivity rhodium films is therefore of the highest importance. Rhodium layers with thicknesses of up to 2 μm were produced on different substrates of interest (Mo, stainless steel, Cu) by magnetron sputtering. Produced films exhibit a low roughness and crystallite size of about 10 nm with a dense columnar structure. No impurities were detected on the surface after deposition. Scratch tests demonstrate that adhesion properties increase with substrate hardness. Detailed optical characterizations of Rh-coated mirrors as well as results of erosion tests performed both under laboratory conditions and in the TEXTOR tokamak are presented in this paper.
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81.65.Kn Corrosion protection
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.15.Cd Deposition by sputtering
68.35.Ct Interface structure and roughness
42.79.Bh Lenses, prisms and mirrors

A maximum-likelihood algorithm for reduction of Langmuir probe data

Adam K. Martin and Syri J. Koelfgen

Rev. Sci. Instrum. 78, 103508 (2007); http://dx.doi.org/10.1063/1.2801010 (6 pages)

Online Publication Date: 31 October 2007

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The reduction of Langmuir triple and quadruple probe data, i.e., the determination of the electron temperature Te from the measured voltages and currents, requires the solution of an implicit transcendental equation in Te, at every point in time. Random errors and noise in the measurements occasionally precludes solution of the equation, resulting in an indeterminate temperature at those times. We present a method for overcoming this problem that uses the method of maximum likelihood. The experimental uncertainties, assumed to be normally distributed, are used in solving the implicit equation in Te. At every point in time, a likelihood function is calculated, and the temperature which maximizes this function is taken to be the solution Te. The uncertainty in the resulting measurement is taken to be the width of the likelihood function. Examples of this technique are shown.
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52.70.Ds Electric and magnetic measurements

XUV laser-plasma source based on solid Ar filament

Christian Peth, Anton Kalinin, Frank Barkusky, Klaus Mann, J. Peter Toennies, and Lev Yu Rusin

Rev. Sci. Instrum. 78, 103509 (2007); http://dx.doi.org/10.1063/1.2801882 (6 pages) | Cited 4 times

Online Publication Date: 31 October 2007

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We present a laser driven soft x-ray source based on a novel solid argon filament. The continuously flowing micron-sized filament (diameter ∼ 56 μm, flow speed ∼ 5 mm/s) was used as a laser target in order to generate a plasma source of high brightness in the “water window” (2.2–4.4 nm) spectral range. The emission properties of the source were characterized in detail with respect to crucial parameters such as positional and energy stability using an extreme ultraviolet (XUV) sensitive pinhole camera and an XUV spectrometer. The results are compared with an argon plasma based on a gas puff target operated under the same experimental conditions showing an increase of the brilliance by a factor of 84. By changing the capillary geometry from a constant diameter to a convergent shape the flow speed of the filament was significantly increased up to 250 mm/s, facilitating the operation at higher repetition rates.
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52.50.Dg Plasma sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
07.85.Nc X-ray and γ-ray spectrometers
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An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging

Bogdan Diaconescu, Georgi Nenchev, Juan de la Figuera, and Karsten Pohl

Rev. Sci. Instrum. 78, 103701 (2007); http://dx.doi.org/10.1063/1.2789655 (6 pages) | Cited 6 times

Online Publication Date: 1 October 2007

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We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8×8 μm2. The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
07.10.Fq Vibration isolation
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

PFabrication of gold tips by chemical etching in aqua regia

F. Bonaccorso, G. Calogero, G. Di Marco, O. M. Maragò, P. G. Gucciardi, U. Giorgianni, K. Channon, and G. Sabatino

Rev. Sci. Instrum. 78, 103702 (2007); http://dx.doi.org/10.1063/1.2782682 (4 pages) | Cited 6 times

Online Publication Date: 3 October 2007

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We present a method to produce sharp gold tips for applications in apertureless near-field optical microscopy and spectroscopy. Thin gold wires are tapered by chemical etching in aqua regia, covered by an isooctane protective layer. Tips with apical radii of curvature of <50 nm are obtained with a 40% yield. The tip performances have been checked by shear-force imaging of amyloid fibrils samples and compared to optical fiber probes. The analysis of the tip morphology, carried out by scanning electron microscopy, shows the existence of two different etching processes occurring in bulk and at the liquid-liquid interface. A simple analytical model is presented to describe the dynamics of the tip formation at the liquid-liquid meniscus interface that fits remarkably well the experimental results in terms of tip shape and length.
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81.20.-n Methods of materials synthesis and materials processing
81.65.Cf Surface cleaning, etching, patterning

Suppression of spurious vibration of cantilever in atomic force microscopy by enhancement of bending rigidity of cantilever chip substrate

Toshihiro Tsuji, Kentaro Kobari, Seishiro Ide, and Kazushi Yamanaka

Rev. Sci. Instrum. 78, 103703 (2007); http://dx.doi.org/10.1063/1.2793498 (6 pages) | Cited 4 times

Online Publication Date: 5 October 2007

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To improve the precision of dynamic atomic force microscopy (AFM) using cantilever vibration spectra, a simple but effective method for suppressing spurious response (SR) was developed. The dominant origin of SR was identified to be the bending vibration of the cantilever substrate, by the analysis of the frequency of SR. Although a rigid cover pressing the whole surface of the substrate suppressed SR, the utility was insufficient. Then, a method of enhancing the bending rigidity of the substrate by gluing a rigid plate (clamping plate, CP) to the substrate was developed. This chip can be used with an ordinary cantilever holder, so that the reproducibility of SR suppression when attaching and detaching the cantilever chip to the holder was improved. To verify its utility, the evaluation of a microdevice electrode was performed by ultrasonic atomic force microscopy. The delamination at a submicron depth was visualized and the detailed variation of the delamination was evaluated for the first time using clear resonance spectra. The CP method will particularly contribute to improving dynamic-mode AFM, in which resonance spectra with a low quality factor are used, such as noncontact mode AFM in liquid or contact resonance mode AFM. The effect of the CP can be achieved by fabricating a substrate with a thick plate beforehand.
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07.79.Lh Atomic force microscopes
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