Ultrasensitive Detectors Research Articles

Ultrasensitive-hot-electron microbolometer

We present measurements on a novel power detector which can be used as an ultrasensitive detector of millimeter and submillimeter radiation. The absorbing element consists of a thin film resistor strip which is connected to superconducting electrodes. This device exploits the Andreev reflection of electrons and the weak electron-phonon coupling at low temperatures to produce a large temperature rise for a small input power (≊10 mK/fW). The temperature rise of the electrons is detected by a tunnel junction where part of the metal strip forms the normal electrode. We have measured a voltage responsivity of approximately 109 V/W and an amplifier-limited electrical noise equivalent power ≊3×10−18 W Hz−1/2 at an operating temperature of 100 mK. If infrared radiation were efficiently coupled to the absorbing element with an antenna or a waveguide, then the sensitivity of this detector would be at least a factor of 10 better than the best available direct detector operating at the same temperature.

First observation of the quasibound levels and tunneling line broadening in the 3 1Πg state of Na2 using an ultrasensitive ionization detector

All quasibound vibrational energy levels v=27 and 28 of the Na2 3 1Πg state were accessed by using optical–optical double resonance and detected with a shielded ionization detector. The line broadening due to the tunneling effect was observed to be larger than 1 cm−1 at the rovibrational level v=28, J=31. The potential curve has been determined by the Rydberg–Klein–Rees method and modified using Jeung’s calculation for the large distance barrier and comparison of the calculated and the measured line widths. The barrier height was found to be ∼126 cm−1 above its asymptotic limit (3s+4p) at 5.98 Å. There also exists an unobserved shallow outer well with depth ∼35 cm−1 at 9.5 Å according to our modification of Jeung’s calculated potential. One way to possibly probe this outer well is also discussed.

Ultra-high velocity impacts: cratering studies of microscopic impacts from 3 km/s to 30 km/s

Cratering experiments performed under carefully controlled conditions at impact velocities ranging from 3 km/s to 30 km/s into a wide variety of target materials are presented. These impact experiments use the 6 MV vertical Van de Graaff accelerator of the Ion Beam Facility at the Los Alamos National Laboratory to electrostatically accelerate highly charged iron micro-spheres. The sub-micron spheres, from a random size distribution, are shocklessly accelerated along an 8 m flight path. Ultra-sensitive charge detectors monitor the passage of the projectiles at a rate of up to 100 projectiles/second. An online computer records and displays in real time the charge, velocity and mass of the projectiles and provides cross correlation between the events observed by the several in-flight charge detectors and impact detectors. Real-time logic controls an electrostatic kicker which deflects projectiles of selected charge and velocity onto the target. Thus each experiment consists of an ensemble of 10 to 40 impacts onto a single target within a narrow window of the projectile parameter space, providing excellent statistical resolution of each data point. The target materials used include single crystal copper and single crystal aluminum, gold, and quartz as well as pyrolytic graphic and anoxy used in composite materials of interest to space applications. We also conducted impact experiments onto thin Mylar and nickel foils. This paper presents these experiments and summarizes the cratering characterization performed to date. Emphasis is placed on cratering results in several materials over a range of impact velocities.

Terpenes in a conifer forest: Detection at sub-parts per billion level without sample preconcentration

Abstract In a natural atmosphere free from anthropogenic emissions, terpenes constitute a major part of the biogenic hydrocarbon family. The study of their involvement in chemical reactions with various oxidants in the atmosphere requires continuous and accurate checking of their diurnal concentration variations. In past studies, the ever present sample preconcentration step with large sample volumes is expected to be associated with the problems of sample loss or chemical modifications in addition to their limitations on the measurement frequency. To improve upon these drawbacks, a commercially available microprocessor-based portable gas chromatograph with an ultra-sensitive detector was successfully tested and used for in situ measurements. With a direct sample volume of a few hundred microlitres of ambient air and suitable selection of the column packing material, quick separation of the various components was achieved. Excellent operational features and on-line calibration with pure samples allowed accurate and instant measurements during field studies. The photoionization (PI) detector allowed high S/N ratio even at sub-parts per billion level concentration of the hydrocarbons. Data collected over a one-year period under varying meteorological conditions from a conifer forest situated at Gulmarg (34°03′N, 74°24′E, 2650 m MSL) indicates the suitability of this system for remote field studies and also throws light on the lifecycle of these hydrocarbons in the natural atmosphere. The different hydrocarbons measured in this evaluation study includes isoprene, α-pinene and β-pinene.

Innovations in helium leak detector systems

Innovations in helium leak detection systems have made it possible to detect leaks many decades smaller than previously thought existed. Several units of ultrasensitive leak detectors are routinely detecting leaks as small as 1 × 10−15 atm cc He/s. These ultrasensitive leak detectors are proving their worth in the quality control of infrared imaging sensor Dewars and in determining ultrahigh vacuum (UHV) performance characteristics of prototype hardware. Other innovations enable measurement of both gross leaks and fine leaks of microelectronics packages. A large leak from a 0.015-in.-diam hole in a 0.25-cc device as well as fine leaks down to 1 × 10−12 atm cc He/s were measured using this system. Because only one test is required for the gross and fine leaks, the cost of evaluating the hermaticity of the device is reduced. Included in this paper are the design concepts, operational modes, calibration methods, and test results.

Pulsed operation of a superconductive electromagnetic gradiometer

An electromagnetic gradiometer (EMG) combines a superconducting quantum interference device (SQUID) gradiometer with an active magnetic source for use as an ultrasensitive metal detector. A report on performance tests of an EMG configuration using a pulsed source is presented. Eddy currents persist in metallic targets between pulses and thus make them visible to the receiver. Because the receiver only looks between pulses, when the source is off, it is immune to noise from source interference. Performance tests validate an analytical model that predicts a detection range of 20 m to a target 25 cm in radius for a prototype pulsed EMG producing pulses 10-ms long separated by 10-ms intervals, with a peak moment of 2*10/sup 4/ A-m/sup 2/.

Quantum tunnelling of magnetisation

At IBM Research Laboratories in Yorktown Heights, NY, David Awschalom and co-workers are now able to study the magnetic properties of a single particle of magnetic material in the shape of a cylinder only 150 Å in diameter and 300 Å in length. They make use of an integrated DC SQUID microsusceptometer (1988 Appl. Phys. Lett. 53 2108), shown in figure 1, which is capable of detecting the magnetic field produced by the mere one million electron spins contained in the particle. The energy sensitivity of the instrument is very near the quantum limit set by the uncertainty principle, namely h divided by the time interval of observation (this is equal to the inverse frequency bandwidth). This accomplishment represents another great feat in the area of ultra-sensitive detectors and miniature sample preparation.

Thermal lens-circular dichroism detector for high-performance liquid chromatography

A novel and ultrasensitive chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents by the thermal lens effect. In this instrument, the chromatographic effluent was sequentially excited by left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams were derived from the same argon ion laser whose linearly polarized output was transformed into circularly polarized light by means of a Pockels cell. The heat generated as a consequence of the sample absorption of the LCPL and RCPL was measured by the probe laser beam collinearly overlapping with the two excitation beams. A lock-in amplifier was used to measure the thermal lens-circular dichroism (TL-CD) signal which corresponds to the difference in the thermal lens signals produced by the LCPL and RCPL excitation beams. In addition to its high sensitivity, the advantages of this TL-CD chiral detector include its ability to provide, directly and in real time, information on the chirality (i.e., circular dichroism) and optical purity of chiral samples. A detection limit of 7.2 ng was achieved for (-)-tris(ethylenediamine)cobalt(III) (k' = 0.45) as well as for the (+)-tris(ethylenediamine)cobalt(III) (k' = 1.40) when these two enantiomers were chromatographically separated from the corresponding racemic mixture through the use of bis(mu-d-tartrato)diantiomonate(III) ion pair reversed-phase chromatography. This limit of detection was found by using a 10-microL flow cell and having 5-mm path length and 6-mW excitation laser beam (lambda = 514.5 nm) modulated at 2 Hz.

Refractive index detector using Zeeman interferometry

We discuss the theory and error analysis for an ultrasensitive refractive index detector based on the two frequency Zeeman effect laser. Experimental measurements on gases agree fairly well with predictions. With a 5-cm pathlength, the typical interferometry stability is Deltan = 8 x 10(-9)/h. Resolution is Deltan = 1 x 10(-9).

Spectral properties of selected superconducting materials

Introduction D the 1960s, low-temperature superconducting materials were developed for specialized applications such as ultrasensitive magnetic field detectors. With the development of high-temperature superconductors, other applications not previously feasible have become much more attractive. These applications include electronic switching devices and the use of superconductors for radiation shielding. Because of the so-called Meisner effect in which magnetic fields are excluded, high-temperature superconducting materials may be suitable for aerospace applications requiring very low-emittance or switchable-emittance properties. Lowemittance applications include enhanced thermal isolation required for cryogenic devices and systems, whereas switchable properties are desirable for variable conductance devices and for optical signature control. As a consequence, high-temperature superconducting materials could be used as thin films to minimize weight and provide the rapid transient response so important in the application of switchable properties. Although there have been numerous investigations of lowtemperature superconducting materials, only limited data have been found for the thermophysical properties of the more recently developed high-temperature superconductors. There have been several investigations involving selected properties of high-temperature superconductors' including both thermal and electrical properties. However, the radiation properties of these materials have generally not been included in the reported literature. Tajima et al. reported some spectral reflectance data for compounds of

Ballistic phonon mediated detection of elementary particles in silicon

When an incident particle collides with an electron or nucleus in a silicon crystal, 70% of the recoil energy is converted into a burst of low-energy phonons. These phonons propagate ballistically for distances of several centimeters if the crystal has very few defects or impurities and if it is cooled to a temperature well below 1 K. Direct sensing of the phonons is the basis for a new type of elementary particle detector, called a silicon crystal acoustic detector (SiCAD), which will be used in neutrino experiments and in the search for other weakly interacting particles. The first generation of ultrasensitive phonon detectors consists of a thin film strip of a superconducting material, which is current biased just below the critical temperature. Incident phonons drive a segment of the film normal and thereby produce a voltage pulse. These devices have sufficient sensitivity and resolution to detect energy depositions of several keV in standard 3-in. silicon wafers. Research currently is in progress on the next generation of phonon detectors that will make use of superconducting tunnel junctions. [Work supported by DOE, NSF, and Research Corporation.]

CO2 Laser for Otosclerosis

Safe energy parameters for each Sharplan CO2 laser model (734, 1040, 1100A) were established in the laboratory. Ultrasensitive pyroelectric detectors analyzed the precise energy package delivered to the operative field with each of these power setting. Subsequently, 0.6-mm stapedotomy and stapedectomy revisions were performed under simulated operating room conditions while measuring temperature changes in the vestibule with a thermocouple. Table I illustrates safe energy settings for each of the Sharplan CO2 models tested. These power settings produced no more than 0.3 degrees C temperature rise in the vestibule during stapedotomy, and no more than 0.5 degrees C during stapedectomy revision. Following these guidelines, the CO2 laser was then employed to perform stapedotomy and stapedectomy revisions in otosclerosis patients. In over 200 consecutive operations performed under local anesthesia with the CO2 laser, no patient became dizzy intraoperatively while the CO2 laser was applied to the stapes footplate or the oval window neomembrane, confirming the lack of significant caloric effect to the inner ear at these energy settings. More importantly, no patient has yet experienced significant sensorineural hearing loss in the speech range.

The Impact of High-Temperature Superconductivity on SQUID Magnetometers

DC and RF Superconducting QUantum Interference Devices (SQUIDs) fabricated from low transition temperature (T(c)) superconductors and operated at liquid (4)He temperatures are routinely used as ultrasensitive detectors in many applications, for example, as magnetometers, magnetic gradiometers, voltmeters, and motion detectors. SQUIDs fabricated from high T(c) superconductors such as YBa(2)Cu(3)O(7) and operated in liquid nitrogen at 77 K offer a greater convenience in operation at the expense of a poorer noise performance, particularly at low frequencies. The resolution of SQUID-based magnetometers is compared with that of other types of magnetometers operatng at ambient temperatures.

Ballistic Quasiparticle Generation and Propagation in Superfluid 3He–B

Ballistic quasiparticles are produced by means of a supercritically driven wire resonator in 3He-B at temperatures below 0.25 TC. At 0 bar pressure the observed critical velocity of the wire is about 9 mm/s relative to the container (or about 18 mm/s relative to the maximum superfluid back flow). This velocity scales with (Δ/pF) as a function of pressure, confirming that pair-breaking of the superfluid is the dissipation mechanism. At higher temperatures, the scattering of existing quasiparticles leads to dissipation at much lower velocities. The ballistic propagation of a pulse of quasiparticles through the superfluid is demonstrated by the mechanical force it applies to a second wire resonator at a distance of up to 6 mm. The detector is incorporated into a SQUID circuit to yield an ultra-sensitive force detector. We observe strong signals at the detector at the same frequency as the power dissipation in the generating wire, and of a magnitude proportional to the power dissipation. The order of magnitude of these signals agrees with a simple theoretical model of ballistic quasiparticle propagation. Comparison of the received forces from a number of different driving wires suggests that the quasiparticles are emitted with almost cylindrical symmetry, with a low flux emitted parallel to the wire axis. The phase of the received signals at 0 bar indicates that the propagation is rapid. The small reduction in signal as the temperature is raised shows that the attenuation of the quasiparticle beam is low. Future experiments are proposed on the influence of Andreev scattering of quasiparticles from a super flow field.

Photoconductive Detectors Employing An Optically Induced Nonlinear Resistance

A new mode of operation of photoconductive detectors in which a nonlinear current-voltage characteristic is induced by illumination is described. Outputs at harmonic frequencies can be obtained from devices biased with alternating current or at the modulation frequency of a modulated, alternating bias. Several different ways to achieve the nonlinearity are described, one of which uses conventional detector structures. The advantages of this mode of operation are that the large bias-voltage pedestal, normally associated with long-wavelength photoconductive detectors, can be separated from the photo-signal by simple electrical filters and that the problem of flicker noise, in both the detector and the following electronics, is considerably reduced. Photoconductive devices thus become competitive with photodiodes, which may be more difficult to produce with ideal performance and stable characteristics, in detect-ing radiation with very low modulation frequencies. Possible applications for the device may be in slow, parallel-scanned linear arrays; in staring arrays; in ultrasensitive detectors employing long integration times; and in position-sensitive, point-source detectors.

Ultrasensitive measuring devices

Abstract Both dc and rf Superconducting QUantum Interference Devices (SQUIDs) are widely used as ultrasensitive detectors of magnetic flux. Present research is focussed largely on thin-film dc SQUIDs fabricated with photolithographic techniques. The current status of this field is briefly reviewed. The impact of dc SQUIDs with improved sensitivity on noise thermometry and gravitational wave antennas is discussed.

Superconductive tunneling devices as millimeter wave photon detectors

A quantum generalization of microwave mixer theory predicts that superconductive tunneling devices may be employed as ultrasensitive low noise photon detectors at millimeter wave frequencies.

Trace gas analysis by a new high sensitivity thermal conductivity detector

Inorganic gas analysis at the sub-ppm level requires preconcen-tration or the use of an ultrasensitive Helium detector. There are several problems with both methods if precise determinations are required. Until now, it has not been possible to use a hot-wire thermal conductivity detector for the purpose owing to its lack of sensitivity. A new TCD-system, which achieves major improvements in filament protection and in sensitivity, has been developed. The high sensitivity required for trace gas analysis has been obtained through the combination of a small-volume TC-cell, reduction of noise to a very low level and use of a built-in output-signal amplifier. Filament protection has been realized by operating the cell at constant mean temperature, and by using two electronic circuits for power cut-off when there is no carrier gas flow through the detector. With the addition of a single printed circuit card to the TCD-controller module, the detector is capable of automatic operation in conjunction with the microprocessor-controlled Varian Chromatography Data System CDS-111. Automatic operation includes auto-zeroing, auto-ranging and monitoring of the TCD. For calibration of the detector the inexpensive exponential dilution flask method was used, because commercial standards were usually either unreliable or expensive. The following concentrations were the minimum detectable with a relatively cool filament (300· C) and helium as carrier gas: argon, methane 0.1 ppm; oxygen, carbon monoxide, carbon dioxide, ethylene, acetylene 0.2 ppm; nitrogen 0.3 ppm; hydrogen 5 ppm. With nitrogen as carrier gas 0.3 ppm of hydrogen could be detected. These results can only be achieved after very careful checking and elimination of all leaks in the system. The application of such a sensitive, constant-temperature, amplified thermoconductivity detector should be of advantage for gas analysis at the sub-ppm level, which could formerly only be done with ultrasensitive but expensive helium detectors.

An ultrasensitive hydrogen detector and its applications: K B Das, J Vac Sci Technol, 11 (2), 1974, 498–505

An ultrasensitive hydrogen detector and its applications: K B Das, J Vac Sci Technol, 11 (2), 1974, 498–505

An ultrasensitive hydrogen detector and its applications

An ultrasensitive hydrogen detector is described which has a detection sensitivity of a few parts per billion in the gas stream. The detector's performance, range, and accuracy were evaluated by analyzing titanium standards from NBS containing known amounts of hydrogen at the following levels: 32±5, 98±5, and 215±6 ppm. The fractional random error in the mean value of these standards at 95% confidence level was found to be ±5.01%, ±1.67%, and ±1.08%, respectively. The detector has been used on surface contamination, corrosion, hydrogen concentration gradient, and hydrogen embrittlement studies. When two such detectors are connected in a Y configuration, the system becomes a vacuum gauge calibrator which does not involve a flowmeter. The principle of operation and highlights of the above studies are presented along with the sensitivity factor for a Bayard–Alpert-type ionization gauge for hydrogen gas.