Cascade Detector Research Articles

16.5 μ m quantum cascade detector using miniband transport

The authors report on an InP based photovoltaic quantum cascade detector operating at 16.5μm and using miniband-based vertical transport. This concept allowed the construction of a longitudinal optical phonon extraction stair with two rungs without touching on a high device resistance. At 10K, they observed a responsivity of 1.72mA∕W and a Johnson noise limited detectivity of 2.2×109 Jones. Altogether, this design resulted in detection at temperatures of up to 90K with a lower bandwidth limit of 200MHz imposed by the measurement setup.

Electronic transport in quantum cascade structures at equilibrium

The transport in complex multiple quantum well heterostructures is theoretically described. The model is focused on quantum cascade detectors, which represent an exciting challenge due to the complexity of the structure containing 7 or 8 quantum wells of different widths. Electronic transport can be fully described without any adjustable parameter. Diffusion from one subband to another is calculated with a standard electron-optical phonon hamiltonian, and the electronic transport results from a parallel flow of electrons using all the possible paths through the different subbands. Finally, the resistance of such a complex device is given by a simple expression, with an excellent agreement with experimental results. This relation involves the sum of transitions rates between subbands, from one period of the device to the next one. This relation appears as an Einstein relation adapted to the case of complex multiple quantum structures.

A THz quantum cascade detector in a strong perpendicular magnetic field

A 3.6 THz quantum cascade detector is studied under the influence of a strong magnetic field applied perpendicularly to the plane of the layers. Modulation of lifetimes based on elastic intersubband scattering processes is observed, leading to an increase of the responsivity for particular values of the applied magnetic field.

23 GHz operation of a room temperature photovoltaic quantum cascade detector at 5.35μm

We present a room temperature operated 5.35μm quantum cascade detector which was tested at high frequencies using an optical heterodyne experiment. Two slightly detuned continuous wave distributed feedback single mode quantum cascade lasers were used to generate a beating signal. The maximum frequency at which the resulting microwave signal could be detected was 23GHz. The cutoff behavior of our device was modeled with a simple RLC circuit and showed excellent agreement with the experimental data.

Characterization of pore size of trimethylol propane triacrylate (TMPTA) polymer foam by pulsed sputter coating and SEM analysis

This paper describes the production and characterisation of low density polymeric foams used by the Atomic Weapons Establishment (AWE) Plasma Physics programme. Production and preparation of such foam samples for characterisation by scanning electron microscopy (SEM) are described. Examining non-conductive low density foam specimens by conventional SEM requires sputter coating with a very thin layer of gold to prevent overcharging the sample. This paper describes modifications to this process, which have illustrated the destructive effects of the sputtering process on these foams. Optimum conditions to minimise foam damage during sputtering have been determined. Low-vacuum SEM in conjunction with a charge cascade detector which enables non-conductive samples to be directly imaged has been used to reduce the damage to fragile foams. These results are compared with those taken of samples coated under optimum sputtering conditions. Using sputter coating time trials and an absorbed electron (AE) detector, it was revealed that the pore size of TMPTA foam was in the region of 0.1 μm, i.e. an order of magnitude lower than reported previously. Some proposed damage mechanisms are also discussed.

InP-based quantum cascade detectors in the mid-infrared

We present two InP-based quantum cascade detectors (QCDs) in the mid-infrared wavelength range. Their narrow band detection spectra are centered at 5.3 and 9μm. A vertical intersubband transition followed by a carefully designed extraction cascade, which is adapted to the LO-phonon energy, leads to 10K responsivities R of 3.2 and 9.0mA∕W and background limited detectivities DBLIP* of 2×108 and 3×109 Jones, for the 5.3 and the 9μm devices, respectively. Detection has been observed up to device temperatures of 300K (RT), albeit reasonable performance is restricted to temperatures below 150K (5.3μm) and 70K (9μm). Designed for zero bias operation, QCDs do not produce any dark current and therefore do not suffer from dark current noise and capacitance saturation at long integration times, making them ideal devices for large focal plane arrays.

Quantum cascade detectors

A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented which we called a Quantum Cascade Detector (QCD). The highest photoresponse of intersubband transition based photovoltaic detectors is demonstrated: 44 mA/W at zero applied bias. Further improvements permit to suppress the leakage current and to increase the resistivity R 0 A. Useless cross-transitions have been eliminated finally leading to a high resistance narrow band photodetector with a Johnson noise limited detectivity at 50 K comparable to QWIPs. Because they work with no dark current, QCDs are very promising for small pixel and large focal plane array applications.

Interband cascade detectors with room temperature photovoltaic operation

We investigated mid-infrared interband cascade laser structures as photodetectors, which are sensitive to normal incidence and operate in photovoltaic mode at room temperature. The proposed operation principle of these interband cascade detectors is based on the unique combination of interband photoexcitation and the much faster intersubband relaxation as well as interband tunneling recombination, which allows for the efficient collection of the photoexcited carriers. Peak responsivity and detectivity of 21 mA/W and 7.1×108cmHz1∕2∕W at λ=4.0μm are obtained for a device with cutoff wavelength of 4.4μm. Peak responsivity and detectivity of 46 mA/W and 1.4×109cmHz1∕2∕W at λ=3.0μm are obtained for another device with cutoff wavelength of 3.3μm. These detectors exhibit low noise (4.8×10−13A∕Hz1∕2) and a large product of the differential resistance and active area (19Ωcm2) at room temperature.

Quantum cascade photodetector

A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented: A quantum cascade detector (QCD). The highest photoresponse of intersubband transition-based photovoltaic detectors is demonstrated: 35mA∕W at null bias. The deduced absorption is of the same order of magnitude as that of a classical quantum-well infrared photodetector, i.e., 20%. Because they work with no dark current, QCDs are very promising for small-pixel large focal plane array applications.

High precision measurements of atmospheric nitrous oxide and methane using thermoelectrically cooled mid-infrared quantum cascade lasers and detectors

A compact, fast response, mid-infrared absorption spectrometer using thermoelectrically (TE) cooled pulsed quantum cascade (QC) lasers and TE detectors has been developed to demonstrate the applicability of QC lasers for high precision measurements of nitrous oxide and methane in the earth’s atmosphere. Reduced pressure extractive sampling with a 56 m path length, 0.5 l volume, multiple pass absorption cell allows a time response of <0.1 s which is suitable for eddy correlation flux measurements for these gases. Precision of 0.3 ppb (rms, 1 s averaging time) or 0.1% of the ambient concentration for N 2O (4 ppb or 0.2% of ambient for CH 4), has been demonstrated using QC lasers at 4.5 μm (7.9 μm for CH 4), corresponding to an absorbance precision of 4×10 −5 Hz −1/2 (8×10 −5 Hz −1/2 for CH 4). Stabilization of the temperature of the optical bench and the pulse electronics results in a minimum Allan variance corresponding to 0.06 ppb for N 2O with an averaging time of 100 s (0.7 ppb with an averaging time of 200 s for CH 4). The instrument is capable of long-term, unattended, continuous operation without cryogenic cooling of either laser or detector.

Building a cascade detector and its applications in automatic target detection

A hierarchical classifier (cascade) is proposed for target detection. In building an optimal cascade we considered three heuristics: (1) use of a frontier-following approximation, (2) controlling error rates, and (3) weighting. Simulations of synthetic data with various underlying distributions were carried out. We found that a weighting heuristic is optimal in terms of both computational complexity and error rates. We initiate a systematic comparison of several potential heuristics that can be utilized in building a hierarchical model. A range of discussions regarding the implications and the promises of cascade architecture as well as of techniques that can be integrated into this framework is provided. The optimum heuristic--weighting algorithms--was applied to an IR data set. It was found that these algorithms outperform some state-of-the-art approaches that utilize the same type of simple classifier.

Gamma cascade detectors for the space station era

Emulsion chambers provide a unique opportunity to observe gamma ray sources in the 0.1–10 TeV energy range. A new hybrid detector system is proposed, employing a scintillator ribbon fiber counter system to provide particle arrival time and direction information as well as an energy estimate, supplementing the accurate particle identification and energy determination capabilities of the emulsion chamber. The counter system is intended to be self-contained and undemanding, and will work efficiently in remote-site balloon flight exposures as well as in the Space Station environment.

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation — Part IV: The Application of the Intranuclear Cascade Model to Reactions of Pions, Nucleons, Kaons, and Their Antiparticles with Nuclei Below 6 GeV/c

An extension of the intranuclear cascade model is described. The primary hadrons may be pions, kaons, nucleons, and their antiparticles. Secondary particles produced include hyperons or anti-hypero...

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part I: Inelastic Hadron/Nucleon Collisions at Energies Below 5 GeV

A model for sampling inelastic hadron/nucleon interactions at energies below 5 GeV is described. The model describes the total hadronic cross section as a sum of quasi-two-body reaction channels. Inelastic events are sampled by first selecting one of these reaction channels and the subsequent decay of all resonances produced. Comparison with exclusive and inclusive data indicates very good agreement. The model is very well suited for hadron cascade calculations, detector simulation, and as input for models of hadron/nucleus interactions.

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part II: Inelastic Hadron/Nucleus Collisions at Energies Below 5 GeV

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part II: Inelastic Hadron/Nucleus Collisions at Energies Below 5 GeV

Performance of a Thallium Chloride Scintiliator as a Total Absorption Shower Cascade Detector

Studies have been made of the performance of a large sample of the new heavy scintillator TlCl(Be,I) as a total absorption shower cascade (TASC) detector for high energy electrons and gamma rays. The observed energy resolution for electrons in the range 0.1 to 15 GeV is reported and compared to a Monte Carlo calculation of expected fluctuations in energy leakage from the crystal volume. The performance of this new scintillator and its potential applications are discussed.

A comparison of three total absorption gamma spectrometers

Three total absorption shower cascade detectors, consisting of blocks of cadmium fluoride, lead fluoride and lead glass of similar dimensions viewed by photomultipliers, have been investigated up to 3.5 GeV on the test beam at Daresbury Nuclear Physics Laboratory. At 1 GeV the energy resolution of the cadmium fluoride detector was found to be 19% (fwhm) compared with 34% for the other two. This superior resolution arises from the fact that the response of cadmium fluoride is mainly due to scintillation compared with the pure Cherenkov response of the other two detectors. However, above 1 GeV the Cherenkov detectors exhibit a more linear variation of pulse height with energy.

A New Instrument Concept for Gamma Ray Astronomy

A new instrument concept that utilizes the principle of the Total Absorption Shower Cascade (TASC) detector is proposed for gamma ray astronomy in space. Using the TASC detector to measure the gamma ray energy and wire chamber arrays to measure the incident angle, an instrument package designed to measure gamma rays having energies greater than 100 MeV is being proposed for a large satellite such as NASA's proposed High Energy Astronomy Observatory. The proposed instrument has a minimal flux sensitivity of 2 × 10-10 photons/cm2 sr sec which will allow gamma rays with energies up to 104 GeV to be measured. An energy resolution (FWHM) for the TASC detector of ~l percent at 10 GeV has been measured and an angular resolution of ~1 degree appears to be obtainable for the wire chamber arrays.

Total absorption nuclear cascade detectors for high energy physics

A new type of detector (TANC counter) of high energy particles is proposed which operates on the principle of total absorption of all nuclear cascade products of the impinging particle. This detector will be sensitive to neutral particles (including gamma rays) as well as charged particles and will have 100% efficiency for detection. The counter can have high speed, good energy resolution, discrimination properties, large dynamic range and virtually no limit to the highest energy detectable. Some preliminary experimental results are shown which indicate that the counter will operate as expected.