Quantum Efficiency Of Photodetectors Research Articles

Demonstrating multipartite entanglement of single-particleWstates: Linear optical schemes

We present two linear optical schemes using nonideal photodetectors to demonstrate inseparability of W-type N-partite entangled states containing only a single photon. First, we show that the pairwise entanglement of arbitrary two modes chosen from N optical modes can be detected using the method proposed by Nha and Kim [Phys. Rev. A 74, 012317 (2006)], thereby suggesting the full inseparability among N parties. In particular, this scheme is found to succeed for any nonzero quantum efficiency of photodetectors. Second, we consider a quantum teleportation network using linear optics without auxiliary modes. The conditional teleportation can be optimized by a suitable choice of the transmittance of the beam splitter in the Bell measurement. Specifically, we identify the conditions under which maximum fidelity larger than classical bound 2/3 is achieved only in cooperation with other parties. We also investigate the case of on-off photodetectors that cannot discriminate the number of detected photons.

Electronic states inGe∕Siquantum dots with type-II band alignment initiated by space-charge spectroscopy

Space-charge spectroscopy was employed to study electronic structure of a stack of four layers of Ge quantum dots (QD's) coherently embedded in an $n$-type Si(001) matrix. Evidence for an electron confinement in Si in the vicinity of neutral Ge dots was found. From the temperature- and frequency-dependent measurements the electron binding energy was determined to be $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Existence of localized electronic states is explained by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried Ge dots. To support experimental results we performed numerical analysis of three-dimensional strain distribution and electronic structure of the sample under investigation. The strain distribution was found in terms of atomic positions using a valence-force-field model with a Keating interatomic potential. The electronic energy levels were calculated by solving a three-dimensional effective mass Schr\"odinger equation. The carrier confinement potential in this equation is modified by the strain distribution. The calculated confined eigenenergies agree with our experimental values deduced from the admittance spectroscopy. The data obtained in this work may serve as a guideline to interpret efficient photo- and electroluminescence as well as enhanced quantum efficiency of photodetectors and solar cells with Ge QD's stacked in a multilayer structure.

Standard Photometric Systems

▪ Abstract Standard star photometry dominated the latter half of the twentieth century reaching its zenith in the 1980s. It was introduced to take advantage of the high sensitivity and large dynamic range of photomultiplier tubes compared to photographic plates. As the quantum efficiency of photodetectors improved and the wavelength range extended further to the red, standard systems were modified and refined, and deviations from the original systems proliferated. The revolutionary shift to area detectors for all optical and IR observations forced further changes to standard systems, and the precision and accuracy of much broad- and intermediate-band photometry suffered until more suitable observational techniques and standard reduction procedures were adopted. But the biggest revolution occurred with the production of all-sky photometric surveys. Hipparcos/Tycho was space based, but most, like 2MASS, were ground-based, dedicated survey telescopes. It is very likely that in the future, rather than making a measurement of an object in some standard photometric system, one will simply look up the magnitudes and colors of most objects in catalogs accessed from the Virtual Observatory. In this review the history of standard star photometry will be outlined, and the calibration and realization of standard systems will be examined. Finally, model atmosphere fluxes are now very realistic, and synthetic photometry offers the best prospects for calibrating all photometric systems. Synthetic photometry from observed spectrophotometry should also be used as a matter of course to provide colors within standard systems and to gain insights into the spectra and colors of unusual stars, star clusters and distant galaxies.

Ultraviolet radiation photodetectors based on structures consisting of a metal and a wide-bandgap semiconductor

Recently, much attention has been given to measuring and monitoring ultraviolet radiation from the Sun and artificial sources. Detectors based on various wide-bandgap surface-barrier structures, which are characterized by a linear dependence of the photocurrent on incident power density in the range of 10−2–103 W/m2 and can record various kinds of ultraviolet radiation, are described. For example, GaP detectors with a UFS-6 filter have a spectral photosensitivity range corresponding to that of solar ultraviolet radiation on the Earth’s surface. The spectral sensitivity of 4H-SiC surface-barrier photodetectors corresponds to the spectral curve of the bactericidal effect produced by ultraviolet radiation. A model has been developed for explaining the process of short-wavelength photoelectric conversion. According to this model, photogenerated electrons and holes can unite into hot excitons, being thus excluded from the photoelectric conversion process. The rise in quantum efficiency with increasing temperature, which has been established experimentally for photodetectors based on Schottky barriers, is attributed to the capture of photogenerated carriers by traps arising from fluctuations of the conduction and valence band edges, with subsequent thermal release of these carriers. These fluctuations are related to imperfections in the surface layer of the semiconductor, which is confirmed by the temperature independence of the quantum efficiency of photodetectors based on p-n structures.

Teleportation improvement by inconclusive photon subtraction

Inconclusive photon subtraction (IPS) is a conditional measurement scheme to force nonlinear evolution of a given state. In IPS the input state is mixed with the vacuum in a beam splitter and then the reflected beam is revealed by ON/OFF photodetection. When the detector clicks we have the (inconclusive) photon subtracted state. We show that IPS on both channels of an entangled twin-beam of radiation improves the fidelity of coherent state teleportation if the energy of the incoming twin-beam is below a certain threshold, which depends on the beam splitter transmissivity and the quantum efficiency of photodetectors. We show that the energy threshold diverges when the transmissivity and the efficiency approach unit and compare our results with that of previous works on {\em conclusive} photon subtraction.

Intercomparison of a correlated-photon-based method to measure detector quantum efficiency.

We report on the absolute calibration of photodetector quantum efficiency by using correlated photon sources, performed independently at two laboratories, the National Institute of Standards and Technology and the Istituto Elettrotecnico Nazionale (IEN). The goal is to use an interlaboratory comparison to demonstrate the inherent absoluteness of the photon correlation technique by showing its independence from the particular experimental setup. We find that detector nonuniformity limited this comparison rather than uncertainty inherent in the method itself. The ultimate goal of these investigations is development of a robust measurement protocol that allows the uncertainties of individual measurements to be determined experimentally and verified operationally. Furthermore, to demonstrate the generality of the procedure, the IEN measurement setup was also used to calibrate a fiber-coupled avalanche photodiode module. Uncertainties are evaluated for the detector both with and without fiber coupling and differences are discussed. The current IEN setup using a thinner and higher transmittance nonlinear crystal for the generation of correlated photons shows a significant improvement in overall accuracy with respect to previously reported results from IEN [Metrologia 32, 501-503 (1996)].

Measurement of the dynamic response of low-gain solid-state photodetector under weak pulse illumination

This paper presents the development of a Tunable Light Pulse Generator built to measure the quantum efficiency of photodetectors under continuous or pulsed (20ns FWHM) illumination as a function of wavelength in the Visible–UV region. For this purpose, a miniature Hamamatsu R5600U-04 PMT with low cathode resistivity can be used as reference detector. Dedicated electronics was developed in order to measure simultaneously the cathode and anode currents. This should allow to determine precisely the gain as a function of the high voltage applied to the PMT. Preliminary measurements using the TLPG do not demonstrate significant differences between the dynamic (∼10000 photons) and DC responses of PIN photodiodes down to 300nm.

Measurement of the quantum efficiency of photodetectors by parametric fluorescence

An experimental setup has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute calibration of photodetectors in the photon-counting regime by means of correlated photons in parametric fluorescence. A nonlinear crystal of lithium iodate is pumped by an argon-ion laser at 351.2 nm, generating a broadband source of correlated photons from the incoming wavelength to the far-infrared. Photomultipliers and solid-state, single-photon detectors are employed, operating in the photon-counting regime with very low dark counts. Quantum efficiency is measured at 633 nm. The results show the correlated photons to be a promising technique for radiometry. The advantages of this as opposed to a conventional method at low power levels are shown.

Feedback-assisted homodyne detection of phase shifts.

The problem of noise from external feedback control is addressed for homodyne detection of optical phase shifts. Two different schemes are analyzed: the conventional single-homodyne detection, and a two-quadrature scheme, which involves couples of independent measurements of two conjugated quadratures. The effectiveness of the feedback mechanism in both schemes is studied versus the feedback coupling parameter and high-sensitive detection regimes are discussed. The effect of nonunit quantum efficiency of photodetectors is also considered. It is shown that nonunit quantum efficiency affects phase sensitivity in the single-quadrature scheme to a larger extent than in the double-quadrature one. \textcopyright{} 1996 The American Physical Society.

Feasible phase detection with ideal sensitivity

We present a first feasible scheme for detecting the phase of a single mode of radiation with ideal RMS sensitivity N n 1 versus the average number of photons N n .I t involves pairs of alternate independent homodyne measurements of two conjugated quadratures on a weakly squeezed state at the input. Nonunit quantum efficiency of photodetectors degrades phase sensitivity leading to a power law N n ./ , with increasing versus . In phase-sensing interferometers minute variations of environmental parameters are detected through changes in the phase shift of a light beam relative to a local oscillator (LO). The back-action effect of radiation pressure on the measured parameter poses the problem of optimizing phase sensitivity for a given average number of photons N

Biphoton fields for quantum-efficiency measurements

This paper reports on an experiment performed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN), aiming at the production of biphoton fields by parametric scattering of light in a nonlinear crystal of lithium iodate. The blue line at 457,9 nm from an argon laser is used as pumping radiation, thereby resulting in a fluorescence in the visible region with degenerate pairs of photons at about 916 nm. These biphoton fields are well suited to the measurement of the quantum efficiency of photodetectors in the photon-counting regime and to the realization of an absolute source of radiation.

Absolute meter of photodetector quantum efficiency based on the parametric down-conversion effect

The quantum phenomena of parametric down conversion have been used for absolute measurement of the photodetector quantum efficiency of ultra-low-light radiation ranging from 10-12 to 10-15 W, which is equivalent to photon fluxes of 107 to 104 s-1. The process of parametric down conversion gives rise to highly correlated (in time and space) photon flux pairs. We describe the method, experimental investigation, and a new device involving the measurement of the coincidence rate of photodetection of these two correlated beams of light. The coincidence is lowered by a nonunit quantum efficiency of either detection. This fact was used for the definition of the absolute value of both photodetector's quantum efficiencies.

Absolute Measurement of Quantum Efficiency Based on Parametric Down-conversion Effect

A new radiometric method which employs quantum properties of radiation and does not require the use of standard radiation sources and receivers has been suggested. This method uses the process of three-photon down conversion in non-central-symmetrical media to measure the quantum efficiency of photodetectors.

Absolute standardless calibration of photodetectors based on quantum two-photon fields

A new method of absolute calibration of photodetectors based on a nonclassical effect in nonlinear optics is discussed. The combined influence of a monochromatic flux of pump photons and quantum vacuum noise on a nonlinear crystal with no center of symmetry results in the appearance of rigorously correlated pairs of photons with continuous spectral distribution in the spontaneous parametric scattering of light (spontaneous parametric downconversion) process. The presence of an optical field in a broad spectral range created by the two-photon states (biphotons) makes it possible to develop a new method of measuring the spectral distribution of the absolute value of the quantum efficiency of photodetectors, both in photon counting and in analog regimes, that does not use any calibrated standard light sources (étalons). The feasibility of the method is demonstrated on different types of photomultiplier tube.

Effective quantum efficiency of photodetectors for photon energies much larger than threshold

Effective quantum efficiency of photodetectors for photon energies much larger than threshold

Detective Quantum Efficiency of Photodetectors with Some Amplification Mechanisms

A detector model is proposed for the type of detection that occurs with phosphorescent screens or photo-cathode detection; that is, detection by means of absorption and secondary-emission amplification. The detective quantum efficiency for this type of detector is obtained in the case that the primary stream as well as the production of secondary events from each primary event can be approximated by Poisson distributions.If Q is the average number of secondary events produced from each incident photon, the detective quantum efficiency QD becomes QD=Q/(1+Q).