High-efficiency Photon Research Articles

Photon storage inΛ-type optically dense atomic media. IV. Optimal control using gradient ascent

We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in $\ensuremath{\Lambda}$-type media to previously inaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical control pulses used to mediate photon storage, we open up the possibility of high efficiency photon storage in the nonadiabatic limit, in which analytical solutions to the equations of motion do not exist. This control shaping technique enables an order-of-magnitude increase in the bandwidth of the memory. We also demonstrate that the often discussed connection between time reversal and optimality in photon storage follows naturally from gradient ascent. Finally, we discuss the optimization of controlled reversible inhomogeneous broadening.

The avalanche drift diode—A back illumination drift silicon photomultiplier

Development of high quantum efficiency photon detectors is needed for many low light level (LLL) applications. Recently a new type of photodetector was introduced, the so-called Silicon PhotoMultiplier (SiPM). Its good characteristics (fast response, high gain and single photon resolution capability) make SiPM suitable for many applications. Yet its quantum efficiency is still not satisfactory ( < 40 % ) for LLL applications. A new detector concept is presented that promises very high ( > 80 % ) quantum efficiency in a wide wavelength range (300–1000 nm). Combining the drift diode with an avalanche structure placed on the opposite side of the large-area radiation entrance window on the fully depleted bulk, one obtains a large-area device that focuses the photoelectron onto a small “point-like” avalanche region. Engineering of the shallow radiation entrance window provides high quantum efficiency in the desired wavelength range. Such a device can be used as a building block for a “silicon photomultiplier”. Extensive simulations have demonstrated the validity of this concept. A production of test devices for the optimization and characterization of avalanche regions and technology parameters has been carried out. The first results from this “proof of principle” production are presented.

Self-assembled ultrafine hierarchical ZnS treelike nanoarchitectures

Ultrafine hierarchical tree-shaped nanoarchitectures of ZnS were synthesized by a H 2-assisted thermal evaporation and condensation technique. Morphology and composition of the ZnS deposit were studied by means of field emission scanning electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The deposit was found to consist of a layer of oriented submicrorods partly covered by microsheets and randomly oriented submicrowires, and three-dimensional treelike nanoarchitectures grew epitaxially on various submicrorods, microsheets, and submicrowires. The growth of the nanostructures is a spontaneous and self-assembled process. Vapor–solid (VS) growth mechanism is proposed for the formation of the treelike nanostructures because catalyst was not introduced during the synthesis process. This novel hierarchical ZnS nanoarchitecture may offer great potential for applications, including three-dimensional nanoelectronics and high efficient spatial resolved photon detector.

A novel high-efficiency single-mode single photon source

We present a novel single-mode single photon source exploiting the emission of a semiconductor quantum dot (QD) located inside a photonic wire. We first show theoretically that for optimized designs, more than 95% of the QD spontaneous emission (SE) can be injected into the fundamental guided mode of the photonic wire. A single photon collection efficiency of 17% is measured in a preliminary experiment performed on a single InAs QD located within a 250 nm diameter cylinder of GaAs. Because this photon collection strategy does not exploit the Purcell effect, it could also be efficiently applied to broadband single photon emitters such as F-centers in diamond.

Single-Crystalline Branched Zinc Phosphide Nanostructures: Synthesis, Properties, and Optoelectronic Devices

Hierarchical tree-shaped nanostructures, nanobelts, and nanowires of Zn3P2 were synthesized in a thermal assisted laser ablation process. All nanostructures are tetragonal phased Zn3P2 with excellent crystallinity and are free from an oxidization layer according to electron microscopy and X-ray diffraction analyses. Optical measurement revealed a strong absorption from the ultraviolet to near-infrared regions. Optoelectronic devices fabricated using individual nanowires demonstrate a high sensitivity and rapid response to impinging light. A crossed heterojunction of an n-type ZnO nanowire and a p-type Zn3P2 nanowire has been characterized, and it offers a great potential for a high efficient spatial resolved photon detector.

A detector for radionuclide bronchial scanning

This paper aims to describe a sub-miniature scintillation detector suitable for functional bronchial scanning and solitary pulmonary nodules detection. The device is made by a probe having diameter adequate for insertion in a catheter and external electronics for signal's analysis. The final scanner will be composed of a train of individual detectors, each one made by a scintillation crystal and a Si-avalanche photodiode operating in single-photon modality. The setup shows high-efficiency photon detection and high quantum-efficiency readout giving adequate energy resolution for efficient rejection of scattered events. The crystal can be adequately shielded to reduce the background from healthy tissues. Assuming the use of a radiopharmaceutical labeled with 99mTc, Monte Carlo simulations concerning a simple pulmonary model have been performed at 57Co lines and compared to experimental results. Furthermore, useful simulated data have been obtained at 140 keV concerning the strategy for background reduction to improve nodule localization.

Optical implementation of quantum computers

Optical quantum computation was limited to a few photon applications such as quantum cryptography and partial teleportation until 2001. Then the possibility of performing arbitrary logic conditional on certain detection outcomes was introduced by Knill, Laflamme and Milburn (Nature 2001 409 46). Simple circuits consisting of single photon sources, entangled pair sources, linear optical elements and high efficiency photon counting detectors can be used to develop probabilistic two-photon logic gates. Initially such gates show a low probability of success but can approach the success rate of deterministic (non-linear) logic at the cost of added complexity. These developments have led to the emergence of a novel field of research aimed at improving the efficiency of linear logic and developing the efficient sources and detectors for its implementation. This topical issue of Journal of Optics B: Quantum and Semiclassical Optics is devoted to recent advances in this field.

Photonic Technologies for Quantum Information Processing

The last several years have seen tremendous progress toward practical optical quantum information processing, including the development of single- and entangled-photon sources and high-efficiency photon counting detectors, covering a range of wavelengths. We review some of the recent progress in the development of these photonic technologies.

Direct observation of nonclassical photon statistics in parametric down-conversion.

We employ a high quantum efficiency photon number counter to determine the photon number distribution of the output field from a parametric down-converter. The raw photocount data directly demonstrates that the source is nonclassical by 40 standard deviations, and correcting for the quantum efficiency yields a direct observation of oscillations in the photon number distribution.

Multichannel detector–collimator for powder diffraction measurements at energy scanning x-ray absorption spectroscopy synchrotron radiation beamlines for high-pressure and high-temperature applications

We describe a modular detector system suitable to intercept the diffracted x-ray radiation (Debye–Scherrer rings) in a transmission geometry setup at monochromatic tunable synchrotron radiation beamlines. The detector consists of several independent channels composed of a motorized front slit and a rear detector slit system which can be mounted in either a vertical or a horizontal configuration. The detectors are placed at fixed scattering angles 2θ and the diffraction scan is performed by tuning the monochromator energy. The availability of a multidetector system allows one to cover a wide range of scattering vectors with limited range energy scans. The photon sensitive elements are based on CdZnTe solid state detectors which are used at ambient temperature for high efficiency photon counting in the 10–60 keV range. In alternative, conventional NaI(Tl) scintillation detectors can be integrated in the setup. The system can be mounted in a high-resolution configuration and typical widths in the range ΔE/E≃10−3 have been obtained for Bragg peaks. In these conditions the sensitivity to changes in the lattice spacing is better than 10−4. This detector system fully complements the experimental devices usually available at x-ray absorption spectroscopy beamlines and the short range structural information obtained using the x-ray absorption fine structure technique. Typical applications include high-pressure and high-temperature investigations of condensed matter.

High efficiency photon counting using stored light.

We propose a method that can, in principle, achieve nearly ideal photon counting, by combining the techniques of photonic quantum memory and ion-trap quantum-state measurements. After mapping the quantum state of a propagating light pulse onto metastable collective excitations of a trapped cold atomic gas, it is possible to monitor the resonance fluorescence induced by an additional laser field that couples only to the metastable excited state. Even with a photon collection/detection efficiency as low as 10%, it is possible to achieve photon counting with efficiency exceeding 99%.

Real-Time Detection of Single Molecules in Solution by Confocal Fluorescence Microscopy

We report real-time detection of single fluorescent molecules in solution with a simple technique that combines confocal microscopy, diffraction-limited laser excitation, and a high-efficiency photon detector. The probe volume, ∼5.0 x 10 -6 L, is defined latitudinally by optical diffraction and longitudinally by spherical aberration. With an unlimited excitation throughput and a low background level, this technique allows fluorescence detection of single rhodamine molecules with a signal-to-noise ratio of ∼10 in 1 ms, which approaches the theoretical limit set by fluorescence saturation. Real-time measurements at a speed of 500 000 data points/s yield single-molecule fluorescence records that not only show the actual transit time of a particular molecule across the probe volume but also contain characteristically long (∼50 μs) and short (∼4 μs) dark gaps. Random-walk simulations of single fluorescent molecules provide evidence that these long and short dark periods are caused mainly by boundary re-crossing motions of a single molecule at the probe volume periphery and by intersystem crossing into and out of the dark triplet state. We have also extended the use of confocal fluorescence microscopy to study individual, fluorescently tagged biomolecules, including deoxynucleotides, single-stranded primers, and double-stranded DNA. The achieved sensitivity permits dynamic structural studies of individual λ-phage DNA molecules labeled with intercalating fluorescent dyes ; the results reveal large-amplitude DNA structural fluctuations that occur on the millisecond time scale.

A high-efficiency photon detector for parallel acquisition of UV inverse photoemission spectroscopy

We describe an ultraviolet photon detector realized for parallel acquisition of eight inverse photoemission spectra in the isochromatic mode, at photon energies from 10 to 25 eV. This simple and reliable device is obtained by combining an array of eight channeltrons corresponding to the various photon energies of the spectral and a single Csl-coated photocathode.

High-sensitivity bandpass UV photon detector for inverse photoemission

The authors describe a new type of high-efficiency UV photon detector which is simple and reliable, obtained by combining the high- and low-pass filtering of a KBr coated photocathode and a CaF2 window. This device is suitable for isochromatic inverse photoemission spectroscopy.

High Efficiency Photon Counting Detectors for the FAUST Spacelab Far Ultraviolet Astronomy Payload

We compare the performance of sealed tube microchannel-plate position sensitive detectors having transmission CsI photocathodes or opaque CsI photocathodes. These devices were developed for the FAUST Spacelab payload to accomplish imaging surveys in the band between 1300Å and 1800Å. We demonstrate that photocathode quantum efficiencies in excess of 40% at 1216Å have been achieved with the transmission and the opaque CsI photocathodes. The effect of the photoelectron trajectory on the spatial resolution is assessed. Spatial resolution of <70μm FWHM has been obtained and is maintained up to event rates of 5×104 sec-1. Background rates of 0.55 events cm-2 sec-1 have been achieved and low distortion (<1%) imaging has been demonstrated.