Classical Light Sources Research Articles

用于经典和非经典光源的量子点研究进展

Recent advances in quantum dots (QDs) for classical and non-classical light sources are presented. We have established metal organic chemical vapor deposition (MOCVD) technology for InAs-based Q D lasers at 1.3 \mm and achieved ultralow threshold in Q D lasers with photonic crystal (PhC) nanocavity. In addition, single photon emitters at 1.55 µm, GaN-based single photon sources operating at 200 K, and high- PhC nanocavity have been demonstrated.

Classical correlated imaging from the perspective of coherent-mode representation

We use coherent-mode representation of partially coherent fields to analyze correlated imaging with classical light sources. This formalism is very useful to study the imaging quality. By decomposing the unknown object as the superposition of different coherent modes, the components corresponding to small eigenvalues cannot be well imaged. The generated images depend crucially on the distribution of the eigenvalues of the coherent-mode representation of the source and the decomposition coefficients of the objects. Three kinds of correlated imaging schemes are analyzed numerically.

Gradually tapered light pipes for illumination of LED projectors

Abstract— LEDs are totally different from classical light sources: they have a different shape, radiation pattern, driving requirements, etc. Therefore, the illumination engine, which determines the brightness and uniformity of the system, has to be redesigned for LED‐based projectors. A compact illumination system based on gradually tapered light pipes (GTLP) will be presented. The GTLP collects, reshapes, and uniformizes the light flux from the LED to illuminate the light‐valve uniformly. The design and the simulations have been completed. The result is a uniformly illuminated rectangular beam at the end of the pipe with an efficiency of 81.1%. Afterwards, the light pipe was fabricated, and the experimentally measured efficiency is 76.9%, which demonstrates a successful manufacturing process. Finally, two recycling techniques to enhance the brightness have been applied and these enhancements were experimentally observed.

Generation and manipulation of nonclassical light using photonic crystals

Photonic crystal cavities can localize light into nanoscale volumes with high quality factors. This permits a strong interaction between light and matter, which is important for the construction of classical light sources with improved properties (e.g., low threshold lasers) and of nonclassical light sources (such as single and entangled photon sources) that are crucial pieces of hardware of quantum information processing systems. This article will review some of our recent experimental and theoretical results on the interaction between single quantum dots and photonic crystal cavity fields, and on the integration of multiple photonic crystal devices into functional circuits for quantum information processing.

High resolution molecular physics studies using a laser-based tunable XUV source at 10 7 resolving power

At the Laser Centre Vrije Universiteit, a tunable and narrowband laser-based source of extreme ultraviolet (XUV) radiation was developed using non-resonant third harmonic generation (THG) of powerful laser pulses in the ultraviolet range. The laser source is either a commercial or modified pulsed dye laser (grating-based) or a pulsed-dye-amplifier, which is injection seeded by the output of a continuous wave ring-dye laser or a Ti:sapphire laser. This system opens the possibility to perform spectroscopic research at wavelengths 70–110 nm at a resolution unattainable with classical light sources. Particularly in the range 90–110 nm a source bandwidth of 0.01 cm −1 can be employed. Examples of gas-phase molecular beam spectroscopic studies on diatomic molecules, such as H 2, N 2 and CO will be presented. Another feature of Q-switch based XUV laser sources is the possibility to perform multi-step multi-photon experiments in molecules, uncovering otherwise inaccessible states.

Number Statistics of Molecules Formed from Ultracold Atoms

We calculate the number statistics of a single-mode molecular field excited by photo-association or via a Feshbach resonance from an atomic Bose-Einstein condensate (BEC), a normal atomic Fermi gas, and a Fermi system with pair correlations (BCS state). We find that the molecule formation from a BEC leads for short times to a coherent molecular state in the quantum optical sense. Atoms in a normal Fermi gas, on the other hand, result for short times in a molecular field analog of a classical chaotic light source. The BCS situation is intermediate between the two and goes from producing an incoherent to a coherent molecular field with an increasing gap parameter. This distinct signature of the initial atomic state in the resulting molecular field makes single molecule counting into a powerful diagnostic tool.

Geometrical optics in correlated imaging systems

We discuss the geometrical optics of correlated imaging for two kinds of spatial correlations corresponding, respectively, to a classical thermal light source and a quantum two-photon entangled source. Due to the different features in the second-order spatial correlation, the two sources obey different imaging equations. The quantum entangled source behaves as a mirror, whereas the classical thermal source looks like a phase-conjugate mirror in the correlated imaging.

Spectroscopy by frequency-entangled photon pairs

Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.

Photon distribution function, tomograms and entanglement in stimulated Raman scattering

Several aspects of the stimulated Raman scattering process are studied using the model of a two-dimensional oscillator. The photons of the Stokes mode are taken as one mode of the oscillator and the phonons of the medium are taken as the other mode of the oscillator. The interaction Hamiltonian of the photons and phonons is taken to be quadratic in the annihilation and creation operators of photons and phonons. The laser is considered as a classical light source and its depletion is neglected. The photon?phonon joint probability distribution function is found and expressed in terms of Hermite polynomials of four variables. The general formula for the photon number probability distribution as a function of the laser-field intensity and the medium parameters is obtained in terms of Hermite polynomials of two variables. It is shown that the phenomenon of entanglement appears in photon?phonon modes due to the interaction of the light with the medium. The tomograms of the photon?phonon states and (averaged over the phonon mode) photon states are investigated within the framework of a symplectic tomography scheme.

Resolution and apodization in images generated by twin photons

We show that an image of an object is obtained when at least one of the photons of a parametric down-converted pair illuminates the object and the two photons are detected in coincidence after they have been transmitted by two lenses. The image is mathematically described by a quantum fourth-order correlation function that differs from the classical image description in two aspects. The quantum image is produced by a nonlocal effective lens whose aperture is described by a compressed convolution of the magnitude of lens transmission functions. The image is generated by the entangled state two-photon light source in which the effective wavelength is equal to the de Broglie wavelength $\ensuremath{\lambda}/2,$ where $\ensuremath{\lambda}$ is the wavelength associated to the individual photons. Images can be obtained with a resolution better than the obtained with coherent classical light sources. Better resolution and strong apodization effects are observed.

Technical approaches for high-average-power free-electron lasers

Free-electron-laser (FEL) oscillators have only recently achieved their original promise as producers of high-power, short-wavelength, tunable radiation. Room-temperature accelerator systems have generally had limited duty factor due to excessive Ohmic losses on cavity walls. The application of superconducting radio-frequency (SRF) technology has now permitted an increase by more than two orders of magnitude in FEL average power due just to increased duty factor in continuous-wave operation. A concurrent technical development that leveraged the high efficiency of SRF linacs was the demonstration of beam energy recovery while lasing. This leads to high overall efficiency and scales favorably to systems with even higher average power. This paper will discuss the issues relating to high-average-power light sources. The planned and demonstrated performance of several FEL facilities will illustrate the sizable advantages that superconducting radio frequency offers for high average flux and output multiplexing for several simultaneous users. An important new class of light sources, energy-recovering linacs, will be introduced.

The Emission of a Single Photon from a Single Atom or Molecule - An Experimenter's View

Crucial experiments of physics, such as the quantum mechanical version of the double slit experiment, have so far not been performed with true single (antibunching) photons. Instead, attenuated classical light sources such as bulbs or lasers have been suggested to provide the photons in these experiments. Since attenuators do not change photon statistics, i.e. do not convert classical into non - classical light, reliable single photon beams cannot be generated on this way. Antibunching sources, for example single molecules, are required. Due to the lack of such sources in the past, some extrapolations from the many - photon case to the one photon case have remained speculative, for example the long wavetrain model for a single photon. Alternative hypotheses, elaborated by considering details of the emission of single photons by single molecules are equally probable. Arguments are presented which disfavour the wavetrain model and favour the short pulse as a model for a photon.

Tomographic Description of Stimulated Brillouin Scattering of Light

The process of stimulated Brillouin scattering is described by the two‐dimensional oscillator model. Photons of the Stokes mode are described by one mode of the oscillator, and acoustic phonons are described by the other mode. The interaction of photons and acoustic phonons is assumed to be quadratic in the creation and annihilation operators of photons and phonons. The laser is considered as a classical light source and its depletion is neglected. New time‐dependent integrals of motion and the photon–phonon probability distribution function are found. The mean Stokes photon number and the mean acoustic phonon number are expressed as functions of the medium parameters (initial dispersions) and the interaction parameter (coupling constant). The classical propagator for stimulated Brillouin scattering and tomograms of the photon and phonon states are investigated within the framework of the symplectic‐tomography scheme.

Some comments on the two prism tunnelling experiment

We show that the two prism tunnelling experiment of Mizobuchi and Ohtake [Phys. Lett. A 168 (1992) 1] does not verify the quantum optical prediction due to insufficient statistical precision in the anticoincidence measurement. We reanalyze their data and show that the observed number of coincidences is actually even larger than what is expected from a classical coherent light source.

Optical pumping with nonclassical light.

Optical pumping between ground states of a multilevel atom with low-intensity finite-bandwidth squeezed light is shown to exhibit significant qualitative and quantitative differences in behavior in comparison with optical pumping by standard classical light sources. \textcopyright{} 1996 The American Physical Society.

Nonclassical excitation for atoms in a squeezed vacuum.

The two-photon transition ${6S}_{1/2}\ensuremath{\rightarrow}{6D}_{5/2}$ is investigated for trapped atomic cesium excited by squeezed light. The rate $R$ of two-photon excitation versus intensity $I$ is observed to be consistent with the functional form $R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\beta}}_{1}I+{\ensuremath{\beta}}_{2}{I}^{2}$, extending into a region with slope 1.3. This departure from the quadratic form for classical light sources is due to the fundamental alteration of atomic radiative processes by the nonclassical field.

Reduction of quantum fluctuation and suppression of the Gordon–Haus effect with phase-sensitive linear amplifiers

Compared with the use of phase-insensitive linear quantum amplifiers of the same gain G, the use of phase-sensitive linear amplifiers on phase coherent classical light sources in an amplifier-attenuator chain reduces the total quantum noise power by a factor of 4, the homodyne noise variance by 2, and the photon number variance by 2-8 and suppresses the Kerr effect linear phase fluctuation variance as well as the soliton timing-error variance by 2G(2).

PHOTOSENSITIZERS IN ORGANIZED MEDIA: SINGLET OXYGEN PRODUCTION AND SPECTRAL PROPERTIES

Abstract— Measurement of singlet oxygen production by porphyrin‐type photosensitizers in simple buffer solutions show that TPPS is more efficient than PII (Photofrin II) or than hematoporphyrin. This behavior was observed using three independent analytical detection methods for 1O2: RNO bleaching, tryptophan degradation, and oxygen consumption. Similar results were obtained when irradiating with a classical light source or with a pulsed dye laser. Addition of EPC liposomes to the buffer solution caused a decrease of efficiency for TPPS and an increase for PII. Addition of BSA shows the same relative pattern: a small increase of efficiency for TPPS and a tenfold increase for PII. These changes can be ascribed to specific interactions between the sensitizer molecules and the organized medium. Since changes in the fluorescence properties are also due to interactions with the medium, we monitored the emission of the sensitizers as a function of the environment. The fluorescence peak positions (at 648, 705 nm for TPPS and at 615, 677 nm for PII) were all red shifted. The intensities show an increase, particularly for PII in liposomes, due to a marked change in the microviscosity.

Mobile remote sensing system for atmospheric monitoring

A mobile optical remote sensing system for environmental monitoring is described. The system, housed in a full-size truck with a laboratory floor surface of 6.0 × 2.3 m2, is mainly intended for differential absorption lidar (DIAL) applications but can also be used for laser-induced fluorescence monitoring and for absorption measurements using classical light sources. The system has a 40-cm diam receiving telescope and a fully steerable flat mirror in a transmitting/receiving dome. A Nd:YAG-pumped dye laser with auxiliary nonlinear frequency conversion is the preferred transmitter in DIAL measurements. Measurement examples for atmospheric SO2 and NO2 monitoring with automatic concentration map drawings are given and further uses are discussed.

Realization of an electron spectrometer using a toroidal magnetic deflector

We present some aspects of the realization of a new angular resolved photoemission spectrometer using a magnetic deflector. The photoelectrons are dispersed according to their energy and emission angle and focused onto a detector where the band structure appears in real time. The prototype has been realized around a toroidal magnetic field optimized by computer simulation. We discuss here the energy and the angle resolution of the whole system, related to some compromises in the technical realization as the field limit effects. The main result is that we obtain a complete display of the valence-band structure (in a plane) with a classical light source in an integration time of 10 s, which is shorter than the time needed by a classical spectrometer by several orders of magnitude.