Quantum dot microdrop laser

We report single-mode and multimode lasing from isolated spherical liquid microcavities containing CdSe/ZnS nanocrystal quantum dots. Lasing is observed at densities more than 2 orders of magnitude lower than previously demonstrated or theoretically predicted, assuming a uniform nanocrystal quantum dot distribution. Charged droplets, between 10 and 40 microm in size, are electrodynamically levitated and optically pumped. Substantial laser signals at low thresholds are measured from the directional emission normal to the pump beam, owing to the high Q cavity modes.     

Quantum noise of laser diodes

Abstract

Single-mode laser theory for semiconductor lasers predicts sub-Poissonian light generation for a laser quietly driven far above threshold. Experiments have shown however that only few laser diodes exhibits such reduced intensity noise. We present a review of different mechanisms that have been proposed to explain the excess noise observed in semiconductor lasers, including imperfect anticorrelations in multimode lasers, and Petermann excess noise factor in single-mode lasers.     

CauStereo: range from light in nature

Underwater, natural illumination typically varies strongly temporally and spatially. The reason is that waves on the water surface refract light into the water in a spatiotemporally varying manner. The resulting underwater illumination field forms a caustic network and is known as flicker. This work shows that caustics can be useful for stereoscopic vision, naturally leading to range mapping of the scene. Range triangulation by stereoscopic vision requires the determination of correspondence between image points in different viewpoints, which is often a difficult problem. We show that the spatiotemporal caustic pattern very effectively establishes stereo correspondences. Thus, we term the use of this effect as CauStereo. The temporal radiance variations due to flicker are unique to each object point, thus disambiguating the correspondence, with very simple calculations. Theoretical limitations of the method are analyzed using ray-tracing simulations. The method is demonstrated by underwater in situ experiments.     

Directional light scanning laser ophthalmoscope

The cone photoreceptor mosaic of the living human eye has in a limited number of cases been imaged without the use of wavefront-correction techniques. To accomplish this, the directionality of the photoreceptors, as manifested by their waveguiding properties, may be used to advantage. In the present paper we provide a model of our recently proposed directional light scanning laser ophthalmoscope [Opt. Lett. 29, 968 (2004)] together with a detailed numerical analysis of the device. The outcome is compared with experimental results.     

Bright diode laser light source

A simplified multiwavelength prototype of an axially symmetric diode laser device based on stacks made of single emitters has been made, and the performance of the device has been demonstrated experimentally. The results verify that kilowatt-level light power can be focused into a circular spot with a 1/e2 diameter of 360 microm, a focal length of 100 mm, and a numerical aperture of 0.24, thus producing an average power density in excess of 10 kW/mm2 and a brightness of 6x10(10) W m-2 sr-1. The experiments also predict that it will be possible to increase these values to more than 60 kW/mm2 and 3x10(11) W m-2 sr-1.     

Deep nulling of visible laser light

Nulling interferometry, a proposed technique for dimming a star relative to its surroundings by destructively interfering the light collected by two individual telescopes [Bracewell, Nature 274, 780-781 (1978); Shao and Colavita, Ann. Rev. Astron. Astrophys. 30, 457-498 (1992)], has the potential to permit the direct detection of nearby extrasolar planets. However, because of the extremely high degree of symmetry required for useful levels of starlight nulling, the technique remains in its infancy. We present results of laboratory experiments with a rotational shearing interferometer that are aimed at demonstrating the feasibility of deep nulling at the levels needed for direct planet detection. Our first results include the successful nulling of red laser light to a part in 10(5) and the stabilization of the null leakage to a part in 10(4).     

Quantum phase measurements and non-classical polarization states of light

Abstract

In our paper we consider the non-classical behaviour of both the Hermitian (observable) Stokes parameters of light and the phase difference of two modes that describe the quantum polarization states of optical field. To characterize the degree of polarization of light we introduce a new quantity taking into account the quantum properties of different quantum states of two orthogonally polarized modes. The problem of determination of the phase difference in two modes of optical field for the quantum polarization states of light is discussed. To describe in general such a quantum field we introduce two pairs of the phase operators: the phase angles for the Stokes parameters of light in a three-dimensional picture of the Poincaré sphere. We also consider a special type of the eight-port polarization interferometer (polarimeter) for simultaneous homodyne detection of both the Stokes parameters of light and the polarization phase operators and their fluctuations as well. Using an anisotropic (spatioperiodic) Kerr-like nonlinear medium associated with the polarization interferometer we could generate and also observe the polarization-squeezed phase states of light. The fluctuations in the phase difference between two orthogonally polarized modes for these non-classical states are less than the fluctuations for light in coherent state.     

Solid-state laser pumping by light guides

What we believe to be novel pumping schemes for lamp-pumped solid-state lasers are proposed. Based on the refractive and total internal reflection principles, curved fused-silica light guides of rectangular cross sections are used to couple the pump radiation from an arc lamp into a laser crystal. The performances of light-guide pumping schemes are analyzed through a nonsequential ray-trace program and are compared to that of a single elliptical cavity. Improved pump radiation distribution around the laser crystal was registered. The light-guide cavities also permit tailoring the pump flux distribution within the active medium. A lamp-pumped Nd:YAG laser by a light-guide cavity was built and tested. An overall laser efficiency of 1.1% was measured.     

Multiple light scattering in laser particle sizing

Multiple light scattering is an important issue in modern laser diffraction spectrometry. Most laser particle sizers do not account for multiple light scattering in a disperse medium under investigation. This causes an underestimation of the particle sizes in the case of high concentrations of scatterers. The retrieval accuracy is improved if the measured data are processed with multiple-scattering algorithms that treat multiple light scattering in a disperse medium. We evaluate the influence of multiple light scattering on light transmitted by scattering layers. The relationships among different theories to account for multiple light scattering in laser particle sizing are considered.     

Elastic laser light scattering by GaAs surfaces

Angle-resolved scattering (ARS) intensities were measured in the backscattering hemisphere for the (1 0 0) and (1 1 1) faces of GaAs single crystals. Three epitaxial layers were deposited onto the GaAs (1 0 0) single-crystalline wafers. The laser elastic light scattering shows the presence of a regular surface microrelief whose orientation corresponds to the crystallographic axes in the surface plane. We studied the statistical properties of this microrelief and determined the parameters that characterize the surface. We propose to use the ARS ratio for two wavelengths (in our case, 632.8 and 441.6 nm) to determine the topographical properties of scattering and to study crystal surface defects.     

Quantum theory of light in nonlinear media with dispersion and absorption

Abstract

We present a canonical quantum theory of radiation in nonlinear media taking into account the effects of linear dispersion and absorption in a consistent way. We start from a microscopic model and apply recently developed concepts of the quantization of radiation in dispersive and absorbing linear media and extend the theory in order to include nonlinear optical processes. We derive propagation equations in space and time for the quantized radiation field, with special emphasis on the propagation of quantum-light pulses in Kerr media. In particular, the method enables us to derive systematically the noise sources that arise naturally in the nonlinear terms.     

Erosion laser torch in the light of the gating radiation from an auxiliary laser

A gating laser illumination pulse has been used to visualize different stages of the formation of the liquid-drop phase formed by the hydrodynamic mechanism in the erosion laser torch of a metal. Analysis of the sequence of photographs obtained under different irradiation conditions has been performed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 211–215, March–April, 2008.     

Quantum light signatures and nanosecond spectral diffusion from cavity-embedded carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are considered for novel optoelectronic and quantum photonic devices, such as single photon sources, but methods must be developed to enhance the light extraction and spectral purity, while simultaneously preventing multiphoton emission as well as spectral diffusion and blinking in dielectric environments of a cavity. Here we demonstrate that utilization of nonpolar polystyrene as a cavity dielectric completely removes spectral diffusion and blinking in individual SWCNTs on the millisecond to multisecond time scale, despite the presence of surfactants. With these cavity-embedded SWCNT samples, providing a 50-fold enhanced exciton emission into the far field, we have been able to carry out photophysical studies for the first time with nanosecond timing resolution. We uncovered that fast spectral diffusion processes (1-3 ns) remain that make significant contributions to the spectral purity, thereby limiting the use of SWCNTs in quantum optical applications requiring indistinguishable photons. Measured quantum light signatures reveal pronounced photon antibunching (g(2)(0) = 0.15) accompanied by side-peak bunching signatures indicative of residual blinking on the submicrosecond time scale. The demonstrated enhanced single photon emission from cavity-embedded SWCNTs is promising for applications in quantum key distribution, while the demonstrated passivation effect of polystyrene with respect to the stability of the optical emission opens a novel pathway toward optoelectronic devices with enhanced performance.     

Fringe visibility of multimode laser light scattered through turbid water

Several years ago Swanson [Proc. SPIE 1750, 397 (1992)] performed a simple Michelson interferometric determination of the coherence length of a multimode argon-ion laser after the light passed through a tank of water. As colloidal particles were added to the water the observed coherence length (as measured by twice the distance the mirror moved for fringes to disappear) decreased. Subsequently, a series of careful experiments were performed with a single-mode laser to more accurately measure this change. In these experiments it was found that the 1.5-MHz width of the 514.5-nm line of a single-mode argon-ion laser broadened by as much as 1.3 +/- 0.2 MHz when small colloidal particles were added. At first glance such a broadening should not have resulted in any discernible change in the original Michelson experiment because the gain curve for the multimode laser is of the order of a few gigahertz. The zeros in the fringe visibility function depend on the spectral characteristics of the modes. Upon scattering, the spectral characteristics of the individual laser modes change from Voigt functions, containing both Lorentzian and Gaussian components, to primarily Gaussian. It is this change in the statistical properties of the modes, not the broadening, that accounts for the change in the fringe visibility for a multimode source.     

Scattering of light by laser fusion targets with small defects

The extended boundary condition method was used to determine the effect imperfections in small glass and metal shells have on scattered light at 10.6 microm. The results indicate that imperfections cause a shift in the locations of the minima in the differential scattering curve, a change in the extinction efficiency, and the presence of depolarized components for off-axis orientation of the object. Among these, the presence of and changes in the depolarized component are most sensitive to imperfections. We compute the depolarized scatter from shells with types I, II, and III defects and discuss the potential of light scattering as a characterization tool for laser fusion targets     

Beam homogenizer for hollow-fiber delivery system of excimer laser light

A beam homogenizer for a hollow-fiber-based, UV laser delivery system is proposed. A rectangular glass waveguide with an inner aluminum coating that has a 1-mm square cross section is attached at the output end of the circular-core hollow fiber with a 1-mm inner diameter. The rectangular waveguide generates a number of higher-order modes and results in a uniform top-hat profile. The configuration of the waveguide is designed by a ray-tracing technique so that both the low transmission loss and the high uniformity in the output beam are obtained. The fabricated waveguide shows a low loss of 0.4 dB, and the intensity variation coefficient is 7%. The output beam from the rectangular waveguide is expanded by a lens to the size larger than 10-mm square. It is also shown that the profile does not change with the bending condition.