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We review the technique named heterodyne speckle velocimetry and present two applications for testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded with small tracking particles (diameter 300 nm) and fluxed between the two parallel planes of a cell with constant or variable cross section. In the first case the velocity distribution was constant along the direction parallel to the planes and was in excellent agreement with the expected Poiseuille profile along the orthogonal direction. In the second case, where velocity gradients were present also along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid flux within an accuracy of 1%. [ABSTRACT FROM AUTHOR]

The aberration theory applied to co-axial optical systems is extended to off-axial systems, for which third-order aberration coefficients are considered. The derived aberrations are analyzed using three-dimensional ray bundles, spot diagrams, and image charts, and classified in relation to the system symmetry. This theory is very useful for optical designers, allowing them to clarify the relationship between the structures of off-axial optical systems and the corresponding off-axial aberrations. [ABSTRACT FROM AUTHOR]

Laser sources have been promised for many years to be better light sources as compared to traditional lamps or light-emitting diodes (LEDs) for projectors, which enable projectors having wide colour gamut for vivid image, super brightness and high contrast for the best picture quality, long lifetime for maintain free operation, mercury free, and low power consumption for green environment. A major technology obstacle in using lasers for projection has been the speckle noise caused by to the coherent nature of the lasers. For speckle reduction, current state of the art solutions apply moving parts with large physical space demand. Solutions beyond the state of the art need to be developed such as integrated optical components, hybrid MOEMS devices, and active phase modulators for compact speckle reduction. In this article, major methods reported in the literature for the speckle reduction in laser projectors are presented and explained. With the advancement in semiconductor lasers with largely reduced cost for the red, green and the blue primary colours, and the developed methods for their speckle reduction, it is hoped that the lasers will be widely utilized in different projector applications in the near future. [ABSTRACT FROM AUTHOR]

We propose a robust method that allows a periodic or a chaotic multi-stable system to be transformed to a monostable system at an orbit with dominant frequency of any of the coexisting attractors. Our approach implies the selection of a particular attractor by periodic external modulation with frequency close to the dominant frequency in the power spectrum of a desired orbit and simultaneous annihilation of all other coexisting states by positive feedback, both applied to one of the system parameters. The method does not require any preliminary knowledge of the system dynamics and the phase space structure. The efficiency of the method is demonstrated in both a non-autonomous multi-stable laser with coexisting periodic orbits and an autonomous Rösslerlike oscillator with coexisting chaotic attractors. The experiments with an erbium-doped fibre laser provide evidence for the robustness of the proposed method in making the system monostable at an orbit with dominant frequency of any preselected attractor. [ABSTRACT FROM AUTHOR]

With laser polishing, the roughness of ground glass surfaces can be significantly reduced. With process speeds up to 1 cm2/s independent of the processed surface shape, the resulting roughness is already sufficient for illumination optics. To further reduce the roughness, the polishing process itself will be optimized and moreover combined with a subsequent laser based form correction. Within this paper, results of laser polishing as well as laser form correction and combination of the two processes are presented and discussed. [ABSTRACT FROM AUTHOR]

We present a new sample holder compatible with ELMITEC Photoemission Electron Microscopes (PEEMs) containing an optical lens and a mirror. With the integrated optical elements, a laser beam is focused from the back side of the sample at normal incidence, yielding a minimum spot size of about 1 µm. This opens up new possibilities for local laser excitations in PEEM experiments such as imaging all-optical magnetization switching at a small length scale. [ABSTRACT FROM AUTHOR]

Laser range-gated imaging systems can obtain the images of targets hidden around a corner by using an intermediary reflective surface with certain specular reflection characteristics. This imaging mode is called non-line-of-sight imaging. The target signal irradiance and disturbance radiation on the photo-detector of a non-line-of-sight imaging system are analyzed based on the modeling of an intermediary reflective surface, and an image contrast model of a non-line-of-sight imaging system is constructed. The effects of the reflective characteristics of an intermediary reflective surface and the distance between the intermediary reflective surface and the target or the detector on the image quality are analyzed in terms of the parameters of a typical non-line-of-sight imaging system. The simulation results show that a laser range-gated imaging system is indispensable for non-line-of-sight imaging with commonly used intermediary reflective surfaces without significant specular reflection characteristics, and the distance of the intermediary reflective surface from the target has a significant effect on the non-line-of-sight imaging. When the locations of detector and target are fixed, the non-line-of-sight imaging system can hardly identify the target if the intermediary reflective surface is closer to the target. In practice, the performance of the non-line-of-sight imaging system can be maximized using an appropriate usage strategy. [ABSTRACT FROM AUTHOR]

Controlling and reversing the effects of loss are major challenges in optical systems. For lasers, losses need to be overcome by a sufficient amount of gain to reach the lasing threshold. In this work, we show how to turn losses into gain by steering the parameters of a system to the vicinity of an exceptional point (EP), which occurs when the eigenvalues and the corresponding eigenstates of a system coalesce. In our system of coupled microresonators, EPs are manifested as the loss-induced suppression and revival of lasing. Below a critical value, adding loss annihilates an existing Raman laser. Beyond this critical threshold, lasing recovers despite the increasing loss, in stark contrast to what would be expected from conventional laser theory. Our results exemplify the counterintuitive features of EPs and present an innovative method for reversing the effect of loss. [ABSTRACT FROM AUTHOR]

The action mechanism of high repetitive ultra-short laser interaction on electro-optic system has been drawn great attention recently. The experimental damage effect and mechanism of single and multiple-pulse picosecond lasers on Wat-902B interline charged coupled device (CCD) are reserched. The experimental setup mainly includes lasers, test subject, and camera. It maintains that the picosecond laser points at the optical entrance puil of camera all the time. The camera is installed on an electric revolving stage to control the time of intersection between a laser and the test subject. The second moment method is employed to obtain the laser diameters on CCD surface and its accuracy is better than 20.3%. The experimental results show that the functional damage threshold of multiple-pulse laser is about 13.6~121.0 mJ/cm², which is severely lower than that of 1.5 ns and 400 ps kilohertz-repetition-rate single-pulse lasers, approximating 263~1 146 mJ/cm². The damage mechanism of single-pulse laser is to lead to short circuit between CCD vertical transfer electrode lines, but the damage mechanism of multiple-pulse laser is obviously different from that of single pulse laser, which is to cause an accumulated damage effect. [ABSTRACT FROM AUTHOR]

Idler wave absorption is important in optical parametric oscillators (OPOs). We show through both numerical simulation and experiment that proper idler wave absorption coefficient could make OPOs perform better in conversion efficiency. If the coefficient becomes larger or smaller than the proper value, the conversion efficiency would be lower. A periodically poled lithium niobate (PPLN) OPO is set to verify the numerical results. Moreover, different pump power is used in the experiment research. It shows that the proper value is changing with the pump power. It shows that idler wave absorption should be considered comprehensively with pump wave power in efficiency OPO designing. [ABSTRACT FROM AUTHOR]

An automated data acquisition and processing system is established to measure the force applied by an optical trap to an object of unknown composition in real time. Optical traps have been in use for the past 40 years to manipulate microscopic particles, but the magnitude of applied force is often unknown and requires extensive instrument characterization. Measuring or calculating the force applied by an optical trap to nonspherical particles presents additional difficulties which are also overcome with our system. Extensive experiments and measurements using well-characterized objects were performed to verify the system performance. [ABSTRACT FROM AUTHOR]

Laser range-gated imaging systems can obtain images of targets hidden around the corner, with an intermediary reflective surface with certain specular reflection characteristics. This imaging mode is called non-line-of-sight imaging. This paper describes a simulation of the target signal illuminance and disturbance radiation on the photosensitive surface of a non-line-of-sight imaging system based on modeling of an intermediary reflective surface. Meanwhile, an image contrast model of a non-line-of-sight imaging system is constructed. Simulation of the image contrast for a laser range-gated imaging system as a non-line-of-sight imaging equipment was carried out by analyzing the effects of varying the target signal illuminance and intermediary reflective surface reflection. Our simulation results show that the reflection characteristics of the intermediary reflective surface have a significant effect on the non-line-of-sight imaging. Although ordinary active laser imaging can realize non-line-of-sight imaging for an intermediary reflective surface with significant specular reflection characteristics, a laser range-gated imaging system is indispensable for non-line-of-sight imaging with commonly used intermediary reflective surfaces without significant specular reflection characteristics. The image contrast model of non-line-of-sight imaging constructed in this paper provides insights into the theoretical analysis and system design, as well as practical application of non-line-of-sight imaging. [ABSTRACT FROM AUTHOR]

A new design of vertical external cavity surface emitting laser (VECSEL) with diamond-based high contrast gratings is proposed. The self-consistent model of laser operation has been calibrated based on experimental results and used to optimize the new proposed device and to perform comparative thermal and optical analysis of conventional and double-diamond high-contrast-grating VECSELs. The proposed design considerably reduces the dimensions and complexity of the device and provides up to 80% increase of the maximum emitted power as compared with the conventional design. [ABSTRACT FROM AUTHOR]

We present a 5-km-long Raman fiber laser that delivers pulses at high harmonics of the fundamental cavity repetition rate, up to 1 GHz. The observed nanosecond pulses that propagate in an anomalous dispersion regime possess a complex noise-like structure with a coherence time of around 1 picosecond. [ABSTRACT FROM AUTHOR]

In the time-reversed counterpart to laser emission, incident coherent optical fields are perfectly absorbed within a resonator that contains a loss medium instead of a gain medium. The incident fields and frequency must coincide with those of the corresponding laser with gain. We demonstrated this effect for two counterpropagating incident fields in a silicon cavity, showing that absorption can be enhanced by two orders of magnitude, the maximum predicted by theory for our experimental setup. In addition, we showed that absorption can be reduced substantially by varying the relative phase of the incident fields. The device, termed a "coherent perfect absorber," functions as an absorptive interferometer, with potential practical applications in integrated optics. [ABSTRACT FROM AUTHOR]

It is now possible to exercise a high degree of control over the velocity at which light pulses pass through material media. This velocity, known as the group velocity, can be made to be very different from the speed of light in a vacuum c. Specifically, the group velocity of light can be made much smaller than c, greater than c, or even negative. We present a survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that work in room-temperature solids. We also describe some applications of slow light. [ABSTRACT FROM AUTHOR]

We present experimental results demonstrating enhanced current modulation of an antireflection-coated edge-emitting laser diode placed in an external cavity. By eliminating the internal cavity of the laser diode and matching the external cavity free spectral range to the modulation frequency we have increased the modulation response up to nearly complete carrier suppression. We demonstrate the tunability of this enhanced modulation over a range of more than 3 GHz. The power of the modulated beam has been measured to be 10 mW. We have recorded a beat note between the first two optical sidebands of width 1 Hz at 6.834 GHz (corresponding to the hyperfine splitting of the 87Rb ground state). This technique enables the generation of two high-power phase-locked beams for coherent manipulation of atomic states. [ABSTRACT FROM AUTHOR]

Monitoring the optical field energies in an intracavity cascaded crystalline pulsed Raman laser enables us to probe the dynamics and optimise the performance of the laser, which produces up to 2.1 W average output power at 4 wavelengths between 532 and 636 nm selectable by simple angle tuning. [ABSTRACT FROM AUTHOR]

Acousto-optically Q-switched operation of a Ho:SSO laser is reported for the first time. An average power of 2.23 W was obtained at a pulse repetition frequency from 5 to 20 kHz, with a corresponding to optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 20%. The highest energy per pulse of 0.44 mJ in 28 ns was achieved at 2112 nm with a repetition rate of 5 kHz and peak power of 15 kW. The lifetime of Ho3+ in the Sc2SiO5 crystal host was also measured. [ABSTRACT FROM AUTHOR]

Advances in free electron lasers (FELs) which generate high energy photons are expected to open novel nonlinear optics in the x-ray and vacuum ultraviolet (VUV) regions. In this paper, we report a new method for performing VUV-FEL focusing experiments. A VUV-FEL was focused with Kirkpatrick-Baez optics on a multilayer target, which contains fused silica as a fluorescent material. By measuring the fluorescence, a 5.6×4.9 μm2 focal spot was observed in situ. Fluorescence was used to measure the saturable absorption of VUV pulses in the tin layer. The transmission increases nonlinearly higher with increasing laser intensity. [ABSTRACT FROM AUTHOR]

In this article, the authors comment on the research conducted by R. Krischek and colleagues which reports the use of an spontaneous parametric down-conversion (SPDC) nonlinear crystal inside a passive optical cavity designed to dramatically enhance the power of the ultra-violet (UV) femtosecond laser pulses needed for the down-conversion process. They opine the work demonstrates an important application of UV femtosecond enhancement cavities (fsECs) to applications in ultrafast nonlinear optics.