Silverralston0788

Transverse optical confinement in oxide-confined vertical-cavity surface-emitting lasers (VCSELs) crucially depends on thickness of oxide layer and its position relative to a standing wave. Modifying the structure reduces the overlap between the oxide layer and the standing wave as well as effective refractive index difference between core and cladding of the VCSEL that subsequently decreases of the number of transverse modes and increases the mode extension beyond oxide aperture. A 795 nm VCSEL is designed and fabricated with this concept. The proposed device achieves high single-mode operation of 4.1 mW at 80 °C, SMSR of 41.68 dB, and OPSR of 27.4 dB. VCSEL is applied in a nuclear magnetic resonance gyroscope (NMRG) system as pump source due to its excellent device performance and satisfactory test results are obtained.Stokes lenses are variable power astigmatic lenses comprising of, in its standard version, two pure cylindrical lenses of equal but contrary power that rotate in opposite directions. Here, we present an optical device with variable and continuous astigmatic power which is based on a modified Stokes lens where two sphero-cylindrical lenses (in the form of pure astigmatic lenses) are combined in the classical way but merged with another fixed pure astigmatic lens for improving the capabilities of the resulting optical device concerning the expansion of the astigmatic range without worsening the dioptric power step resolution. The performance of this device is theoretically analyzed in virtue of the power vectors formalism including a three-dimensional (3-D) representation of the generated dioptric power as a function of both the meridian and the rotation angle between the cylinder's axes. In addition, we have assembled a lab-made prototype of the proposed modified Stokes lens and validated its theoretical behavior by dioptric power measurements with an automatic focimeter. As conventional Stokes lenses, the applications of this new optical device range from astigmatism compensation in optical instruments to measurement of refractive error in subjective routines with the previously commented improved capabilities.Ultrasound detection via optical resonators can achieve high levels of miniaturization and sensitivity as compared to piezoelectric detectors, but its scale-up from a single detector to an array is highly challenging. While the use of wideband sources may enable parallel interrogation of multiple resonators, it comes at the cost of reduction in the optical power, and ultimately in sensitivity, per channel. In this work we have developed a new interferometric approach to overcome this signal loss by using high-power bursts that are synchronized with the time window in which ultrasound detection is performed. Each burst is composed of a train of low-noise optical pulses which are sufficiently wideband to interrogate an array of resonators with non-overlapping spectra. We demonstrate our method, termed burst-mode pulse interferometry, for interrogating a single resonator in which the optical power was reduced to emulate the power loss per channel that occurs in parallel interrogation of 20 to 200 resonators. The use of bursts has led to up 25-fold improvement in sensitivity without affecting the shape of the acoustic signals, potentially enabling parallel low-noise interrogation of resonator arrays with a single source.By studying the nonlinear absorption of ultrafast laser pulses in fused silica, we examine, both with experiments and numerical simulations, the different polarization dependence of multiphoton ionization and avalanche ionization. Results show multiphoton ionization and avalanche ionization play different roles in femtosecond and picosecond laser micromachining, and the contribution via avalanche ionization increases with pulse duration. Meanwhile, the spatial distribution of the free carriers generated by circularly polarized pulses is more concentrated than those generated by linear polarization for picosecond laser pulses. These properties make the circular polarized ultrafast laser a possible way to improve the ultrafast laser micromachining efficiency and spatial quality, and can help to reduce some problematic nonlinear effects in ultrafast laser micromachining of low energy band materials.For the requirement of high-precision vertical profile of the polarization and optical properties of natural seawater, a ship-borne variable-FOV, dual-wavelength, polarized ocean lidar system is designed to obtain the volume linear depolarization ratio (VDR), color ratio and optical parameter profiles of seawater. Bempedoic With the high signal-to-noise ratio, which benefits from the high power (355 nm with 120 mJ, 532 nm with 200 mJ) solid-state laser and a photon counting recorder with a sampling rate of 1 GHz, the attenuated backscattered signal of seawater in the western Pacific campaign reaches to the depth of 50 m, where a plankton layer presents. The receiver of lidar is capable of switching to wide and narrow field of view (FOV), respectively, to obtain the lidar attenuation coefficient Klidar, which is in good agreement with the beam attenuation coefficient of seawater c with a narrow FOV and diffuse attenuation coefficient Kd with a wide FOV. Besides, the Klidar, and the VDR, at two wavelengths of 355 nm and 532 nm are compared to explore the possibility of multi-wavelength of laser application in the ocean lidar. The VDR and the color ratio profiles have a desirable correlation with the in-situ measurement of chlorophyll a (Chla) and chromophoric dissolved organic matter (CDOM) profiles, respectively. With the combination of the Klidar, the VDR and the color ratio profiles, measured in different regions and time periods during the campaign, the multi-wavelength and polarization lidar shows its potential to explore various ocean compositions, such as the ocean particles size shape, the species and vertical migration characteristics of planktons, and the profile distribution of the ocean compositions.In this work, two Faraday channels and one shadow channel are constructed by two non-polarizing beam splitters and one reflector to measure the Faraday rotation distribution. The intensity of the Faraday and shadow images is related to the state of polarization (SOP) of the incident light, thus achieving two-dimensional accurate measurement. The measurement sensitivity is influenced by the settings of two polarization analyzers in the Faraday channels and the parameters of beam splitters, which are explored numerically and verified with experiments. The fluctuation of the probe light is eliminated by using three evaluation indexes. Also, the measurement range and error sources under different experimental settings are discussed.X-ray tomography is widely used for three-dimensional structure determination in many areas of science, from the millimeter to the nanometer scale. The resolution and quality of the 3D reconstruction is limited by the availability of alignment parameters that correct for the mechanical shifts of the sample or sample stage for the images that constitute a scan. In this paper we describe an algorithm for marker-free, fully automated and accurately aligned and reconstructed X-ray tomography data. Our approach solves the tomographic reconstruction jointly with projection data alignment based on a rigid-body deformation model. We demonstrate the robustness of our method on both synthetic phantom and experimental data and show that our method is highly efficient in recovering relatively large alignment errors without prior knowledge of a low resolution approximation of the 3D structure or a reasonable estimate of alignment parameters.Nonlinear optical gain modulation (NOGM) is a method to generate high performance ultrafast pulses with wavelength versatility. Here we demonstrate coherent femtosecond Raman pulse generation through cascaded NOGM process experimentally. Two single-frequency seed lasers (1121 and 1178 nm) are gain-modulated by 117 nJ 1064 nm picosecond pulses in a Raman fiber amplifier. Second-order (1178 nm) Stokes pulses are generated, which have a pulse energy of 76 nJ (corresponding to an optical conversion efficiency of 65%) with a pulse duration of 621 fs (after compression). Dynamic evolution of both pump and cascaded Stokes pulses within the Raman amplifier are investigated by numerical simulations. The influences of pump pulse duration and energy are studied in detail numerically. Moreover, the simulations reveal that NOGM pulses with higher energy and shorter pulse duration could be obtained by limiting the impact of walk-off effect between pump and Raman pulses. This approach can offer a high energy and wavelength-agile ultrafast source for various applications such as optical metrology and biomedical imagining.The ability to identify the contents of a sealed container, without the need to extract a sample, is desirable in applications ranging from forensics to product quality control. One technique suited to this is inverse spatially offset Raman spectroscopy (ISORS) which illuminates a sample of interest with an annular beam of light and collects Raman scattering from the center of the ring, thereby retrieving the chemical signature of the contents while suppressing signal from the container. Here we explore in detail the relative benefits of a recently developed variant of ISORS, called focus-matched ISORS. In this variant, the Fourier relationship between the annular beam and a tightly focused Bessel beam is exploited to focus the excitation light inside the sample and to match the focal point of excitation and collection optics to increase the signal from the contents without compromising the suppression of the container signal. Using a flexible experimental setup which can realize both traditional and focus-matched ISORS, and Monte-Carlo simulations, we elucidate the relative advantages of the two techniques for a range of optical properties of sample and container.Red-green color vision deficiency (CVD) is the most common single locus genetic disorder in humans, affecting approximately 8% of males and 0.4% of females [G. H. M. Waaler, Acta Ophthalmol.5, 309 (2009)10.1111/j.1755-3768.1927.tb01016.x]; however, only about 1/4 of CVD individuals are dichromats who rely on only two cone types for color vision. The remaining 3/4 are anomalous trichromats whose CVD is milder, being based on three cone types, and who still perform remarkably well on many color-based tasks. To illustrate this, we have developed an algorithm that computes the relative loss of color discrimination in red-green CVD individuals with varying degrees of deficiency and accurately simulates their color experience for color normal observers. The resulting simulation illustrates the large gap in color discrimination between dichromats and even the most severe anomalous trichromats, showing that, relative to dichromats, the majority of anomalous trichromats can function without aids for color vision deficiency.High-frequency ultrasound sensors are essential for high-resolution medical ultrasonic imaging and industrial ultrasonic non-destructive monitoring. In this paper, we propose highly sensitive broadband ultrasound sensors based on fused dual-core chalcogenide-polymethyl methacrylate (As2Se3-PMMA) microfibers. We demonstrate that ultrasound response is determined by the differential slope of transmission spectra in the dual-core microfiber, which is verified by detecting the acoustic response in various microfibers of different tapering parameters. A broadband ultrasound frequency range with a high signal-to-noise ratio (SNR) is achieved in the fused dual-core microfiber (DCM) with a sub-micron core diameter and a close core separation due to the large spectral slope at the quadrature points of the transmission spectrum. In addition, we experimentally demonstrate the sensing of ultrasound waves propagating with and without an aluminum plate in the DCM sensor. An ultrasound sensor with a broadband frequency range from 20 kHz to 80 MHz and an average SNR of 31 dB is achieved in a compact fused dual-core As2Se3-PMMA microfiber when it is directly placed on a piezoelectric transducer (PZT).