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We report on the design, fabrication, and characterization of single longitudinal mode InAs/GaAs quantum dot lasers emitting at the 1.3 µm communication band. The influence of simply etched surface high-order gratings in the ridge of the Fabry-Perot lasers has been studied. A 35th-order surface grating is fabricated by standard photolithography to introduce the refractive index perturbation, which leads to the reduced mirror loss at the desired wavelength and thus realizing single longitudinal mode lasing. Stable single-mode operations are maintained at the injection current range of 45-100 mA with a side-mode suppression ratio up to 33 dB.Developments toward the implementation of a terahertz pulse imaging system within a guided reflectometry configuration are reported. Two photoconductive antennas patterned on the same LT-GaAs active layer in association with a silica pipe hollow-core waveguide allowed us to obtain a guided optics-free imager. Selleckchem A1874 Besides working in a pulsed regime, the setup does not require additional optics to focus and couple the terahertz pulses into the waveguide core, simplifying the global implementation in comparison with other reported guided terahertz reflectometry systems. The system is qualified for imaging purposes by means of a 1951 USAF resolution test chart. An image resolution, after a 53 mm propagation length, by about 0.707 LP/mm over the 400-550 GHz integrated frequency band, was obtained, thus providing a promising basis to pursue efforts toward compact guided pulse imagers for sample inspection within the terahertz range.A method of extending the imaging range through scattering layers around a reference point (RP) is realized. Objects within the entire correlation range of the RP can be totally recovered. By scanning the light source, objects within the memory effect (ME) range of the RP are completely recovered with high quality. By combining the shift of a camera to move the object to the center of observation view, objects far away from the RP are retrieved with an improved signal-to-noise ratio. The extended imaging range is about 3.5 times the ME range and more than 16 times the imaging range with normal static illumination. The RP can be imprecisely placed at a distance from the objects instead of precisely replacing them owing to the extended imaging range. This simple-system method forcefully breaks the limitation of the ME range and is very easy to implement in practical applications, which is meaningful for the research in scattering imaging.This paper proposes and studies the characteristics of a laser-driven optothermal microactuator (OTMA) directly operated in water. A theoretical model of optothermal temperature rise and expansion is established, and simulations on a 1000 µm long OTMA are conducted, revealing that its arm is able to expand and contract in response to the laser pulses in a water environment. Microactuating experiments are further carried out using a microfabricated OTMA. The results demonstrate that the OTMA can be practically actuated in water by a 650 nm laser beam and that the OTMA's deflection amplitude increases linearly with laser power. When irradiated by laser pulses with 9.9 mW power and 0.9-25.6 Hz frequencies, the OTMA achieves deflection amplitude ranging from 3.9 to 3.2 µm, respectively. The experimental results match well with theoretical model when taking the damping effect of water into account. This research may be conducive to developing particular micro-electromechanical systems or micro-optoelectromechanical devices such as underwater optothermal micromotors, micro-pumps, micro-robots, and other underwater microactuators.Geometric phase retarders-such as q-plates and S-waveplates-have found wide applications due to simplicity of operational principles and flexibility for the generation of azimuthally symmetric polarization states and optical vortices. Ellipticity of the polarization vector and phase of the generated beam strongly depend on the retardation of the plate. Real devices usually have retardation value slightly different than the nominated one. Previously unattended perturbation of the retardation leads to asymmetry in intensity distribution and variation of ellipticity of the local polarization vector of the generated beam. We elucidate that controlled and intentionally driven azimuthally variable, oscillating perturbation of the retardation reveals the possibility to avoid distortions in the generated beam and leads to the recovery of the symmetrically distributed intensity and polarization (with zero ellipticity) of the beam. Described recovery of the desired polarization state could find application for generation of the high purity beam with azimuthally symmetric polarization, in which the local polarization ellipse has zero ellipticity.In this paper, we report the performance of a bismuth-doped fiber amplifier at 1687 nm. This wavelength region is particularly interesting for laser-based spectroscopy and trace gas detection. The active bismuth-doped fiber is pumped at 1550 nm. With less than 10 mW of the seed power, more than 100 mW is obtained at the amplifier's output. We also investigate the signal at the output when a wavelength-modulated seed source is used, and present wavelength modulation spectroscopy of methane transition near 1687 nm. A significant baseline is observed in the spectra recorded when the fiber amplifier is used. The origin of this unwanted background signal is discussed and methods for its suppression are demonstrated.In the method of surface reconstruction from polarization, the reconstructed area is generally non-rectangular and contains a large number of sampling points. There is a difficulty that the coefficient matrix in front of the height vector changes with the shape of the measured data when using the zonal estimation. The traditional iterative approaches consume more time for the reconstruction of this type of data. This paper presents a non-iterative zonal estimation to reduce the computing time and to accurately reconstruct the surface. The index vector is created according to the positions of both the valid and invalid elements in the difference and gradient matrices. It is used to obtain the coefficient matrix corresponding to the general data. The heights in the non-rectangular area are calculated non-iteratively by the least squares method. At the same time, the sparse matrix is applied for handling the large-scale data quickly. The simulation and the experiment are designed to verify the feasibility of the proposed method.
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