Narrow Laser Beam Research Articles

Under Sea Laser Communications Field Demonstration in Narrow-Beam

In this paper described that the narrow beam laser correspondence through the waters Island. The transmitter and receiver were mounted on an aluminum truss and set in the water. The transmitter comprised of a constant modulator and encoder, a 515 nm wavelength business laser, collimating optics, and a directing mirror. The collector incorporated a guiding mirror, a central plane camera, a straight mode torrential slide photograph diode (APD), a photograph multiplier tube (PMT) single photon finder, a huge range imaging camera, an iris to shift the field of view, optics to part the pillar between the different identifiers, and field-programmable door exhibit (FPGA) hardware for continuous demodulation and disentangling. The PMT and APD locators were utilized for correspondences showings; the imaging and central plane cameras were utilized for channel portrayal estimations and framework arrangement. Interchanges and portrayal information were gathered through an assortment of conditions over the five day field try, including day and night, quiet and high winds, and surge and ebb tide. In the examination, the transmit control; beneficiary field of view, and connection separation were shifted. The water transmission actiivity and volume scrambling capacity were measured all through the test to adjust the outcomes. Continuous correspondences shows with the PMT were completed between 1 megabit-per-second (Mbps) and 8.7 Mbps at 7.8 meters, which spoken to in the vicinity of 8 and 12 shaft eradication lengths. With the APD, 125 Mbps were exhibited at 4.8 meters, speaking to around 5 annihilation lengths.

Post-Newtonian equations of motion for LEO debris objects and space-based acquisition, pointing and tracking laser systems

This paper deals with the problem of throwing middle-sized low Earth orbit debris objects into the atmosphere via laser ablation. The post-Newtonian equations here provided allow (hypothetical) space-based acquisition, pointing and tracking systems endowed with very narrow laser beams to reach the pointing accuracy presently prescribed. In fact, whatever the orbital elements of these objects may be, these equations will allow the operators to account for the corrections needed to balance the deviations of the line of sight directions due to the curvature of the paths the laser beams are to travel along. To minimize the respective corrections, the systems will have to perform initial positioning manoeuvres, and the shooting point-ahead angles will have to be adapted in real time. The enclosed numerical experiments suggest that neglecting these measures will cause fatal errors, due to differences in the actual locations of the objects comparable to their size.

On Divergence-Angle Efficiency of a Laser Beam in Free-Space Optical Communications for High-Speed Trains

We compare narrow and wide laser beams in a free-space optical (FSO) communications system for high-speed train communications and analyze the tradeoffs among the received power, coverage area, and the complexity of the acquisition-tracking-pointing (ATP) mechanism. We propose to employ a divergence angle of a wide beam in the range [0.07 $^{\circ }$ , 2.002 $^{\circ }$ ] to relax the steering speed of the fast steering mirror, which is a major component of the ATP mechanism in an FSO transceiver. In addition, we overcome the negative effects of train vibrations by using a proposed divergence-angle range for a wide beam. The proposed range of divergence angles provides a large link range and effective coverage length, and contact time as compared to a narrow beam.

Scanning Laser Ophthalmoscopy

The aim of retinal imaging techniques is visualization of morphological changes at the cellular and tissue level. Various techniques are used for this purpose. The scanning laser ophthalmoscopy (SLO), a retinal optical imaging device based on standard scanning laser microscopy is an imaging technique that scans the fundus with a highly collimated narrow laser beam and measures the backscattered light intensity. Here, progress on developing SLO instruments and their applications in ophthalmology are reviewed.

Autonomous shooting at middle size space debris objects from space-based APT laser systems

This paper is motivated by the need of removing middle size space debris objects. It deals with the problem of increasing the pointing accuracy while shooting at these objects by means of autonomous space-based APT systems endowed with very narrow laser beams. It is shown that shooting at these objects with these systems is the one single ballistic problem that becomes singular in space. This means that the shooting direction that is to be implemented by any of these systems to reach an object at a given instant can only be hopefully implemented after the object has been previously reached. Thus, the problem becomes backwards recurrent with no end for any object–system configuration, except when the LOS direction remains constant for some period of time. It is also shown that the implementation of the point-ahead angles from the data acquired prior to the respective shootings is essential to keep accuracy. In fact, one single omission during the action may cause errors larger than the size of the objects. As a consequence, we find that there is only one way for an autonomous system to minimize the pointing errors: any shooting sequence to any of these objects must be started when the transverse component of the relative velocity of the object with respect to the system is zero (actually, as close to zero as possible).

Realization of low power-laser induced thermionic emission from Ag nanoparticle-decorated CNT forest: A consequence of surface plasmon resonance

Enhancement of electron emission from Ag nanoparticle-decorated carbon nanotube (CNT) forest, using low power-lasers, is reported in this work. Realization of thermionic emission from CNTs using the low power laser can be achievable when the CNT forest is illuminated by a narrow laser beam which leads to localized heating of the CNT forest surface. For this purpose, CNT forest was decorated with Ag nanoparticles. Surface plasmon resonance of Ag nano-particles led to intense local electric field which is responsible for localized heating and thermionic emission from CNTs. Enhancement of emission current from CNTs depends on the wavelength of the excitation laser, so that matching the wavelength of laser to the wavelength of the plasmon resonance leaded to a maximum enhancement in electron emission.

Highly integrated optical phased arrays: photonic integrated circuits for optical beam shaping and beam steering

Abstract Technologies for efficient generation and fast scanning of narrow free-space laser beams find major applications in three-dimensional (3D) imaging and mapping, like Lidar for remote sensing and navigation, and secure free-space optical communications. The ultimate goal for such a system is to reduce its size, weight, and power consumption, so that it can be mounted on, e.g. drones and autonomous cars. Moreover, beam scanning should ideally be done at video frame rates, something that is beyond the capabilities of current opto-mechanical systems. Photonic integrated circuit (PIC) technology holds the promise of achieving low-cost, compact, robust and energy-efficient complex optical systems. PICs integrate, for example, lasers, modulators, detectors, and filters on a single piece of semiconductor, typically silicon or indium phosphide, much like electronic integrated circuits. This technology is maturing fast, driven by high-bandwidth communications applications, and mature fabrication facilities. State-of-the-art commercial PICs integrate hundreds of elements, and the integration of thousands of elements has been shown in the laboratory. Over the last few years, there has been a considerable research effort to integrate beam steering systems on a PIC, and various beam steering demonstrators based on optical phased arrays have been realized. Arrays of up to thousands of coherent emitters, including their phase and amplitude control, have been integrated, and various applications have been explored. In this review paper, I will present an overview of the state of the art of this technology and its opportunities, illustrated by recent breakthroughs.

A Real-Time Orbit Determination Method for Smooth Transition from Optical Tracking to Laser Ranging of Debris.

A critical requirement to achieve high efficiency of debris laser tracking is to have sufficiently accurate orbit predictions (OP) in both the pointing direction (better than 20 arc seconds) and distance from the tracking station to the debris objects, with the former more important than the latter because of the narrow laser beam. When the two line element (TLE) is used to provide the orbit predictions, the resultant pointing errors are usually on the order of tens to hundreds of arc seconds. In practice, therefore, angular observations of debris objects are first collected using an optical tracking sensor, and then used to guide the laser beam pointing to the objects. The manual guidance may cause interrupts to the laser tracking, and consequently loss of valuable laser tracking data. This paper presents a real-time orbit determination (OD) and prediction method to realize smooth and efficient debris laser tracking. The method uses TLE-computed positions and angles over a short-arc of less than 2 min as observations in an OD process where simplified force models are considered. After the OD convergence, the OP is performed from the last observation epoch to the end of the tracking pass. Simulation and real tracking data processing results show that the pointing prediction errors are usually less than 10″, and the distance errors less than 100 m, therefore, the prediction accuracy is sufficient for the blind laser tracking.

Gradient scattered light method for non-destructive stress profile determination in chemically strengthened glass

A new non-destructive gradient scattered light method is presented for micron-scale stress profile measurement in chemically strengthened (chemically tempered, ion exchanged) glass. Direct non-destructive stress measurement in the surface layer (<100 µm) of chemically strengthened glass is reported for the first time. This is accomplished by passing a narrow laser beam through the surface layer of the glass at a considerably large incidence angle of 81.9°. The theory of gradient scattered light method is based on the ray tracing of ordinary and extraordinary rays in chemically strengthened glass and calculating the optical retardation distribution along the curved ray path. The experimental approach relies on recording the scattered light intensity and calculating the optical retardation distribution from it. The stress profile is measured in a chemically strengthened (8 h at 480 °C in a salt mixture of 80 mol% KNO3 and 20 mol% NaNO3) lithium aluminosilicate glass plate to illustrate the capability of the method. Measured surface compressive stress was −1053 MPa and case depth 365 µm. Method is validated with transmission photoelasticity. The method could also be used for stress profile measurement in all transparent flat materials (such as very thin thermally tempered glass slabs or polymers). Additional new applications could be: (1) enhanced version of Bradshaw’s surface layer etching method for stress profile measurement in case of ultra-thin case depths <20 µm; (2) micron-scale non-destructive tomography of layered polymeric gradient-refractive-index materials. The experimental procedure is developed to the level of full automation and the measurement time is less than 10 s.

Photonic waveguide structures in photorefractive lithium niobate with pyroelectric mechanism of nonlinear response

Compensation for the nonlinear diffraction of narrow laser beams with wavelengths of 532 and 633nm and the formation of photonic waveguides and waveguide circuits due to the contribution of pyroelectric effect to the nonlinear response of lithium niobate crystal have been experimentally demonstrated. Complete compensation for the linear and nonlinear diffraction broadening of light beams is obtained upon uniform heating of an undoped sample from room temperature to 55◦C.

Fade-resistant photochromic reactions in a self-healable polymer.

Molecular diffusion in a polymer matrix was studied to prevent degradation of photochromic reactions during repeated coloration-decoloration processes. Photochromic diarylethene was dispersed in polydimethylsiloxane (cured polymer), since it promoted exchange of damaged and fresh molecules owing to high diffusivity. The diffusion coefficient was evaluated by measuring a distribution of dye molecules that were colored within a narrow laser beam path. Temporal change of the distribution fitted well to theoretical curves that were drawn according to the 2-D solutions of Fick's equation. The experimental results indicated a fifteen-fold enhancement of the diffusion coefficient (0.0015 mm(2)/s) when the polymer was swollen with toluene. Fading of this photochromic polymer was examined by repeating alternative irradiation of violet and green laser beams. Although a non-swollen polymer faded seriously within 1,000 photochromic cycles, a swollen polymer exhibited an excellent photochromic function even after 30,000 cycles.

Optical runaway evaporation for the parallel production of multiple Bose-Einstein condensates

We report on parallel production of Bose-Einstein condensates (BECs) in steerable, multi-plexed crossed optical dipole traps. Using a conventional trap-weakening evaporation scheme, where the optical trapping power is lowered, we obtain an array of up to four independent BECs. To improve evaporation efficiency, we propose to target each crossed trap site with a narrow auxiliary laser beam, creating an escape channel for energetic atoms. We experimentally demonstrate runaway evaporation using this scheme, which is characterized by very modest weakening in atomic confinement such that high densities and elastic collision rates can be maintained. Based on discretely time-shared optical tweezers, our approach is particularly suited for addressing the problem of simultaneously cooling atoms in multiple traps clouds, providing the freedom to act locally and in a tailored fashion at individual trap sites.

Raman spectroscopy of solutions and interfaces containing nitrogen dioxide, water, and 1,4 dioxane: evidence for repulsion of surface water by NO2 gas.

The interaction of water, 1,4 dioxane, and gaseous nitrogen dioxide, has been studied as a function of distance measured through the liquid-vapour interface by Raman spectroscopy with a narrow (<0.1 mm) laser beam directed parallel to the interface. The Raman spectra show that water is present at the surface of a dioxane-water mixture when gaseous NO2 is absent, but is virtually absent from the surface of a dioxane-water mixture when gaseous NO2 is present. This is consistent with recent theoretical calculations that show NO2 to be mildly hydrophobic.

Free Space Communications With Beam Steering a Two-Electrode Tapered Laser Diode Using Liquid-Crystal SLM

A free space optical wireless communication system with 3 degree angular coverage and 1.25 GHz modulation bandwidth is reported, in which relatively narrow laser beam of a simultaneous high power, high modulation speed and ultra high modulation efficiency directly modulated two-electrode tapered laser diode is steered using a nematic phase-only Liquid-Crystal On Silicon Spatial Light Modulator (LCOS SLM) by displaying reconfigurable 256 phase level gratings.

Theory of microdroplet and microbubble deformation by Gaussian laser beam

The theory for linear deformations of fluid microparticles in a laser beam of Gaussian profile is presented, when the beam focus is at the particle center as in optical trapping. Three different fluid systems are considered: water microdroplet in air, air microbubble in water, and a special oil-emulsion in water system used in experiments with optical deformation of fluid interfaces. We compare interface deformations of the three systems when illuminated by wide (compared to particle radius) and narrow laser beams and analyze differences. Deformations of droplets are radically different from bubbles under otherwise identical conditions, due to the opposite lensing effect (converging and diverging, respectively) of the two; a droplet is deformed far more than a bubble, cetera paribus. Optical contrast is found to be of great importance to the shape obtained when comparing the relatively low-contrast oil-emulsion system to that of water droplets. We finally analyze the dynamics of particle motion when the laser beam is turned on, and compare a static beam to the case of a short pulse. The very different surface tension coefficient implies a very different time scale for dynamics: microseconds for the water&#x2013;air interface and tens of milliseconds for the oil-emulsion. Surface oscillations of a water microdroplet are found always to be underdamped, while those of the oil-emulsion are overdamped; deformations of a microbubble can be either, depending on physical parameters.

In-vitro study of the temperature dependence of the optoacoustic conversion efficiency in biological tissues

The applicability of the optoacoustic (OA) method for monitoring temperature during thermal impact on biological tissues is studied experimentally. Tissues under study were chicken breast (as a model of muscle), porcine lard (as a model of fatty tissue) and porcine liver (as a model of richly perfused tissue). The temperature dependences of the amplitude of the OA signals excited in biological tissues were measured in-vitro in the temperature range of 20 — 80 °C under the narrow laser beam conditions. Measurements were performed in two regimes: during heating and cooling. Similarities and differences in the behaviour of the dependences in different temperature ranges associated with different structural composition of the samples were obtained. The accuracy of temperature reconstruction from experimental data for the investigated tissue types was evaluated. It is shown that during tissue coagulation its temperature can be determined with an accuracy of about 1 °C.

Study on the Simulation of the APT Rough Tracing System Based on the Predictive Control Technology

Laser space offers an attractive alternative in the military fields for its many advantages of wide bandwidth, high code rate, low power consumption and large capacity. Because the narrow laser beam will lead to many challenges in laser beam pointing, therefore, APT (acquisition, pointing and tracking) technology is one of key technology for the laser space communication. The ATP rough tracing servo turntable studied in this paper adopts two-axes-four-frame structure. In order to increase the tracking precision, the predictive control algorithm is adopted in the rough tracking position loop. The simulation result shows that, comparing with common PI controller, the predictive control algorithm could improve the dynamic response characteristics of the system and increase the tracking precision.

Narrowing of the coherent population trapping resonance under zone pumping in cells with different characteristics of the wall coating

It is shown that when coherent population trapping (CPT) resonance is excited by a narrow laser beam, the presence of elastic collisions with the cell wall significantly affects the line shape of the CPT-resonance. We have constructed a theoretical model, which is based on averaging over the random Ramsey sequences of the atom dwell time in the beam and dark zones and takes into account the probability of elastic bounce of an atom from the wall.

Temperature dependence of the optoacoustic transformation efficiency in ex vivo tissues for application in monitoring thermal therapies

The calibration dependencies of the optoacoustic (OA) transformation efficiency on tissue temperature are obtained for the application in OA temperature monitoring during thermal therapies. Accurate measurement of the OA signal amplitude versus temperature is performed in different ex vivo tissues in the temperature range 25°C to 80°C. The investigated tissues were selected to represent different structural components: chicken breast (skeletal muscle), porcine lard (fatty tissue), and porcine liver (richly perfused tissue). Backward mode of the OA signal detection and a narrow probe laser beam were used in the experiments to avoid the influence of changes in light scattering with tissue coagulation on the OA signal amplitude. Measurements were performed in heating and cooling regimes. Characteristic behavior of the OA signal amplitude temperature dependences in different temperature ranges were described in terms of changes in different structural components of the tissue samples. The accuracy of temperature reconstruction from the obtained calibration dependencies for the investigated tissue types is evaluated.

Beam displacement as a function of temperature and turbulence length scale at two different laser radiation wavelengths

Narrow laser beams directed from aircraft may at times pass through the exhaust plume of the engines and potentially degrade some of the laser beam characteristics. This paper reports on controlled studies of laser beam deviation arising from propagation through turbulent hot gases, in a well-characterized laboratory burner, with conditions of relevance to aircraft engine exhaust plumes. The impact of the temperature, laser wavelength, and turbulence length scale on the beam deviation has been investigated. It was found that the laser beam displacement increases with the turbulent integral length scale. The effect of temperature on the laser beam angular deviation, σ, using two different laser wavelengths, namely 4.67 μm and 632.8 nm, was recorded. It was found that the beam deviation for both wavelengths may be semiempirically modeled using a single function of the form, σ=a(b+(1/T)(2))(-1), with two parameters only, a and b, where σ is in microradians and T is the temperature in °C.