Laser Beam Propagation Research Articles

Directed high-energy infrared laser beams for photovoltaic generation of electric power at remote locations

Transferring energy without transferring mass is a powerful paradigm to address the challenges faced when the access to, or the deployment of, the infrastructure for energy conversion is locally impossible or impractical. Laser beaming holds the promise of effectively implementing this paradigm. With this perspective, this work evaluates the optical-to-electrical power conversion that is created when a collimated laser beam illuminates a silicon photovoltaic solar cell that is located kilometers away from the laser. The laser is a CW high-energy Yb-doped fiber laser emitting at a center wavelength of 1075 nm with ∼1 m2 of effective beam area. For 20 kW illumination of a solar panel having 0.6 m2 of area, optical simulations and thermal simulations indicate an electrical output power of 3000 W at a panel temperature of 550 K. Our investigations show that thermo-radiative cells are rather inefficient. In contrast, an optimized approach to harvest laser energy is achieved by using a hybrid module consisting of a photovoltaic cell and a thermoelectric generator. Finally, practical considerations related to infrared power beaming are discussed and its potential applications are outlined.

Stacked Polarizing Elements for Controlling Parameters of Surface Relief Gratings Written in Photosensitive Materials.

Photosensitive materials are widely used for the direct fabrication of surface relief gratings (SRGs) without the selective etching of the material. It is known that the interferometric approach makes it possible to fabricate SRGs with submicron and even subwavelength periods. However, to change the period of the written SRGs, it is necessary to change the convergence angle, shift a sample, and readjust the interferometric setup. Recently, it was shown that structured laser beams with predetermined, periodically modulated polarization distributions can also be used to fabricate SRGs. A structured laser beam with the desired polarization distribution can be formed with just one polarizing optical element-for example, the so-called depolarizer, a patterned micro-retarder array. The use of such stacked elements makes it possible to directly control the modulation period of the polarization of the generated laser beam. We show that this approach allows one to fabricate SRGs with submicron periods. Moreover, the addition of q-plates, elements effectively used to generate cylindrical vector beams with polarization singularities, allows the efficient formation of fork polarization gratings (FPGs) and the fabrication of higher-order fork-shaped SRGs. Full control of the parameters of the generated FPGs is possible. We demonstrate the formation of FPGs of higher orders (up to 12) by only adding first- and second-order q-plates and half-wave plates to the depolarizers. In this work, we numerically and experimentally study the parameters of various types of SRGs formed using these stacked polarizing elements and show the significant potential of this method for the laser processing of photosensitive materials, which often also serve as polarization sensors.

Analysis of misaligned optics effects on beam pointing stability in dual-pass optical system

The high-power laser device utilizes a multi-pass amplification system to achieve elevated power laser output. Laser beam is transmitted several times through the amplifier, and the pointing stability is a critical factor affecting the efficiency of the system. Any perturbation of the optics during laser transmission can cause misalignment and further lead to beam pointing errors. Laser beam propagation simulation was conducted using the ray tracing method. Equivalent experiment was performed using a laser with a wavelength of 532 nm, and the centroid position data of the laser beam were collected to characterize the effect of the optics misalignment on laser pointing. A model evaluating the sensitivity of the optics was constructed, and the analysis of how various optics impact pointing accuracy was conducted. Results indicate that, a linear relationship exists between the misalignment of the optic and the pointing shift and angular deviation of the beam when a single optic is misaligned. If multiple optics are misaligned, the shift in centroid position of the laser beam can be calculated by adding up the shifts caused by each misaligned optic. Furthermore, the shift in the centroid position of the laser beam is the linear superposition of the misalignment of each optic.

Resonant second-harmonic generation of self-focused oblique incident laser beam in plasma

The present manuscript aims to realize the effect of self-focusing on second-harmonic generation (SHG) by oblique incident laser beams in plasma. When an intense laser beam is obliquely incident on the plasma, it is resolved into reflected and refracted components, and resonant SHG is produced in the reflected component on account of the self-focusing of the incident laser. With the help of paraxial approximation, we have obtained a mathematical expression for the beam width parameter and for the normalized amplitude of the second harmonic. It has been observed that the amplitude of the second-harmonic pulse is significantly influenced by the intensity of the incident laser beam, the wiggler magnetic field, and the normalized plasma frequency. The analysis was performed for different values of the angle of incidence and laser parameters. The results show stronger self-focusing and, hence, efficient SHG when the angle of incidence is the critical angle.

A modification to the extended Rytov theory

This paper proposes a heuristic modification to the extended Rytov theory of strong scintillation [Andrews L, Phillips R. Laser beam propagation through random media. 2nd ed., Washington, USA: SPIE Press; 2005, Andrews LC, Al-Habash MA, Hopen CY, et al. Theory of optical scintillation: Gaussian-beam wave model. Waves Random Media. 2001;11(3):271–291]. This is done by dividing the large and small scales in the extended Rytov theory into further sub-scales. Expressions for the induced irradiance variance, and log-irradiance, due to each sub-scale are presented. The modified theory is used to derive and justify recent results in irradiance fluctuation modeling and hence answer a question initially proposed in [Shishter YM, Young RC, Ali FH. Irradiance probability density function for turbulence induced fading in free space optics. JOSA A. 2022;39(7):1267–1274, Shishter YM, Young RC, Ali FH. General statistical model of irradiance fluctuations in free space optics. JOSA A. 2023;40(1):53–63]. Plots of the irradiance pdf under the modified theory are in support of the theory. The validity of the theory presented would result in modifications to the classical scintillation analysis of waves in random media, with applications to the design of optical systems. Moreover, it is observed that the mathematical framework developed also follows from the assumption of variations in the turbulence along a horizontal path. The work presented in this paper suggests the need of further theoretical and experimental investigations into the effect of variations in atmospheric turbulence characteristics along horizontal paths in the received signal irradiance distribution.

Coherent control of parametric generation of laser beams via intersubband transitions in quantum wells

This paper investigates the propagation dynamics of laser beams within a semiconductor quantum well (QW) system. The study explores various scenarios involving different detuning values and spatially varying incident beams. The light–matter interaction within the QW system shows a complex interplay between detuning, spatial characteristics, and beam properties. In the resonant case, where the detuning values for probe and signal beams are zero, we observe exponential relaxation of both beams reaching a common value. Introducing detuning leads to oscillatory behaviors, with larger detuning values promoting more pronounced oscillations and an enhanced signal beam. The investigation takes an intriguing turn when we consider position-dependent incident beams. In these cases, the spatial patterns of the initial beam are transferred to the generated beam, leading to soliton-like propagation and the creation of beams with specific spatial dependencies. Remarkably, under substantial detuning, both incident and generated beams adopt periodic patterns in two dimensions, forming lattice structures with spot-like peak intensities. These findings underscore the versatility and controllability of the QW system, offering opportunities for engineered spatial and spectral properties in laser beams.

PROPAGATION OF VECTOR VORTEX BEAMS EXCITED BY A TERAHERTZ LASER DIELECTRIC RESONATOR

In this paper, analytical expressions for the nonparaxial mode diffraction of a terahertz laser dielectric waveguide resonator are derived. It is assumed that the modes interact with a spiral phase plate. The cases of different topological charges (n) are considered. Also, using numerical simulations, the physical features of emerging vortex beams are studied when they propagate in free space. The Rayleigh-Sommerfeld vector theory is used to study propagation of the vortex laser beams in different diffraction zones excited by the modes of a dielectric waveguide quasi-optical resonator upon incidence on a spiral phase plate. It is shown that the interaction of a spiral phase plate with a linearly polarized EH<sub>11</sub> mode forms a ring (n = 1, 2) due to field structure with an intensity maximum at the center (n = 0). For the azimuthally polarized TE<sub>01</sub> mode, the ring (n = 0) field structure transforms into a field distribution with an intensity maximum at the center (n = 1) and then back to a ring (n = 2). In this case, the phase front of the EH<sub>11</sub> mode beam turns from a spherical shape to a spiral one with one singularity point on the axis, while a region with two singularity points appears off the axis for the phase structure of the TE<sub>01</sub> mode beam.

ПОШИРЕННЯ ТЕРАГЕРЦОВИХ ВИХРОВИХ ЛАЗЕРНИХ ПУЧКІВ У ВІЛЬНОМУ ПРОСТОРІ

Subject and Purpose. Currently, numerous ideas and different methods have been in growth for generating vortex beams — areas of the circular motion of the electromagnetic wave energy flow around the so-called phase singularity points caused by a violation of the wave front topological structure. The purpose of this work is to obtain analytical expressions describing the nonparaxial diffraction of wave modes of the waveguide resonator of a terahertz laser during the wave mode interaction with a spiral phase plate. The resulting vortex beams are examined for their physical features in free space propagation. Methods and Methodology. The Rayleigh-Sommerfeld vector theory is adopted to consider the propagation of vortex laser beams generated by wave modes of the quasi-optical waveguide cavity when interacting with a spiral phase plate in different diffraction zones. Results. For the first time, analytical expressions have been obtained to describe the nonparaxial diffraction of wave modes of the waveguide resonator of a terahertz laser, when resonator modes interact with a spiral phase plate at different topological charges, n. The physical features of the resulting vortex beams were studied in their free space propagation. It has been shown that a spiral phase plate modifies the structure of the linearly polarized EH₁₁ mode so that the original (n=0) intensity profile with the maximum energy at the center turns at n=1 and 2 into a ring-like donut shape with an energy hole in the center. The azimuthally polarized TE₀₁ mode has originally (n=0) a ring-shaped intensity. At n=1, this configuration changes to have the maximum intensity in the center. At n=2, it becomes annular again. In the process, the spherical phase front of the beam of the linearly polarized EH₁₁ mode becomes spiral and have one singularity point on the axis, whereas the phase structure of the azimuthally polarized TE₀₁ mode gains a region with two phase singularity points off the axis. Conclusions. The results of the study can effectively facilitate information transfer in high-speed THz communication systems. They can provide a real platform to perform tasks related to tomography, exploring properties of materials, detecting astrophysical sources, which makes them very promising in modern technologies.

Emulation and Testbed Prototyping of Laser Beam Propagation Characteristics through Atmospheric Turbulence for Optical Satellite Feeder Links

Two classical scenarios in space communications can be examined to evaluate the link performance of free space optical communications (FSO). These scenarios include the downlink and uplink between earth ground stations and near earth geostationary (GEO) satellites, as well as between the earth and spacecraft that are located a significant distance from the earth (i.e., one or more astronomical units (AU) away). Deep space is often defined as being more than 0.01 AU, or around 1,500,000 km, from Earth. In the first part of this analytical research, various practical system characteristics for optical lasers, telescopes, transmitters, receivers, and atmospheric disturbances, including absorption and scintillation, are taken into consideration. The simulation outcomes were compared to significant experimental data from DLR & JAXA’s OICETS/Kirari-Japan to validate the extended simulation model. Additionally, this work will propose a synthetic effects-based optical turbulence generator in order to deeply investigate atmospheric turbulence disturbances in free-space optical communication systems and support the advancement of artificial intelligence processing-based mitigation solutions. Worth mentioning, the initial outcomes and analytical comparisons demonstrate the preliminary viability of the simulation model for the link budget and scintillation estimation for FSO investigations, which can give deep insight into the development of the proposed testbed prototyping, machine learning-based laboratory measurement system, and enhancement possibility for FSO project design and execution for longand medium-term space mission planning.

Precision tailoring of laser beam propagation in a single crystalline diamond tool for in situ laser-assisted diamond turning.

The characteristics of laser beam propagation within a diamond tool critically influence the applied thermal softening capability of in situ laser-assisted diamond turning (In-LAT). In the present work, we perform optical geometric analysis, optical simulation and experimental validation to propose a novel diamond tool configuration for precisely tailoring laser beam propagation in In-LAT. First, the characteristics of laser beam propagation in the current In-LAT diamond tool are theoretically and experimentally explored. Second, according to the issues discovered in the current In-LAT diamond tool, an improved tool configuration based on the total internal reflection of a laser beam within the diamond tool is proposed, aiming for promoting refraction of the laser beam from the rake face of the diamond tool as well as eliminating the reflection of laser beam to tool holder. Finally, the optimization of laser beam incident position is carried out for achieving the superior profile and intensity of the emitted laser spot. Current work provides rational laser beam propagation for improving the thermal-softening capability of an In-LAT diamond tool.

Tunable vortex beams generation in visible band via Pr3+:YLF laser with a spot defect

The generation of optical vortex beams with user-configurable topological charge and spatial profile is a topic of intense research due to the numerous potential applications for these types of laser beams. In this work, we demonstrate the direct generation of vortex laser beams with controllable topological charge and tunable spatial profile from a Pr3+:YLF laser cavity using a spot-defect technique. A theoretical model is established to examine the relationship between the topological charge of the generated vortex beam and how this relates to laser cavity parameters. Experimentally, the selective operation of first- and second-order vortex beams and tunable optical vortex lattices with one to four singularities at 607 nm can be achieved by adjusting the position of the defect spot. This work offers insight into methods for the generation of visible optical vortex beams with controllable topological charge and tunable singularities for a range of applications.

Controllable multi-polarization laser beam generation and manipulation in a cylindrical cavity

The manipulation of spatial and polarization attributes in vector laser beams can be intricately controlled through a variety of methodologies including spatial light modulators, q-plates, optical cavities, and mode-selective coupling. Among these techniques, optical cavities exhibit notable merits as they enable the targeted amplification of desired polarization elements with significant efficiency and stability. This research article introduces a direct methodology to generate multiple polarized laser beams, leveraging a cylindrical laser cavity housing a birefringent c-cut Nd:YVO4 gain crystal. This technique facilitates the creation of Hermite-Gaussian modes exhibiting distinct polarization states. By exploiting specific geometrical arrangements involving optical Z-mode and W-mode, the degenerate laser cavity facilitates the concurrent production of numerous distinguishable elliptically and linearly polarized beams, obviating the necessity for supplementary optical components. Notably, this approach provides advanced control over the polarization of resulting beams through precise adjustments of pumping offset and cavity length. The polarization states are subjected to quantitative scrutiny through phase retardation analysis. This investigation introduces an innovative avenue for the generation of coherent multi-beams, thereby propelling progress across a wide spectrum of scientific and technological domains.

Study of convective air turbulence based on the probability distribution function of angle of arrival fluctuations

This study investigates the probability density function (PDF) of angle of arrival (AoA) fluctuations of a laser beam propagating through convective air turbulence in two settings: indoor turbulence and atmospheric surface layer. The indoor turbulence is generated by an electric heater with a 50 cm × 100 cm surface area placed horizontally on the bottom. The atmospheric turbulence experiments are conducted over a level at 60 cm height from an asphalted area using a slightly divergent laser beam that propagates along 350 m. Image motion monitoring of four sub-apertures installed in front of the receiving telescope aperture is used to record the AoA fluctuations and their PDFs over the entrance pupil at the sub-aperture locations for both types of turbulence. The observations are made in two perpendicular directions to the propagation of the laser beam. The experimental PDFs of the AoA fluctuations are fitted with Gaussian, Lognormal, Weibull, and Gamma distribution functions. The results show that the Weibull and Gamma models are more consistent with the experimental data for the indoor convective air and atmospheric turbulence respectively. For the indoor convective turbulence, the full width at half maximum and the peak location of the measured PDFs increase with the heater temperature, as well as the goodness of fit, which saturates at high temperatures.

Prediction of effective size of a propagated laser beam with a known phase profile and its experimental validation

In this paper we demonstrate that the size of a laser beam, which increases with propagation due to diffraction induced divergence, carrying a given phase profile, can be predicted and the same can be validated experimentally. Since an arbitrary phase profile is also a linear combination of a set of Zernike polynomials hence the divergence corresponding to each Zernike mode can be utilized to estimate the effective size of the beam carrying the arbitrary phase profile. Numerical simulation using the scalar diffraction theory shows how a laser beam with a certain Zernike mode describing its phase profile diverges. Observations from numerical simulations lead to construction of a functional form that can predict the effective size of a laser beam carrying a specific Zernike mode in its phase profile, at different propagation distances. In this paper we develop an experimental arrangement to holographically incorporate a specific phase profile into an incident laser beam. We utilize the programmable control of the beam size for a given propagation distance to achieve different Fresnel numbers. We further develop a detector assembly which can be used to measure the effective size of the beam in the observation plane. We then show experimentally that the effective size of a laser beam propagating distances corresponding to different Fresnel numbers and carrying a known phase profile, described either by a single Zernike mode or a random combination of several Zernike modes, can be very well predicted by the functional form even in a realistic scenario.

Simulation of the dynamics of laser beams in an array of carbon nanotubes using the hydrodynamic approach

We simulated the propagation of a quasi-monochromatic laser beam in a medium with carbon nanotubes. Equations describing the dynamics of laser beams in an array of carbon nanotubes are obtained based on the hydrodynamic approach for the nonlinear Schrödinger equation. This equation is solved numerically using the smoothed particle method. The evolution of the beam is analyzed depending on the frequency of the electric field.

Modeling of hydrocarbon-free potassium flowing-gas diode-pumped amplifier

А 3D CFD model coupled with wave optics model for laser beam propagation is used to calculate the performance of a hydrocarbon-free K end pumped flowing-gas diode pumped alkali amplifier (DPAA). The K DPAA efficiency and output beam quality were calculated as a function of various parameters and the results were compared with those calculated for end pumped Rb DPAA with hydrocarbon-free buffer gas. For moderate pump intensity, both the efficiency and beam quality deteriorate at low gas velocity. The efficiency strongly depends on the pressure of the buffer helium, reaching a maximum at pressure close to atmospheric and falling with a further increase in pressure. The maximum efficiency of the K DPAA (∼0.45) is approximately 4 times higher than that of the Rb one, achieved at the same optimal pump power of 5 kW. Addition of CH4 to the He buffer in the K DPAA decreases the amplifier efficiency and reduces the beam quality.

Measurement of the voltage evolution on a load of X-pinch plasma system using the Pockels effect

A diagnostic system using the Pockels effect (linear electro-optic effect) has been developed to measure a voltage on a load of the SNU X-pinch device [Ryu et al., Rev. Sci. Instrum. 92, 053533 (2021)]. The sensor component of the diagnostic system comprises of a lithium niobate (LN) crystal and its mount. When the LN crystal is subjected to an external electric field, the refractive indices of the LN crystal change due to the Pockels effect, leading to a change in the polarization state of the propagating laser beam through the crystal. This concept allows the separation and shielding of electronic devices from the intense electric pulses generated by the X-pinch system. Furthermore, the compact size and high electric field tolerance of the LN crystal enable us to position the sensor in a close proximity to the load of the X-pinch, facilitating the measurement of voltage evolution on the load. In contrast to circuit-based voltage probes, our sensor possesses low inductance, allowing us to measure resistive-dominant voltage even in the presence of rapid current changes within the X-pinch system. In this paper, we outline the configuration of our voltage measurement system using the LN crystal within the X-pinch device and provide measurement results of the load voltage. Additionally, we explore the temporal evolution of the voltage in relation to the phase transition of the load.

High-Power, High-Purity HG0n Hermite–Gaussian Laser Beam Generation in Cascaded Large Aspect Ratio Slabs

High-power, high-purity, nanosecond (ns) one-dimensional HG0n laser beams are proposed and demonstrated by using Nd:YAG cascaded slabs with a large aspect ratio. The HG0n laser beams are generated by adjusting the pump distribution, the intracavity apertures, and the tilt angle of the output coupler (OC). By controlling the gain and loss of HG0n modes of different orders, the high-purity, one-dimensional, high-order HG0n laser beams with orders 1 to 9 (HG01 to HG09) are produced, and their beam quality factors M2 align well with the theoretical predictions. Meanwhile, the large aspect ratio slab provides an ideal amplifier for the strip-shaped HG0n laser beams, and further power scaling is achieved by seeding the generated HG0n laser beams into an amplifier with an identical slab module. For the HG09 mode, the average power is amplified from 289 mW to 4.73 W with 294 ns pulse width, corresponding to a peak power of 32 kW. Moreover, above 5 W average power is achieved for all HG01 to HG08 modes. Hopefully, this scheme provides a solution for high-power and high-purity HG0n laser beam generation based on the slab-shaped configuration.

Optical Setup for Investigating the Hyperpolarizability of Organic Nanostructure Materials in Solutions Using Electric Field Induced Second Harmonic Generation

Abstract: In this paper, an optical setup for electric field-induced second-harmonic generation (EFISH) at 1.9 μm experiment was arranged and used to investigate and determine the hyperpolarizability of some nanostructure organic components in two different solutions. First, a laser beam at 1.9 μm was generated by pumping a hydrogen Raman cell pressurized to 55 bar with 10 Hz Q-switched Nd: YAG nanosecond laser operating at λ = 1.064 μm. Next, the generated laser beam was aligned with all optical components within the assembly. The final step was to optimize the beam’s power and polarization at the center of the EFSH cell. Different nanostructure organic samples in solutions were prepared with nearly the same standard concentration of about 5 mmol/L to be investigated under the optimized system. Two solvents were used in this work, dichloromethane, or DCM (CH2Cl2), and chloroform, or trichloromethane (CHCl3). First, the harmonic order hyperpolarizability of five organic molecules in solutions with different chemical components such as quinolinium groups and organic boron complexes (supplied by the Chemistry Department at Catania University, Italy) were experimentally investigated experimentally. Only component (2-(2-[5′-(N,N-dimethylamino)-(2,2′-bithiophen)-5-yl]vinyl)-1-methyquinolin-1-ium iodide) in chloroform showed a significant difference in Maker fringes amplitude of the applied electrical field in comparison with fringes of its pure solvent. The value ofμfor this component has been calculated as 1320 x 10-48 esu. This value indicates that the component is a suitable candidate for use in second-harmonic generation imaging for biological applications. Keywords: Electric field-induced second-harmonic generation (EFISH), Harmonic light, Organic materials, hyperpolarizability. PACS: Nonlinear optics, 42.65.-k, Electric fields, instrumentation for measurement, 07.50.-e, Organic-inorganic hybrid nanostructures, 81.07.Pr, Organic materials optical materials, 42.70.Jk

REMOTE MEASUREMENTS OF WATER SURFACE POLLUTION BY THE METHOD OF LASER LOCATION

As it was shown in the nature investigations,the most area of water in the Azerbaijan shore of Caspian Sea is covered by oil film, the square of which depends on direction of wind. The research of pollution's of environment by the mean of optical apparatus of remote sounding, mounted on the board of flying apparatus or space satellites is one of intensely developing directions. The theory of measuring of oil film's thickens by the help of laser location in detail described. The principles of straight¬-line spreading of electromagnetic waves, reflecting of electromagnetic energy by objects and constant speed of their propagation are laid in the basic of location. We have developed lidar for controlling of pollutions of water surface, where helium-neon laser “LGI-102” having power 3mW working in the pulse regime is used as beam radiator. During the experiment the laser was mounted on the plain ground on the distance 1-meter from water surface. The prism was placed in the road of propagation of laser beam and used for direction of radiation under the angle 45 on water surface. Integral photo transducer on the base of local mono-and polycrystalline silicon films with linear output was used in the photo detector device. Photo transducer was made in hybrid form on the base of two crystals: photo sensitive poly-silicon film and unpack operational amplifier 740UD4. Keywords: Pollution, water surface, oil film, laser location, lidar, photo detector.