Laser Transmission Characteristics Research Articles

Aero-optical effects of a hypersonic vehicle based on the refractive index step ray tracing method

The aero-optical effect caused by the high-speed flight of aircraft can affect the accuracy of astronomical navigation, so studying the laser transmission characteristics in high-speed flow fields is essential. This study adopts a 3D spherical blunt cone model as the physical aircraft model, incorporates the latest reanalysis data from the National Centers for Environmental Prediction as atmospheric parameters, and uses Fluent software to establish a hypersonic aircraft external flow field model. The ray tracing error is calculated using a method based on the refractive index step size. Results indicate that, under the conditions of flying altitude of 5 km and incident angle of 45°, the proposed ray tracing method has better accuracy than the traditional method. Compared with the Runge–Kutta method and the method based on geometric step size, the proposed ray tracing method reduces the error by 46.4% and 12.5%, respectively, at the flight Mach number of 5.

Polarization Transmission Characteristics of Blue-Green Laser in Cross-Medium Downlink

Polarization Transmission Characteristics of Blue-Green Laser in Cross-Medium Downlink

Backscattering Echo Intensity Characteristics of Laser in Soil Explosion Dust

Soil dust generated by explosions can lead to the absorption and scattering of lasers, resulting in low detection and recognition accuracy for laser-based devices. Field tests to assess laser transmission characteristics in soil explosion dust are dangerous and involve uncontrollable environmental conditions. Instead, we propose using high-speed cameras and an indoor explosion chamber to assess the backscattering echo intensity characteristics of lasers in dust generated by small-scale explosive blasts in soil. We analyzed the influence of the mass of the explosive, depth of burial, and soil moisture content on crater features and temporal and spatial distributions of soil explosion dust. We also measured the backscattering echo intensity of a 905 nm laser at different heights. The results showed that the concentration of soil explosion dust was highest in the first 500 ms. The minimum normalized peak echo voltage ranged from 0.318 to 0.658. The backscattering echo intensity of the laser was found to be strongly correlated with the mean gray value of the monochrome image of soil explosion dust. This study provides experimental data and a theoretical basis for the accurate detection and recognition of lasers in soil explosion dust environments.

Laser transmission and attenuation characteristics in high-speed flow field

Laser transmission and attenuation characteristics in high-speed flow field

Analysis of Transmission Depth and Photon Number in Monte Carlo Simulation for Underwater Laser Transmission

The modeling of laser transmission characteristics in complex seawater is fundamental for bathymetric and oceanographic laser detection systems. Because the factors affecting laser transmission in seawater are independent of one another, firstly, in this paper, a Monte Carlo model of laser propagation in seawaters with suspended matter was established to study the influence of suspended matter with specific radius on the underwater laser transmission. Secondly, the influence of transmission depth and the number of photons on the laser extinction coefficients of seawater containing different concentrations of suspended matter were analyzed, respectively. Thirdly, the relationships between maximum transmission depth, the number of initial photons, and the concentrations were built and verified by simulations. Lastly, an experimental platform was set up and experiments were carried out to verify the Monte Carlo model and the relationships. Results show that (1) both the minimum initial photon number and maximum transmission depth depend exponentially on the concentrations of the suspended matter; (2) the extinction coefficients obtained by the Monte Carlo model and those obtained by experiments are consistent. The absolute values of the differences are less than 0.028 m−1, implying that (1) the proposed Monte Carlo model is effective for simulating laser propagation in seawaters with suspended matter; (2) the established relationships between maximum transmission depth, the minimum initial photon number, and the concentrations of suspended matter have better accuracies, which are valuable for the simulations on attenuation of laser transmission in seawater. The method of this paper can also be extended to the study of suspended solids with other radii and improve the simulation accuracy and decrease simulation time consumption.

Phase Function of Seawater Polluted by Oil Emulsion

Oil droplets suspended in the seawater will seriously affect the transmission characteristics of electromagnetic wave from ultraviolet and visible light to infrared. The scattering phase function can show the laser transmission characteristics in seawater polluted by oil. Water with oil emulsion has a phase function significantly different from that of natural ocean water. The accurate calculation of phase function can lay the foundation for laser propagation in the oil spill seawater, and is of great significance for protection of marine environment. This paper presents the modeling of phase function of seawater polluted by dispersed oil based on Mie scattering theory. Numerical calculation of scattering phase function of dispersed oil droplets in various times and at different wavelengths is conducted, and the numerical results of Henyey-Greenstein phase function and the modified Henyey-Greenstein phase function is given. The results show that the shapes of Mie scattering phase function of water with oil emulsion depend on wavelength and the oil emulsion ageing. The forward scattering attenuates with the time of oil emulsion ageing and the increase of incident wavelength, and the scattering gradually becomes homogeneously. Compared with Henyey-Greenstein the modified Henyey-Greenstein phase function can describe the scattering property of oil emulsion in the seawater better. But the fitting effects of both Henyey-Greenstein phase function and the modified Henyey-Greenstein phase function are undesirable for long time oil droplets, long wavelength and strong absorption ultraviolet light.

Transmission Characteristics of Blue-green Laser Through Two-Dimensional Dynamic Sea Surface-Bubble Layer

Transmission Characteristics of Blue-green Laser Through Two-Dimensional Dynamic Sea Surface-Bubble Layer

Methane near-infrared laser remote detection under non-cooperative target condition based on harmonic waveform recognition

A 2f/1f signal processing technique with harmonic waveform recognition method is proposed. The proposed method is used in the methane near-infrared laser remote detection system to solve the instability problems caused by the amplitude fluctuation and the deformation of the harmonic signal during the methane remote sensing under non-cooperative target conditions. The methane remote sensor system based on near-infrared tunable diode laser absorption spectroscopy (TDLAS) and improved WMS-2f/1f method is developed. The laser transmission characteristics under non-cooperative target conditions were analyzed using Monte Carlo ray tracing method. The linear relationship (R2 = 0.9969) fitted by experimental data between the amplitude of 2f/1f signal and methane concentration. The stability test and Allan deviation analysis of methane TDLAS telemetry sensor is conducted. The results illustrate that a minimum detection limit (MDL) of 2.66 ppm·m for the improved WMS-2f/1f method is obtained with the averaging time of 273.8 s. The MDL is significantly lower than the conventional WMS-2f/1f method. The experimental results verify that the improved WMS-2f/1f method is adopted to reduce the signal fluctuation influence and improve the detection stability.

Analysis of temporal and spatial distribution characteristics of ammonium chloride smoke particles in confined spaces

In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes, this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investigates an experimental laboratory smoke environment using an ammonium chloride smoke agent. The particle size distribution, composition, and mass flow distribution of the smoke were studied. Based on a discrete phase model and a k-ε turbulence model, a numerical simulation was developed to model the smoke generation and diffusion processes of the smoke agent in a confined space. The temporal and spatial distribution characteristics of the smoke mass concentration, velocity, and temperature in the space after smoke generation were analyzed, and the motion law governing the smoke diffusion throughout the entire space was summarized. Combined with the experimental verification of the smoke environment laboratory, the results showed that the smoke plume changed from fan-shaped to umbrella-shaped during smoke generation, and then continued to spread around. Meanwhile, the mass concentration of smoke in the space decreased from the middle outward; the changes in temperature and velocity were small and stable. In the diffusion stage (after 900 s), the mass concentration of smoke above 0.8 m was relatively uniform across an area of smoke that was 12 m thick. The concentration decreased over time, following a consistent decreasing trend, and the attenuation was negligible in a very short time. Therefore, this system was suitable for conducting experimental research on laser fuzes in a smoke environment. Owing to the stability of the equipment and facilities, the setup could reproduce the same experimental smoke environment by artificially controlling the smoke emission of the smoke agent. Overall, this work provides a theoretical reference for subsequent research efforts regarding the construction of uniform smoke environments and evaluating laser transmission characteristics in smoky environments.

All-Fiber Gas Cavity Based on Anti-Resonant Hollow-Core Fibers Fabricated by Splicing with End Caps

In recent years, fiber gas lasers have obtained a rapid development, however, efficient and stable pump coupling is a key limitation for their applications in the future. Here, we report an all-fiber gas cavity based on anti-resonant hollow-core fibers which have the beneficial properties of adjustable broad transmission bands and potential low transmission attenuation, especially in the mid-infrared. This kind of all-fiber gas cavity is fabricated by directly splicing with end caps at both ends for the first time. The high-power laser transmission characteristics were studied, and the experimental results show that the all-fiber gas cavities have a very stable performance. The maximum input laser power at 1080 nm is about 260 W, and the output power is 203 W, giving a total transmission efficiency of 78.1%. This work opens a new opportunity for the development of high-power all-fiber structured fiber gas lasers.

A Fast Analysis Method for Blue-Green Laser Transmission through the Sea Surface.

The fast estimation of blue-green laser transmission characteristics through the fluctuating sea surface, such as refraction angles and transmittance, is very important to correct operating parameters, detection depth and anti-detection warning in airborne Light Detection and Ranging (LiDAR) applications. However, the geometry of the sea surface is changed by complex environment factors, such as wind and wave, which significantly affect the rapid acquisition of the blue-green laser transmission characteristics. To address this problem, a fast analysis method is provided to rapidly compute the blue-green laser transmittance and refraction angles through the fluctuating sea surface driven by different wind directions and speeds. In the method, a three-dimensional wave model driven by the wind was built to describe the wave spatial distribution varying with time. Using the wave model, the propagation path of the scanning laser footprint was analyzed using the proposed meshing method, thus the transmittance and refraction angles of the optical path can be fast obtained by using parallel computing. The simulation results imply that the proposed method can reduce the time consumption by 70% compared with the traditional analytical method with sequential computing. This paper provides some statistical laws of refraction angles and transmittance through the fluctuating sea surface under different wind conditions, which may serve as a basic for fast computation of airborne LiDAR transmission characteristics in complex environments.

Influence Characteristics of Laser Transmission Amplitude Fluctuation Based on Turbulent Medium

In order to study the transmission characteristics of laser in atmospheric turbulent medium and understand the influence degree of various factors on amplitude fluctuation, by means of smooth perturbation method, this paper establishes a theory model of amplitude fluctuation of laser propagation in turbulent medium by using the smooth perturbation method and reflects the amplitude fluctuation degree, carries out specific discussion on each influence factor. The results show that the larger the wavelength, the more stable the amplitude fluctuation. With the increase of laser section radius, the amplitude fluctuates sharply and then decreases slowly after reaching the peak. Transmission distance is the main influence factor of amplitude fluctuation. With the increase of transmission distance, the amplitude fluctuation will become more obvious. The amplitude acquisition can be comprehensively modulated in a specific transmission distance by wavelength and section ra-dius, so as to ensure the stability of the received laser and provide a theoretical basis for the interferometry technology.

Fluctuation characteristics of laser transmissions in atmospheric turbulence

In order to study the transmission characteristics of lasers in turbulent atmospheric media, and to discuss the fluctuations of laser beams that are caused by various factors, and thereby effectively and clearly detect target objects, this study uses the far field approximation method of physical optics in combination with statistical optical theory to study the vertical and horizontal fluctuations of lasers in atmospheric turbulence, and establish a corresponding transmission fluctuation model. A statistical fluctuation model of lasers is established after considering the combined effect of various influencing factors. Our research shows that the main factors affecting the horizontal fluctuation function are the spatial correlation coordinates, and are unrelated to vertical. The vertical fluctuation function is affected by both the spatial correlation function and vertical distance. In the statistical fluctuation function, the vertical distance of the observation point is the main factor affecting laser transmission. Our research provides a theoretical foundation for turbulence analysis and laser echo detection.

Phase characteristic and information transmission of laser signals through plasma in shock tube

Laser communication is a promising way of achieving effective communication during reentry. This paper focuses on the phase characteristics and information transmission of laser signals in plasma sheaths. First, propagation of the laser signals through the sheaths is analyzed theoretically. Next, phase characteristics of the periodic laser signals are studied by ground simulation experiments in shock tube. Further, experiments of the pseudorandom amplitude and phase modulated signals are conducted. Finally, information transmission is tested. This paper is the basic research of laser transmission characteristics in plasma sheaths and has experimentally realized successful information transmission in the plasma generated by shock tube. The results could provide reference for the future ground and flight experiments.

Simulation of Laser Transmission Characteristics under Aerosol Conditions Based on Monte Carlo Method

Simulation of Laser Transmission Characteristics under Aerosol Conditions Based on Monte Carlo Method

Research on the propagation characteristics of blue-green laser through sea surface with foams

Submarine laser communication is a kind of technology which uses blue-green laser to carry on the data transmission between the aircraft or ship and deep water. The laser transmission characteristics are greatly influenced by the air/sea interface, which becomes rougher and even covered with foams because of wind speed as well as other acting force. In this paper, by using the Kirchhoff approximation, the influences of polarization state and the incident wave on the transmission characteristics were studied, based on the Mie theory and the radiative transfer theory, the transmission characteristics of blue-green laser through rough sea surface with foams were analyzed in detail, the influences of the roughness of sea surface and wind speed on laser transmission and energy distribution were analyzed. The results show that the energy distribution of blue-green laser through sea surface is more concentrated compared to microwave, which mainly distributed in the refraction direction, the transmission characteristics have a great dependence on the roughness and wind speed. This provides a certain theoretical basis for related research.

Dispersion of near-infrared laser energy through radicular dentine when using plain or conical tips.

The aim of this study was to investigate the influence of tip design on patterns of laser energy dispersion through the dentine of tooth roots when using near-infrared diode lasers. Diode laser emissions of 810 or 940nm were used in combination with optical fiber tips with either conventional plain ends or conical ends, to irradiate tooth roots of oval or round cross-sectional shapes. The lasers were operated in continuous wave mode at 0.5W for 5s with the distal end of the fiber tip placed in the apical or coronal third of the root canal at preset positions. Laser light exiting through the roots and apical foramen was imaged, and the extent of lateral spread calculated. There was a significant difference in infrared light exiting the root canal apex between plain and conical fiber tips for both laser wavelengths, with more forward transmission of laser energy through the apex for plain tips. For both laser wavelengths, there were no significant differences in emission patterns when the variable of canal shape was used and all other variables were kept the same (plain vs conical tip, tip position). To ensure optimal treatment effect and to prevent the risks of inadvertent laser effects on the adjacent periapical tissues, it is important to have a good understanding of laser transmission characteristics of the root canal and root dentine. Importantly, it is also essential to understand transmission characteristics of plain and conical fibers tips.

光学镜面洁净度对激光传输特性的影响

光学镜面洁净度对激光传输特性的影响

FPGA Implementation for CCD Driving and Laser Spot Position Detection

CCD sensor can be used as the imaging device in the initial aiming processing for the beacon laser, and can also be used as the detecting device for the communication lasers optical axis alignment error of the targeting captured trace (APT) unit in space laser communication system. In this paper, based on a double-FPGA structure, we proposed technical solutions to realize the imaging CCD sensor driving and the laser spot position detection algorithm for the CX285AL image sensor by using the overall design of the system block diagram. The spot position detection wave door track centroid algorithm for CCD sensor is also studied by using the analysis of laser transmission characteristics of the atmospheric turbulence. The simulation analysis and field tests have been verified the feasibility of this approach.

Study on Atmospheric Transmission Characteristics of the Mid-Infrared Laser

A growing number of applications are calling for the compact laser sources operating in the 2~5μm, which is called the mid-infrared spectral region. In general, a laser beam is attenuated, broadened, defocused and may even be deflected as it propagates through the atmosphere. In this paper, the transmission characteristics of mid-infrared laser which covers the whole 2~5μm spectral band are theoretical analyzed, and the computational simulation results are given.