Divergence Angle Of Laser Beam Research Articles

Calibration method for high-power and wide-band laser beam divergence angle

在大功率激光系统的评价与分析中，激光器的光束品质是系统光束品质的决定性因素，也是激光器验收、鉴定的重要指标，其中束散角是判别激光光束质量的重要参数。本系统测试激光波长的范围比较宽，一般在0.532 μm~10.6 μm之间，没有合适的探测器能够覆盖整个波段，所以采用了一种新的方法来解决宽波段束散角的测量问题。选用CCD成像和扫描狭缝相结合的方法来实现宽波段激光光束束散角的测量，可见光和近红外波段（0.532 μm~1.2 μm）激光光束采用CCD法测量激光束散角，中红外波段（1.2 μm~10.6 μm）激光光束采用扫描狭缝法测量激光束散角。两种方法的结合可以较为精确地测量出不同波段的激光束散角。

Analysis of optimal detection range performance of LiDAR systems applying coaxial optics

In this study, the optimal detection range performance of a LiDAR system employing coaxial optics is analyzed. On analyzing laser beam diameter, beam divergence angle, light-receiving area, and receiving light intensity, the optimal detection range was exhibited when the collimator focal length was 6.5 mm, the laser-beam divergence angle was 1.23 mrad, and the hole of the receiving mirror was 1.4 mm. Furthermore, the maximum deviation of the optical scan angles with respect to the mechanical angles of the polygon mirror and the MEMS mirror were analyzed as -0.99° and +4.54° in the x-axis and y-axis directions, respectively.

Range Difference Between Shallow and Deep Channels of Airborne Bathymetry LiDAR With Segmented Field-of-View Receivers

Significant range differences were identified between shallow and deep channels of Mapper5000 bathymetry LiDAR system with segmented field-of-view (FOV) receivers. Range difference varied with depth and water optical properties. The main feature was the maximum value in range difference curves, which ranged from 0.3 to 0.6 m and usually exceeded the International Hydrographic Organization (IHO) accuracy standards. Sensitivity analyses based on a semi-analytical Monte Carlo simulation model revealed that the scattering phase function and laser beam divergence angle played more important roles in causing pulse dispersion and determining the amplitude and position of maximum range difference than absorption and scattering coefficients. A range difference correction method by fitting existing shallow and deep channel data in the overlapping range with a cubic polynomial was proposed to correct the deep channel data in the entire depth range that LiDAR can detect. Depth discontinuity at the junction of shallow channel and deep channel measurements was successfully removed, and the mean and standard deviation of corrected range difference were within 0.01 m and 0.1 m, respectively. Combination of range difference correction and mean bias corrector can be an alternative method for depth bias correction of segmented-FOV LiDAR when referenced sonar data is not available.

Theoretical and experimental research on crosstalk in spectral beam combining of a laser diode bar with a high fill factor.

Spectral beam combining is an important way to improve the brightness of semiconductor laser beams. For a spectral beam combining system, crosstalk between different emitters would cause the deterioration of beam quality and the reduction of beam combining efficiency, especially for the laser diode bar with a high fill factor. In this paper, an analysis model of the spectral beam combining system with crosstalk is established. The most important advantage of this model is that it can analyze the spectral distribution of the combined beam and also give a relatively good estimation for the beam quality parameters, such as beam size and far-field divergence angle. This model is verified by the experimental results. Furthermore, based on the theoretical model, a method for eliminating crosstalk is developed. By introducing a spatial filter inside the grating external cavity, the crosstalk between different emitters is blocked in the far field, and the beam quality is improved. In the experiment of beam combining of five emitters, after crosstalk is eliminated, the divergence angle of the combined laser beam is reduced from 10.09 to 4.73 mrad, the beam parameter product is reduced from 2.95 to 0.91 mm⋅mrad, and the power of the main lobe is improved from 1.77 to 2 W.

Design and alignment of off‐axis reflection beam expanding and contracting optical system

AbstractThere are special requirements for the laser beam diameter and divergence angle in various optical combination systems, so most of the designs add beam expansion and contraction systems. Off‐axis reflective systems are more widely used in practical applications because of their nonobstructing characteristics and unaffected by chromatic aberration. This paper designs an optical system with both beam expansion and contraction functions by Zemax optical software according to actual needs. The magnification and reduction are 3×. The mirror surface adopts an aspheric design to overcome system aberrations. The off‐axis reflective structure is suitable for lasers of different wavelengths (632.8 nm, 1064 nm, and 1550 nm) without being affected by chromatic aberration. The optical spot diagram shows that the light spot distribution is uniform and meets the magnification and reduction ratio. Besides, combined the dynamic laser interferometer, we install and debug the primary and secondary mirrors of the system and use the laser beam quality analyzer to measure the exit spot of the actual laser beam after passing through the designed optical system. The peak value and root‐mean‐square value of the system transmission wave front are less than 0.1λ. The beam quality test result of the outgoing spot meets the actual application requirements and image quality requirements.

Dynamic measurement of beam divergence angle of different fields of view of scanning lidar* *Project supported by the National Key Scientific Instrument and Equipment Development Projects of China (Grant No. 62027823), the Shenzhen Fundamental Research Program (Grant No. JCYJ2020109150808037), and the National Natural Science Foundation of China (Grant No. 61775048).

The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam. It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance, but also objectively evaluate the performance of the laser system. At present, lidar has received a lot of attention as a core component of environment awareness technology. Micro-electromechanical system (MEMS) micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed. However, due to the small size of the MEMS micromirror, the lidar scanning system has a small field of view (FOV). In order to achieve a wide range of scanning imaging, collimating optical system and wide-angle optical system are generally added to the system. However, due to the inherent properties of the optical lens, it is impossible to perfect the imaging, so the effects of collimating and expanding the beam will be different at different angles. This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.

Laser beam coherence and divergence angle complex controlling technique

To reduce the complexity and cost of partially coherent optical system, increase the convenience of partially coherent laser beam application, in this paper, we presents a method to control the coherence and divergence angle of laser beam complexly, using a liquid crystal spatial light modulator (LC-SLM). First, we introduce the basic theory and method to control the coherence and divergence angle of laser beam complexly using an LC-SLM; then, we put forward the experiment to test the coherence and divergence angle controlling accuracy. The experiment results show that, for a partially coherent laser beam with the coherence and divergence angle of 0.9 mm, 7.5 mrad and 1.5 mm, 3.8 mrad, the error of coherence is less than 5%, the root-mean-square errors of the degree of coherence are 0.027 386 and 0.031 314, and the peak-to-valley values are 0.084 658 and 0.089 103 respectively; the error of divergence angle is less than 5%, the root-mean-square errors of the divergence angle are 0.022 478 and 0.023 186, and the peak-to-valley values are 0.081 201 and 0.092 130 respectively. This method can control degree of coherence and divergence angle with high accuracy.

Characteristics of gain in Ne-like Ar 69.8 nm laser pumped by capillary discharge based on double-pass amplification

In this paper, a double-pass amplification experiment of a Ne-like Ar C line 69.8 nm laser is established. The 45-cmlong capillary is used as the discharge load to obtain a double-pass amplification output of a Ne-like Ar C line 69.8 nm laser. Under the same initial experimental conditions that the initial pressure is 15.4 Pa and the main pulse current amplitude is 13.5 kA, the laser pulse intensity and the full width at half maximum (FWHM) of the laser pulse of the single-pass amplification output and the double-pass amplification output are measured by a vacuum X-ray diode (XRD) behind a vacuum ultraviolet (VUV) monochromator (Acton VSN-515) which is used to disperse the extreme ultraviolet (EUV) emission. And then the laser beam divergence of single-pass amplification output and double-pass amplification output are also measured by a space-resolving flat-field EUV spectrograph combined with an EUV CCD (Andor Newton DO920P-BN). The amplitude of the double-pass amplification laser output is 9 times larger than that of single-pass amplification output, and the FWHM of the double-pass amplification laser pulse is nearly 2.4 ns. While the laser beam divergence angle of the double-pass amplification output is 6.6 times wider than that of single-pass amplification output. By comparing the single-pass amplification and double-pass amplification output experimental results, the gain duration of the gain medium in the double-pass amplification and the radial distribution characteristics of the gain medium are analyzed by using the calculation formula of the double-pass amplification laser intensity. The gain duration is more than 4 ns, during this time the gain coefficient decreases at 1.6 ns. And the gain coefficient is the smallest at 2.8 ns, meanwhile the intensity of the single-pass amplification laser is maximum, and the gain medium is in the gain saturation state. So this result indicates that the minimum gain coefficient at this moment is due to the gain saturation effect. Using a similar calculation method to analyze the spatial distribution of gain coefficients, the gain on the plasma axis is larger than that off the plasma axis. These results lay a foundation for the subsequent establishment of resonant cavity and the multi-pass amplification experiment of capillary discharge Ne-like Ar laser.

Parameters Optimization of Laser-Induced Breakdown Spectroscopy Experimental Setup for the Case with Beam Expander**supported by the 973 Program of China (No. 2012CB921603), National Natural Science Foundation of China (Nos. 61475093, 61127017, 61178009, 61108030, 61378047, 61275213, 61475093, and 61205216), the National Key Technology R&D Program of China (No. 2013BAC14B01), the Shanxi Natural Science Foundation (Nos. 2013021004-1 and 2012021022-1), the Shanxi Scholarship

Improvement of measurement precision and repeatability is one of the issues currently faced by the laser-induced breakdown spectroscopy (LIBS) technique, which is expected to be capable of precise and accurate quantitative analysis. It was found that there was great potential to improve the signal quality and repeatability by reducing the laser beam divergence angle using a suitable beam expander (BE). In the present work, the influences of several experimental parameters for the case with BE are studied in order to optimize the analytical performances: the signal to noise ratio (SNR) and the relative standard deviation (RSD). We demonstrate that by selecting the optimal experimental parameters, the BE-included LIBS setup can give higher SNR and lower RSD values of the line intensity normalized by the whole spectrum area. For validation purposes, support vector machine (SVM) regression combined with principal component analysis (PCA) was used to establish a calibration model to realize the quantitative analysis of the ash content. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The measurement accuracy presented here for ash content analysis is estimated to be 0.31%, while the average relative error is 2.36%.

Pulsed laser induced microbubble in gold nanorod colloid

The characterization of a pulsed laser induced microbubble (PLIMB) in gold nanorod (GNR) colloid was studied experimentally. The generation of PLIMB is due to the optical breakdown in water. Using an ultrasonic transducer and a probing He–Ne laser associated with a photodetector, the photoacoustic (PA) signals and the bubble formation of the multi-cycled oscillation of a single PLIMB were measured simultaneously. Both results are in agreement to show that the lifetime of PLIMB is reduced as the gold concentration increases. This phenomenon is attributed to the plasmonic light scattering (Faraday–Tyndall effect) in GNR colloid; the energy for optical breakdown is reduced at the focus due to laser-beam defocusing. The effect is particularly pronounced at the longitudinal surface plasmon resonance of GNRs. In addition, the divergence angle of 532-nm CW laser beam through gold nanoparticle (GNP) colloid was measured. Our results show that the divergence angle increases as the concentration of GNP increases. This phenomenon again elucidates Faraday–Tyndall effect.

Investigation of single-mode fiber degradation by 405-nm continuous-wave laser light

The degradation of 405-nm fiber-coupled diode laser systems with more than 50 mW power was investigated in detail with focus on the effects occurring at the input end. The coupling and transmission loss of the laser light were associated with the growth of a projection and a periodic structure on the input surface. To avoid this degradation, a short launch fiber with a good surface quality was used at the input end. In this way, the power transmission was stabilized for at least one month. However, structural degradation was noticed on the output surface of the single-mode fiber. To investigate this effect, the damaged samples were measured after different periods of time and examined with a scanning electron microscope and with an atomic force microscope. Reproducible spherical projections with a submicron periodic structure were found in the core region. Additionally, the spectral loss of the fiber was measured, showing the formation of color centers in the deep ultraviolet along the length of the fiber. These investigations were accompanied by simulations of the growth of the structure on the output surface. The influence of the structure was mainly on the divergence angle of the emitted laser beam, reducing the beam quality for applications.

A novel automatic measurement method of laser beam divergence angle based on two linear array charge coupled devices

We propose a scanning imaging measurement method using two linear array charge coupled devices (CCD) to evaluate the transmission performance of the linear laser beam of 90° × 2°. The two linear array CCDs are placed at two positions in the far field separated by a definite angle. The beam divergence angles in the view direction are measured by linear fitting because the beam width conforms to the linear relationship in the far field. This method has the ability for real-time testing and is appropriate for the complicated beam shapes with a wide measurement range.

Effect of Atmospheric Attenuation on Laser Communications for Visible and Infrared Wavelengths

A theoretical study and analysis of the effect of some weather parameters on the laser light source of optical signal in free space (FSO), were discussed. The effect of these parameters on attenuation coefficient of the laser beam was calculation at wavelengths (650, 785 and 1550) nm. The attenuation coefficient was (0.698, 0.546 and 0.225) dB/km for wavelengths (650, 785 and 1550) nm respectively at a visibility of 20 km. We studied as well the receiver optical power, data transfer rate and link margin under the influence of the weather conditions. It was found that weather conditions such as (clear, haze, thin fog, light fog, heavy fog) effect on those wavelength at different ways. It is feasible to enhance the system performance such as link range and data transfer rate by increasing transmitting power and decreasing laser beam divergence angle.

Optimum signal input distribution design in the presence of random pointing jitter for intersatellite optical communications

Channel capacity is widely investigated for free space optical links to approach high-speed data-rate communication. Instead of traditional equiprobable binary symbol input distribution, an optimum input distribution is proposed with respect to channel capacity by maximizing mutual information for intersatellite optical communications in the presence of random pointing jitter. It is shown that the optimum input distribution varies with the variance of pointing jitter σ and laser beam divergence angle w0 and the normalized intensity threshold IT. For traditional normalized intensity threshold IT=0.5, the optimum input distribution ranges from about p(x=0)=0.52 for weak pointing jitter to about p(x=0)=0.24 for strong pointing jitter given the same laser beam divergence angle. The results obtained in this paper will be useful for intersatellite optical communication system design.

Fiber-Optic Vibration Measurement for Low Refractive-Index Media Using Wavefront Splitting Interferometry

A fiber-optic vibration measurement technique based on the wavefront-splitting interferometry is presented in this paper. Due to a small divergence angle of Gaussian laser beam emitting from a single-mode fiber, the sensing beam propagating toward the specimen has an incident angle of nearly 90°, so that the reflection coefficient of specimen surface is relatively high even for low-refractive-index materials. In preliminary tests, overhead-projector transparency was used to demonstrate the vibration measurement with our fiber-optic vibration sensor up to 4 kHz. The Young's modulus of the transparency was also determined by using the vibration method, and the result agreed well with that measured by using a conventional testing machine.

Free-Space Optical communication using visible light

The possibility of visible red light laser being used as signal light source for Free-Space Optical (FSO) communication is proposed. Based on analysis of transmission in atmospheric channel concerning 650 nm laser beam, performance of wireless laser communication link utilizing a low power red laser diode was evaluated. The proposed system can achieve a maximum range of 300 m at data rate 100 Mb/s theoretically. An experimental short-range link at data rate 10 Mb/s covering 300 m has been implemented in our university. It is feasible to enhance the system performance such as link range and data rate by increasing transmitting power and decreasing laser beam divergence angle or through other approaches.

Spectral Characteristics of 50 GHz FSR Etalon for Wide-band DWDM Application

The periodic transmission spectrum of a solid etalon for wide-band capability is analyzed both theoretically and experimentally. In the transmission spectrum with an incident area of a photodetector, the peak wavelength and transmittance are deeply dependent on the incident angle and the divergence angle of the input laser beam. A thermal adjustment for a solid etalon is an optional way to control the transmission spectrum instead of the inefficient fine-angle alignment. In the result, we present the deviations of free spectral range (FSR) by the change in angle and temperature over wide wavelength range.

Application of Geometrical Form Factor in Differential Absorption Lidar Measurement

The peak position for a lidar return signal is calculated and measured for the horizontal path with variation of the laser beam divergence angle (θ), and the inclination angle (δ) between the telescope and laser axes. This work shows that θ and δ are very important parameters to use in the design or alignment of a lidar system receiving a good lidar signal. This paper describes an experimental determination of geometrical form factors in the lidar equation. We receive the signals and determine the geometrical form factors by slope method in a homogeneous atmosphere. The differential absorption lidar equation is evaluated for the dual-pulse lidar system. A method using a geometrical form factor determined by the experiment is introduced to correct the error in C2H4 measurement. This method shows good correction of measurement error in lidar dual-pulse operation, especially in the short range.

Evaluation of laser hazards to the eye and the skin.

Abstract Laser eye and skin hazards are evaluated by comparing direct-exposure intensity levels on the surface of the eye or skin to exposure guidelines equal to (a) threshold effect levels where the skin or cornea is affected and (b) conservatively safe levels based on worst case assumptions where the retina is affected. Equations are presented for calculating the exposure intensity when the laser beam parameters and the range are known. Intensity amplification factors of the eye are indicated for the three cases encountered in practice: (a) where simple geometric optics apply, (b) where the laser beam divergence angle is limiting, and (c) where Fraunhofer diffraction effects are limiting. Diffraction effects predict the maximum eye intensity amplification and hence define the worst case for retinal exposure. The resultant exposure guidelines are summarized, and estimates are made of the associated safety factors. These exposure guidelines quickly identify problem areas that may require more complicated ...