Polarization Characteristics Of Laser Research Articles

Effect of Spontaneous Emission in Hollow Waveguide on Gas Absorbance Measurement by Absorption Spectroscopy

Hollow waveguide (HWG) as an absorption cell for gas spectral sensing has the advantages of low transmission loss, fast response speed, and high path length to volume ratio. However, due to the tubular structure of the HWG, the spontaneous emission generated in the HWG will be transmitted together with the incident laser, which reduces the measured absorbance. We measured and verified the spontaneous emission at the outlet of the HWG by basing on the laser gas absorption spectroscopy and combining with the distinguished polarization characteristics of laser and spontaneous emission. Then, we quantitatively determined the intensity distribution of the spontaneous emission output from the HWG based on the infrared (IR) imaging using an IR camera. We also investigated the effect of the spontaneous emission on the measured absorbance as a function of the HWG length by comparative experiments. The effect exponentially decreases as the HWG length increases since the increased loss. The method could be used for designing or optimizing of HWG-based sensors.

The Research of Long-Optical-Path Visible Laser Polarization Characteristics in Smoke Environment

The concentration of smoke in an environment can cause obvious interference to visible light intensity imaging, and it is a non-negligible factor in the polarized imaging of ground-based targets. Smoke particles cause severe scattering of photon intensity, resulting in polarization. In this case, low-visibility targets can be effectively identified by detecting the polarization dimension of targets. However, the polarization transmission of smoke in an environment is unclear, and the theoretical simulation lacks experimental reliability verification. To study this problem, this study constructs a polarization transmission model in a smoke environment and simulates and analyzes the scattering of visible polarized light at 450, 532, and 671 nm under different smoke densities. The optical thickness is determined to establish a reliable connection between the simulation and the external field long optical path test and verify the transmission of polarized light. Results show that the method has a 60% confidence in the polarization transmission model. With the increase in optical thickness, the degree of polarization (DOP) of the three wavelengths in the visible light band decreases, and the DOP of each polarized light decreases. No obvious difference is found between the DOPs of circularly polarized light at 450 nm and linearly polarized light. The DOP of circularly polarized light at 532 nm is 1–5% higher than that of linearly polarized light, 1–10% higher than that of the outdoor test, 1–5% higher than that of circularly polarized light at 671 nm, and 2–15% higher than that of the outdoor test. Therefore, the shorter the wavelength in the visible band, the higher the DOP. With the increase in wavelength, the polarization characteristics of circularly polarized light are gradually better than those of linearly polarized light.

非球型粒子对激光偏振特性的影响

非球型粒子对激光偏振特性的影响

不同湿度环境下可见光波段激光偏振特性研究

不同湿度环境下可见光波段激光偏振特性研究

Effect of underwater suspended particles on the transmission characteristics of polarized lasers

The complex problem related to the transmission channel of underwater polarized lasers is caused by underwater suspended particles. In order to study the effect of suspended particles on underwater optical communication links and laser polarization characteristics, a method based on a combination of Mie scattering theory and Monte Carlo numerical simulation is used to establish the transmission model of underwater photons. This method is applied to analyze the effect of suspended particles on normalized received energy and channel delay. We also investigate the effects of particle and channel length on the polarization characteristics of four different types of polarized lasers. Theoretical analysis and simulation results indicate that the optical coefficients of particles increase with increasing particle size. Thus, when the transmission channel length is the same, the received normalized energy and light intensity will decrease, and the channel time delay will increase. Meanwhile, a depolarization phenomenon with respect to the laser will be generated with increasing particle size, and particle size has a greater effect on linearly polarized light than circularly polarized light. Therefore, circularly polarized light maintains good polarization characteristics in the underwater laser transmission process.

Output characteristics of Nd:GdVO4 crystals laser with dual c-axis orthogonal gains end-pumped by two fiber-coupled diode lasers

The output characteristics of neodymium-doped gadolinium vanadate (Nd:GdVO4) crystals laser with dual c-axis orthogonal gains end-pumped by two fiber-coupled diode lasers are investigated. With two 1 W semiconductor diode lasers pumping, the output power of TEM00 laser is 920 mW, and the optical conversion efficiency is close to 46%. By changing the relative orientations of both Nd:GdVO4 crystals, the polarization characteristics of laser are varied. In particular, by keeping the c-axes of two Nd:GdVO4 crystals orthogonal to each other and adjusting two diode pump lasers to operate at the same power level, the completely unpolarized light is obtained.

Short-Range Detection System with Polarized Laser and Polarization Characteristics of Typical Targets

In view of using only the intensity information of retroreflection light and poor capacity of anti-interference in laser short-range detection, this paper presents a short-range detection method based on laser polarization properties of targets, designs the polarization detection model and constructs the polarization detection system. Through the analysis and the comparison of data which is obtained from the polarization characteristic and intensity characteristic experiments of five different targets, the conclusion that the detection method based on the laser polarization characteristics can effectively distinguish target is achieved. Meanwhile, the analysis of detection model in this paper can also provide certain theory significance for further research on polarization detection.

Polarization characteristics of He–Ne laser with different directions of polarized feedback

A polarizer is placed in an external feedback cavity to form polarized optical feedback. The effect of the different directions of polarized optical feedback on laser polarization characteristics (LPCs) is investigated experimentally and theoretically. The angle between the optical axis of the polarizer and the laser polarization is changed from 0° to 90°. It is found that LPCs vary greatly under different directions of polarized optical feedback. The angle range can be divided into five zones (two flipping zones, ⊥-polarization zone, bistable zone, and ∥-polarization zone) according to the different LPCs. When the angle is in the range of the ⊥-polarization zone (∥-polarization zone), the laser outputs ⊥-polarization (∥-polarization). Thus, one can choose either ⊥-polarization or ∥-polarization by properly aligning the axis of the polarizer.

Analysis and Simulation of Laser Polarization Characteristics on Metal Surface in Short-Range Detection

In view of using only the intensity information of retroreflection wave and poor capacity of anti-interference in laser short-range detection, this paper analyzes the polarization characteristics of laser beam on the metal surface and establishes reflection model of polarized laser. A target detection method based on polarization characteristics of reflection laser is putted forward and the simulation of polarization characteristics on the surface of several typical metal targets is implemented at last.

Photon-spin controlled lasing oscillation in surface-emitting lasers

We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time.

Induced dichroism in passive laser switches

The characteristics of absorption saturation in resonant polarization-inhomogeneous media of passive laser switches (made of LiF crystals with color centers and of a solution of 1052 dye) were investigated theoretically and experimentally. The induced dichroism was determined: in the case of the dye switch it agreed with the theoretical predictions, whereas in the case of the lithium fluoride switch it was slightly less than the calculated value because of depolarization of the bleaching wave in the crystal as a result of residual birefringence. It was concluded that allowance for the induced dichroism was essential in studies and interpretation of the polarization characteristics of lasers with passive Q switching.

Multiphoton ionization and two-photon fluorescence excitation spectroscopy of triethylenediamine

The multiphoton ionization (MPI) and two-photon fluorescence excitation (TPFE) spectra of triethylenediamine (DABCO) are obtained and analyzed. A low-lying state (0–0 at 35 795 cm−1) is observed as a two-photon resonance in the four photon ionization spectrum and also in the TPFE spectrum. Circular vs linear laser polarization studies give an A′1 symmetry for this state. The state results from a 3s (+) ←n (+) orbital promotion. The vibrational progressions and sequences observed are also analyzed. The lifetime of the fluorescence resulting from two-photon 1A′1←1A′1 excitation compares well with the lifetime observed upon one-photon ?←? excitation,suggesting that the 1A′1 state is the emitting state. This 1A′1← 1A′1 one photon forbidden, two-photon allowed, transition is most probably responsible for the very weak long wavelength absorption reported in previous conventional spectroscopic studies. The MPI spectra and laser polarization characteristics of the strong (0–0 at 39 825 cm−1) transition of DABCO are also investigated. The transition is found to be both one- and two-photon allowed and is assigned as 1E″[3px,y (+)]←1A1[n (+)].

Energy and polarization characteristics of a neodymiumglass laser with plane-parallel and telescopic resonators

A study was made of the influence of the birefringence of the active medium on the energy and polarization characteristics of a laser with an intraresonator polarizer. The relevant quantities were calculated on a computer. It was found that a slight birefringence had less influence on the polarization characteristics of the laser radiation when a telescopic resonator was used.

Calculation of polarization characteristics of lasers

Calculation of polarization characteristics of lasers