Effect Of Laser Polarization Research Articles

Laser polarization control of ionization-injected electron beams and x-ray radiation in laser wakefield accelerators

In this paper, we have studied the influence of laser polarization on the dynamics of the ionization-injected electron beams, and subsequently, the properties of the emitted betatron radiation in laser wakefield accelerators (LWFAs). While ionizing by strong field laser radiation, the generated photo-electrons carry a residual transverse momentum in excess of the ionization potential via the above threshold ionization (ATI) process. This ATI momentum explicitly depends on the polarization state of the ionizing laser and eventually governs the dynamics of the electron beam trapped inside the wake potential. In order to systematically investigate the effect of the laser polarization, here, we have employed complete three-dimensional particle-in-cell simulations in the nonlinear bubble regime of the LWFAs. We focus, in particular, on the effects the laser polarization has on the ionization injection mechanism, and how these features affect the final beam properties, such as beam charge, energy, energy spread, and transverse emittance. We have also found that as the laser polarization gradually changes from linear to circular, the helicity of the electron trajectory, and hence the angular momentum carried by the beam, increases significantly. Studies have been further extended to reveal the effect of laser polarization on the radiation emitted by the accelerated electrons. The far-field radiation spectra have been calculated for the linear and circular polarization states of the laser. It has been shown that the spatial distributions and the polarization properties (Stokes parameters) of the emitted radiation in the above two cases are substantially different. Therefore, our study provides a facile and efficient alternative to regulate the properties of the accelerated electron beams and x-ray radiation in LWFAs, utilizing ionization injection mechanism.

Fabrication of and characterization of directional antibody-conjugated gold nanourchin colloid and effect of laser polarization on SERS detection of breast cancer biomarker in serum

We describe the results of citrate-stabilized 100 nm gold nanourchins (GNU) functionalized and conjugated with monoclonal antibody (mAb) in directional orientation to investigate the interaction with breast cancer serum (BCS) overexpressed with CA 15–3 biomarker. UV-Vis, fluorescence, FT-NIR spectroscopy, and SERS with 637 nm Raman probe were employed for non-destructive analysis. UV-Vis spectroscopy exhibited two distinct peaks at 230 and 280 nm related to tyrosine (Tyr) and tryptophan (Trp) with the corresponding fluorescence peaks at 285 and 315 nm respectively. FT-NIR showed some new lines after the interaction such as CH2 combination in carbohydrates, and NH2 amino acids. Directional orientation indicated a higher SERS intensity than random due to higher parallel dipole moments of asymmetric molecules and the polarization sensitivity of GNU. The SERS signals increased significantly after the interaction and the intensity of the Raman lines varied nonlinearly with the laser power. The data were filtered using the filtfilt filter from scipy.signals, baseline corrected using the Improved Asymmetric Least Squares (isals) function from the pybaselines.Whittaker library, and normalized using the minmax_scale function from sklearn.preprocessing. The scikit-learn Principal Component Analysis (PCA) function was used to analyze the dataset by identifying the directions of maximum variability in the data.

Effect of laser polarization on atomic and ionic emissions in Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-Induced Breakdown Spectroscopy (LIBS) is attracting a great deal of interest in qualitative and quantitative analysis of materials. Close observation reveals that developments in the science that underpins LIBS as an analytical technique are limited to either signal enhancement strategies or newer data analysis techniques that facilitate better interpretation of raw LIBS data. Developments related to the excitation part of LIBS have been restricted to the effects of laser beam characteristics or the effect of ambient experimental conditions. The influence, if any, of the polarization state of the excitation laser has largely remained unexplored. We address this lacuna by probing the influence of different polarization states of the excitation laser on LIBS spectra of metals (copper and silver) and non-metals (polyethylene) by analyzing the polarization-dependent behavior of both atomic and ionic emission lines. Our observations open the possibility of tackling the problem of relatively faint emissions from ionic species in the plasma by appropriately manipulating the polarization state of the incident laser beam; this may lead to easy-to-implement improvement in the performance of LIBS instruments.Graphical abstract

Generation of isolated and polarized γ-ray pulse by few-cycle laser irradiating a nanofoil

An isolated ultra-short γ-ray pulse is a unique tool for measuring ultrafast-physics processes, such as imaging intra-nuclear dynamics and inner-shell electron dynamics. Here, we propose an all-optical efficient scheme for generating isolated ultra-short γ-ray pulse from a laser-driven nanofoil. When a few-cycle circularly polarized laser pulse with an intensity of 1022 W cm−2 irradiates a nanofoil, the electrons in the nanofoil are pushed forwards collectively, forming a single relativistic electron sheet (RES) with a charge of nC. The electrons are substantially accelerated to high energies by the super-ponderomotive force of the laser. Then, a counter-propagating laser pulse with a peak intensity of 1021 W cm−2 collides with the RES, resulting in the generation of an isolated sub-femtosecond γ-ray pulse via nonlinear Compton scattering. The effect of laser polarization on the polarization degree of γ-rays is investigated by using a proof-of-principle calculation. It is shown that a highly polarized isolated γ-ray pulse with a cut-off energy of 100 MeV can eventually be generated in a head-on collision configuration when the scattering laser is linearly polarized. Such an isolated ultra-short polarized γ-ray source would provide critical applications in high-energy physics, laboratory astrophysics and nuclear physics.

Ultrafast time-resolved single-shot birefringence microscopy for laser-induced anisotropy.

The interaction between ultrashort laser pulses and materials in the ultrafast time domain, especially regarding the effect of laser polarization, has attracted much attention. In this study, ultrafast time-resolved single-shot birefringence microscopy is performed to observe laser-induced anisotropy. The birefringences of the optical Kerr effect and laser-induced anisotropic nanostructures by femtosecond laser pulses in silica glass are measured, and their slow axis is confirmed to correspond to the linear polarization angle of the pump light. We discuss the time variations of these birefringences in the picosecond time domain.

Femtosecond laser-induced Cu plasma spectra at different laser polarizations and sample temperatures

Laser-induced breakdown spectroscopy (LIBS) is a good technique for detecting and analyzing material elements due to the plasma emission produced by the high-power laser pulse. Currently, a significant topic of LIBS research is improving the emission intensity of LIBS. This study investigated the effect of laser-polarization on femtosecond laser-ablated Cu plasma spectra at different sample temperatures. The measured lines under circularly polarized lasers were higher than those under linearly and elliptically polarized lasers. The enhancement effect was evident at higher Cu temperatures when comparing the plasma spectra that have circular and linear polarizations for different target temperatures. To understand the influence of laser-polarization and sample temperature on signal intensity, we calculated the plasma temperature (PT) and electron density (ED) . The change in PT and ED was consistent with the change in the atomic lines as the laser polarization was being adjusted. When raising the Cu temperature, the PT increased while the ED decreased. Raising the Cu temperature whilst adjusting the laser-polarization is effective for improving the signal of femtosecond LIBS compared to raising the initial sample temperature alone or only changing the laser polarization.

Optimizing the Rydberg EIT spectrum in a thermal vapor.

We present Rydberg-state electromagnetically-induced-transparency (EIT) measurements examining the effects of laser polarization, magnetic fields, laser intensities, and the optical density of the thermal 87Rb medium. Two counter-propagating laser beams with wavelengths of 480 nm and 780 nm were employed to sweep the spectrum across the Rydberg states |33D3/2〉 and |33D5/2〉. An analytic transmission expression well fits the Rydberg-EIT spectra with multiple transitions under different magnetic fields and laser polarization after accounting for the relevant Clebsch-Gordan coefficients, Zeeman splittings, and Doppler shifts. In addition, the high-contrast Rydberg EIT can be optimized with the probe laser intensity and optical density. Rydberg EIT peak height was achieved at 13%, which is more than twice as high as the maximum peak height at room temperature. A quantitative theoretical model is employed to represent the spectra properties and to predict well the optimization conditions. A Rydberg EIT spectrum with high contrast in real time can be served as a quantum sensor to detect the electromagnetic field within an environment.

Effect of laser polarization on molecular emission from femtosecond LIBS

The study indicates that the intensities of molecular emission bands under circular polarization in femtosecond LIBS are higher than those under linear polarization. The change becomes more evident as the laser energy increases.

Effect of Laser Polarization on Photoionization Efficiency of Lutetium

The effect of laser radiation polarization on the photoionization of lutetium is studied using three-stage scheme 5d6s2 2D3/2-5d6s6p 4Fo5/2-5d6s7s 4D3/2- (53375 cm-1)o1/2. It is shown that in a number of cases, there is a limitation of photoionization associated with the features of coherent photoexcitation. Keywords: laser selective photoionization, lutetium-177.

The effects of laser polarization and wavelength on injection dynamics of a laser wakefield accelerator

Here, we investigate the effects of laser polarization and wavelength on electron injection dynamics in a laser wakefield accelerator. During the ionization process, electrons gain residual momentum and kinetic energy via above threshold ionization, which has a strong dependence on laser polarization. A circularly polarized laser pulse results in a much higher residual momentum and kinetic energy gain for the ionized electrons compared with the linearly polarized case. This residual momentum results in particle injection because of the sensitivity of particle trapping to the initial conditions and enhanced the total injected beam charge in both experiments and particle-in-cell simulations. Due to the strong correlation of above threshold ionization with laser wavelength, in this work we extended the investigation to long wavelength (up to 20 μm) drive pulses using particle-in-cell simulations. Owing to the gain in kinetic energy, it may be expected that the charge trapped would consistently increase for circular polarization with increasing laser wavelength, but this was not observed. Instead, there are oscillations with wavelength in the relative trapped charge between linear and circular polarization cases, which arise because of ionization and heating effects on the plasma. Our studies highlight the complex interplay between several different physical effects, including injection regimes—above threshold ionization assisted injection, wave-breaking injection by carrier-envelope-phase effects and ionization injection—ionization gradient induced laser pulse evolution, and thermal modifications to the wake structure that need considering when extrapolating laser wakefield acceleration to different wavelength regimes.

Laser polarization effect on ion acceleration in laser-cluster interaction

The interaction of high-intensity laser pulses with homo-nuclear aluminum clusters carried out by 2D3V UMPIC code has been investigated. The qualitative picture of the ion acceleration depends on the strength of the laser field and the cluster radius. In this study, the radius of the cluster and the laser dimensionless amplitude has been changed, and the effect of laser polarization on ion acceleration by these variations has been considered. Increasing cluster radius (from 10 to 200 nm), simulations show transferred laser energy to the ions increases for both linear and circular polarization, but the magnitude of this growth for circular polarization is larger than that of linear polarization in a given laser intensity. Also, the effect of laser dimensionless amplitude on ion acceleration has been studied for both laser polarizaton. Simulation reveals that aluminum ions cut-off energy and their energy spread increase rapidly up to a0∼2.5, and then saturate at larger amplitudes, for both polarizations. However, by increasing laser amplitude (a0>5), energy spread of linear polarization is less than that of circular polarization.

Evolution of micro/nano-structural arrays on crystalline silicon carbide by femtosecond laser ablation

An experimental study is conducted to investigate the multi-length scale evolution from micro/nano-structural arrays to V-grooves by femtosecond laser-irradiations, considering the effects of laser polarization and the number of scans on the periodic features and the micro/nano-structures. It is found that the evolution from micro/nano-structural arrays to V-grooves is gradual as the laser fluence, scan speed or the number of scans is increased. Laser-induced surface instability, hatching effects, Coulomb explosions, melting, and evaporation are found to be the underlying mechanisms for the micro/nano structural formation. As the laser fluence increases, the agglomerated nanoparticles change from sparse to dense, so that the boundary between the LIPSS (laser-induced periodic surface structures) becomes less obvious. The oxygen (O) elements attached to the surface of nanoparticles increase with an increase in laser fluence. A high-spatial-frequency LIPSS (HSFL) can transform to low-spatial-frequency LIPSS (LSFL) as the laser fluence excesses the ablation threshold, while the spatial period of the HSFL and LSFL is independent of fluence. It is shown that the irradiated surface evolves from a near-damage-free zone to one with a recast layer and thermal-induced micro-cracks, defined as heat-affected zones (HAZ). Near thermal damage-free micro/nano-structural arrays with different orientations on the sidewalls of the grooves are fabricated at close to the laser ablation threshold by multi-pass scanning. A self-organizing model is developed which shows that laser polarization leads to the asymmetry of energy distribution and the structural array is arranged along the main direction of energy flow. The model analysis shows a good agreement with experimental results and provides an efficient means to understand the interaction between femtosecond laser and silicon carbide (SiC).

Laser ellipticity-dependent supercontinuum generation by femtosecond laser filamentation in air.

We experimentally investigate the laser polarization effect on the supercontinuum (SC) generation through femtosecond laser filamentation in air. By tuning filamenting laser ellipticity from linear polarization to circular polarization, the spectral intensity of the SC after filamentation gradually increases, while the spectral bandwidth of the SC continuously decreases. The laser ellipticity-dependent spectral intensity modulation of the SC is stronger at higher filamenting pulse energy. Laser energy deposits more in linearly polarized laser filaments than in circularly polarized laser filaments. The experimental results are supported by numerical simulations. A physical picture based on the laser ellipticity-dependent clamped intensity inside the filament, together with the Kerr nonlinearity and plasma related self-phase modulations, is proposed to explain the observation.

Effect of Laser Polarization on Fiber Bragg Grating Fabry-Perot Interferometer for Ultrasound Detection

High-finesse fiber Bragg gratings (FBGs) Fabry-Perot interferometers (FPIs) have shown great promise as sensitive ultrasonic sensors. However, the fabrication process of the sensors usually introduces birefringence to the fiber, which makes the sensor operation sensitive to the polarization of the probe laser. Here, we theoretically study the effect of laser polarization on the sensitivity of the sensor with birefringence. We show that, to maintain the sensitivity above half of its maximum of a high-finesse FBG-FPI sensor, the spectral notch separation caused by sensor birefringence should be less than ~61% of the spectral notch width of the sensor. We fabricate an FBG-FPI sensor with negligible overall birefringence by rotating the fiber by 90° between the fabrication of the two FBGs. As a result, the birefringence introduced during the fabrication of the two FBGs cancels out each other. For comparison, a regular FBG-FPI fabricated without fiber rotation was also tested. While the regular FBG-FPI exhibited large variations in detection sensitivity with laser polarization, the polarization-insensitive showed little changes. As a result, no control on the laser polarization is needed during the operation of the polarization-insensitive FBG-FPI for ultrasonic detection, an important attribute required in many practical applications of the sensor.

Effect of laser polarization and target location on acceleration of electrons generated during ionization of gases by a laser pulse

We investigate the effect of the target position, laser polarization, and focusing on the energy spread and the angle of emittance for the acceleration of electrons generated during the ionization of rarefied gases, neon ions Ne8+, krypton ions Kr32+, and argon ions Ar16+ by a laser pulse. The electrons generated from the ions at the position after laser focus interact with the laser pulse for a longer duration and gain more energy than those electrons generated from the ions at the position before laser focus. There are two peaks in the energy spectrum for linear polarization and only one peak for circular polarization. The energy spectrum peak is sharper for circular polarization than that for linear polarization. The energy gained by the electrons increases with the laser spot size due to the increase in the laser energy. The spectrum of the angle of emittance for electrons shows the sharpest peak at the lowest angle for linear polarization for ions at the position after laser focus. The circular polarization is good to obtain quasi-monoenergetic electron beams and linearly polarized laser pulse is good to generate collimated electron beams. The required laser intensity to ionize electrons from the ions Ne8+, Kr32+, and Ar16+ increases and the electron energy peaks are at higher energies and scattering angles are at lower values for these gases, in their respective orders.

Effect of laser polarization on the electron dynamics and photon emission in near-critical-density plasmas

When the laser intensity approaches 1022 W cm−2, the recoil force from high-energy photons radiated by relativistic electrons becomes important and may be comparable with the ponderomotive force of the laser pulse. As a result, the electron dynamics are modified greatly. By using particle-in-cell simulations, we show that the polarization of laser pulse has significant influence on the electron behaviors and accompanying radiation in near-critical-density plasmas. Due to the RR force and the pinching effect of self-generated magnetic field, it turns out that much more electrons are trapped in the center of a circularly-polarized (CP) laser pulse than that of a linearly-polarized (LP) laser pulse. Meanwhile, the γ−photon emission is characterized by a two-peak structure in the LP case, while it is dominated in the forward direction in the CP case where electrons keep moving forward along the laser propagating direction. These may serve as a potential signature for radiation trapping effect in forthcoming experiments to be carried out on petawatt laser facilities.

Influence of polarization on back-reflected e−e+ pair jets from laser-electron collision

We investigate the effect of laser polarization on spatial and momentum distribution of back-reflected e−e+ pairs from the collision of an intense laser pulse (I = 5 × 1022 W cm−2) with a counter-propagating 5 GeV electron beam. During the pair production, a significant amount of particles (106–107) are ejected in the opposite direction of the incoming electron beam (back-reflected), they are trapped by and co-propagate with the laser beam, gaining energy up to the GeV level. From our multi-dimensional particle-in-cell studies, we observe that laser polarization affects the angular distribution of these particles: a linearly polarized pulse produces two transversely separated particle jets, while a circular one leads to the formation of a radially symmetric cone-shaped emission. The results presented here add insights for future experiments performed at multi-PW laser facilities.

Effect of laser polarization on strong-field ionization and fragmentation of nitrous oxide molecules**Project supported by the National Natural Science Foundation of China (Grant Nos. 11534004, 11874179, and 11704149) and the Natural Science Foundation of Jilin Province, China (Grant No. 20180101289JC).

Ionization of molecules in femtosecond laser fields is the most fundamental and important step of various strong-field physical processes. In this study, we experimentally investigate strong field ionization of linear N2O molecules using a time-of-flight mass spectrometer in 800-nm laser fields. Yields of the parent ion and different fragment ions are measured as a function of laser intensity in the range of 2.0×1013 W/cm2 to 3.6×1014 W/cm2. We also investigate the dependence of strong field ionization and dissociation of N2O on laser ellipticity and polarization direction. The significant role of laser induced electron re-collision in the formation of highly charged fragment ions is proved. The physical mechanism of strong field ionization and fragmentation is discussed, based on our experimental results.

Effects of laser polarization and wavelength on hybrid laser wakefield and direct acceleration

We demonstrate that hybrid laser wakefield and direct acceleration can be significantly improved by using two laser pulses with different polarizations or frequencies. The improvement entails higher energy and charge of the accelerated electrons, as well as weaker sensitivity to the time delay between the leading (pump) pulse responsible for generating the wakefield, and the trailing laser pulse responsible for direct laser acceleration (DLA). When the two laser pulses have the same frequency, it is shown that it is advantageous to have their polarization states orthogonal to each other. A specific scenario of a frequency-doubled (λDLA = λpump/2) DLA laser pulse is also considered, and found to be an improvement over the single-frequency (λDLA = λpump) format.

Effects of laser polarization and linear surface features on nanoparticle synthesis during laser ablation in liquids

We elucidate non-isotropic interactions present during laser ablation of ridged surface features under linearly-polarized light and their effect on nanoparticle synthesis via the laser ablation in liquid method. A relationship between the relative polarization/ridge orientation and ablation processes was established by measuring cavitation bubble kinetics, examining the morphology of the ablated surface, and evaluating nanoparticle size distribution. Anisotropic behavior was observed, and this is attributed to selective heating of linear surface structures as confirmed with rigorous coupled-wave analysis. When the incident electric field is aligned parallel to the linear ridges on the target surface, the resulting nanoparticle distributions are much more monodisperse. This phenomenon has a strong influence in the polydispersity and batch-to-batch reproducibility in laser ablation in liquid.