Ultrashort Pulsed Beams Research Articles

Ultrashort pulsed beam induced nanoparticles displacement trajectories via optical forces in symmetrical and symmetry-breaking systems

Ultrashort pulsed beam induced nanoparticles displacement trajectories via optical forces in symmetrical and symmetry-breaking systems

Transfer Learning For Predictive Quality In Laser-Induced Plasma Micro-Machining

Abstract In laser-induced plasma micro-machining (LIPMM), a focused, ultrashort pulsed laser beam creates a highly localized plasma zone within a transparent liquid dielectric. When the beam intensity is greater than the breakdown threshold in the dielectric media, plasma is formed which is then used to ablate the workpiece. This paper aims to facilitate in-situ process monitoring and quality prediction for LIPMM by developing a deep learning model to (1) understand the relationship between acoustic emission data and quality of micro-machining with LIPMM, (2) transfer such understanding across different process parameters, and (3) predict quality accurately by fine-tuning models with a smaller dataset. Experiments and results show that the relationship learned from one process parameter can be transferred to other parameters, requiring lesser data and lesser computational time for training the model. We investigate the feasibility of transfer learning and compare the performance of various transfer learning models: different input features, different CNN structures, and the same structure with different fine-tuned layers. The findings provide insights into how to design effective transfer learning models for manufacturing applications.

Transfer learning for predictive quality in laser-induced plasma micro-machining

In laser-induced plasma micro-machining (LIPMM), a focused, ultrashort pulsed laser beam creates a highly localized plasma zone within a transparent liquid dielectric. When the beam intensity is greater than the breakdown threshold in the dielectric media, plasma is formed which is then used to ablate the workpiece. This paper aims to facilitate in-situ process monitoring and quality prediction for LIPMM by developing a deep learning model to (1) understand the relationship between acoustic emission data and quality of micro-machining with LIPMM, (2) transfer such understanding across different process parameters, and (3) predict quality accurately by fine-tuning models with a smaller dataset. Experiments and results show that the relationship learned from one process parameter can be transferred to other parameters, requiring lesser data and lesser computational time for training the model. We investigate the feasibility of transfer learning and compare the performance of various transfer learning models: different input features, different CNN structures, and the same structure with different fine-tuned layers. The findings provide insights into how to design effective transfer learning models for manufacturing applications.

Attosecond electron-beam technology: a review of recent progress.

Electron microscopy and diffraction with ultrashort pulsed electron beams are capable of imaging transient phenomena with the combined ultrafast temporal and atomic-scale spatial resolutions. The emerging field of optical electron beam control allowed the manipulation of relativistic and sub-relativistic electron beams at the level of optical cycles. Specifically, it enabled the generation of electron beams in the form of attosecond pulse trains and individual attosecond pulses. In this review, we describe the basics of the attosecond electron beam control and overview the recent experimental progress. High-energy electron pulses of attosecond sub-optical cycle duration open up novel opportunities for space-time-resolved imaging of ultrafast chemical and physical processes, coherent photon generation, free electron quantum optics, electron-atom scattering with shaped wave packets and laser-driven particle acceleration. Graphical Abstract.

Geometric spin Hall effect of a laser beam beyond the paraxial approximation

An intriguing spin-orbital angular momentum interaction, called the geometric spin Hall effect of light (GSHEL), has aroused much interest and manifests itself as a transverse shift. The GSHEL of the classical optical field is independent of the beam size. In this paper the GSHELs of the vortex vector continuous wave (VVCW) and vortex ultrashort pulsed beam (VUPB) are systematically analyzed beyond the paraxial approximation. The analytical expression of the transverse shift of the VVCW is obtained. Evidently, the magnitude of the transverse shift depends on the ratio of the beam waist to the wavelength. The transverse shift can be effectively enlarged by narrowing the beam waist even to the order of more than $10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{m}$. This intriguing phenomenon is caused by the stronger spin-orbital interaction induced energy flow in the nonparaxial regime. Furthermore, the GSHEL of the VUPB is also explored. The pulse duration time strongly affects the distribution of the phase. The singularities play a crucial role in altering the orientation of the electric field. As a result, the VUPBs with different pulse duration time have different magnitudes of the GSHEL. These results may find significant applications in the investigation of the particle manipulation, microscopic imaging, and ultrashort optics.

The Effect of Low-Energy Laser-Driven Ultrashort Pulsed Electron Beam Irradiation on Erythropoiesis and Oxidative Stress in Rats.

Anemia is a commonly observed consequence of whole-body exposure to a dose of X-ray or gamma irradiation of the order of the mean lethal dose in mammals, and it is an important factor for the determination of the survival of animals. The aim of this study was to unravel the effect of laser-driven ultrashort pulsed electron beam (UPEB) irradiation on the process of erythropoiesis and the redox state in the organism. Wistar rats were exposed to laser-driven UPEB irradiation, after which the level of oxidative stress and the activities of different antioxidant enzymes, as well as blood smears, bone marrow imprints and sections, erythroblastic islets, hemoglobin and hematocrit, hepatic iron, DNA, and erythropoietin levels, were assessed on the 1st, 3rd, 7th, 14th, and 28th days after irradiation. Despite the fact that laser-driven UPEB irradiation requires quite low doses and repetition rates to achieve the LD50 in rats, our findings suggest that whole-body exposure with this new type of irradiation causes relatively mild anemia in rats, with subsequent fast recovery up to the 28th day. Moreover, this novel type of irradiation causes highly intense processes of oxidative stress, which, despite being relatively extinguished, did not reach the physiologically stable level even at the 28th day after irradiation due to the violations in the antioxidant system of the organism.

Formulation of diffraction efficiencies of binary phase gratings for array illumination with ultrashort pulse beams.

We present simple formulas for the diffraction efficiencies of a binary phase grating that performs array illumination with ultrashort pulse beams. Using scalar diffraction theory, we formulated the efficiencies as a function of pulse spectral width by Fourier-transforming the complex-modulated frequency spectra of diffracted pulses in the far-field region. From the analytical simulations, we found that pulse array uniformity departs from unity as the spectral width increases, or the pulse duration decreases, thereby limiting the attainable split counts. This finding can be considered in the design of gratings for delivering controlled amounts of pulse energies to diffraction orders of interest.

Low-Energy Laser-Driven Ultrashort Pulsed Electron Beam Irradiation-Induced Immune Response in Rats.

The development of new laser-driven electron linear accelerators, providing unique ultrashort pulsed electron beams (UPEBs) with low repetition rates, opens new opportunities for radiotherapy and new fronts for radiobiological research in general. Considering the growing interest in the application of UPEBs in radiation biology and medicine, the aim of this study was to reveal the changes in immune system in response to low-energy laser-driven UPEB whole-body irradiation in rodents. Forty male albino Wistar rats were exposed to laser-driven UPEB irradiation, after which different immunological parameters were studied on the 1st, 3rd, 7th, 14th, and 28th day after irradiation. According to the results, this type of irradiation induces alterations in the rat immune system, particularly by increasing the production of pro- and anti-inflammatory cytokines and elevating the DNA damage rate. Moreover, such an immune response reaches its maximal levels on the third day after laser-driven UPEB whole-body irradiation, showing partial recovery on subsequent days with a total recovery on the 28th day. The results of this study provide valuable insight into the effect of laser-driven UPEB whole-body irradiation on the immune system of the animals and support further animal experiments on the role of this novel type of irradiation.

Angular momentum of the vortex ultrashort pulsed beam with a smaller beam waist.

The angular momentum (AM) of light has important implications for many fields of optics research, such as optics communication, quantum information and laser-scan microscopy. Thus, in this paper, we intend to investigate the average AM of the vortex ultrashort pulsed beam (VUPB), which is generated and widely applied in the field of high-intensity and ultrafast regimes. According to the vector potential, we firstly derive the electromagnetic field of the VUPB, then analyze the spatial intensity, the phase profile and the polarization state of the beam. We explore that the total AM per photon of VUPB is not n ℏ value when the beam waist w0 is of wavelength or sub-wavelength order, since the polarization of VUPB is changed from linear to circular polarization with the decrease of beam waist, which introduces the conversion of the orbital AM to the spin AM. Moreover, based on the conservation of the total AM, the minimum waist of VUPB can be obtained, which is dependent on the pulse duration time α and topological charge n. Finally, the average AM of the fractional VUPB expressed by the superposition of the integer VUPB with different weights, is analyzed, which is not equal to the AM of fractional CW beam μ - sin (2μπ)/2π (μ is the fractional topological charge), but is associated with the beam waist w0 and α. Therefore, we think that the AM of VUPB can be controlled by adjusting the α and w0.

Comparing the efficacy of γ- and electron-irradiation of PBMCs to promote secretion of paracrine, regenerative factors

Cell-free secretomes represent a promising new therapeutic avenue in regenerative medicine, and γ-irradiation of human peripheral blood mononuclear cells (PBMCs) has been shown to promote the release of paracrine factors with high regenerative potential. Recently, the use of alternative irradiation sources, such as artificially generated β- or electron-irradiation, is encouraged by authorities. Since the effect of the less hazardous electron-radiation on the production and functions of paracrine factors has not been tested so far, we compared the effects of γ- and electron-irradiation on PBMCs and determined the efficacy of both radiation sources for producing regenerative secretomes. Exposure to 60 Gy γ-rays from a radioactive nuclide and 60 Gy electron-irradiation provided by a linear accelerator comparably induced cell death and DNA damage. The transcriptional landscapes of PBMCs exposed to either radiation source shared a high degree of similarity. Secretion patterns of proteins, lipids, and extracellular vesicles displayed similar profiles after γ- and electron-irradiation. Lastly, we detected comparable biological activities in functional assays reflecting the regenerative potential of the secretomes. Taken together, we were able to demonstrate that electron-irradiation is an effective, alternative radiation source for producing therapeutic, cell-free secretomes. Our study paves the way for future clinical trials employing secretomes generated with electron-irradiation in tissue-regenerative medicine.

Achromatic optical system with diffractive-refractive hybrid lenses for multifocusing of ultrashort pulse beams.

We report an achromatic cascade optical system for multifocusing ultrashort pulse beams with a diffractive beam splitter. Distortion compensation requires the removal of pulse front distortions from arrayed pulses, which originate from beam-radius-dependent group delay dispersions. The inclusion of hybrid diffractive-refractive lenses can effectively manage system dispersions. Simple design formulas are derived using the ray-matrix analysis and the designed system is evaluated using 20-fs pulses. We confirm that the hybridized system can remove not only chromatic aberrations but also pulse front distortions, hence improving the system spatio-temporal focusing resolutions. The proposed pulse delivery technique enhances the practicality of materials processing with ultrashort pulses.

Low Repair Capacity of DNA Double-Strand Breaks Induced by Laser-Driven Ultrashort Electron Beams in Cancer Cells.

Laser-driven accelerators allow to generate ultrashort (from femto- to picoseconds) high peak dose-rate (up to tens of GGy/s) accelerated particle beams. However, the radiobiological effects of ultrashort pulsed irradiation are still poorly studied. The aim of this work was to compare the formation and elimination of γH2AX and 53BP1 foci (well known markers for DNA double-strand breaks (DSBs)) in Hela cells exposed to ultrashort pulsed electron beams generated by Advanced Research Electron Accelerator Laboratory (AREAL) accelerator (electron energy 3.6 MeV, pulse duration 450 fs, pulse repetition rates 2 or 20 Hz) and quasi-continuous radiation generated by Varian accelerator (electron energy 4 MeV) at doses of 250–1000 mGy. Additionally, a study on the dose–response relationships of changes in the number of residual γH2AX foci in HeLa and A549 cells 24 h after irradiation at doses of 500–10,000 mGy were performed. We found no statistically significant differences in γH2AX and 53BP1 foci yields at 1 h after exposure to 2 Hz ultrashort pulse vs. quasi-continuous radiations. In contrast, 20 Hz ultrashort pulse irradiation resulted in 1.27-fold higher foci yields as compared to the quasi-continuous one. After 24 h of pulse irradiation at doses of 500–10,000 mGy the number of residual γH2AX foci in Hela and A549 cells was 1.7–2.9 times higher compared to that of quasi-continuous irradiation. Overall, the obtained results suggest the slower repair rate for DSBs induced by ultrashort pulse irradiation in comparison to DSBs induced by quasi-continuous irradiation.

Investigation on fiber laser irradiation of transparent polycarbonate

The study aims to understand the carbonization mechanism when an ns NIR transparent fiber laser beam irradiation of polycarbonate (PC) instead of irradiation using a UV laser beam or ultrashort pulsed laser beam. It reveals that PC can be decomposed with an ns transparent 1064 nm laser beam. The laser fluence threshold under which to cause ablation in PC was not a constant value. The threshold decreased as the scanning pulse number increased. The threshold fluence was above 2.9 J/cm2 at irradiation with 10 pulses. The threshold fluence was above 11.6 mJ/cm2 at irradiation with 2 pulses. The optical transmittance of PC was decreased under laser irradiation. The optical transmittance was reduced by 50% and 90% at laser fluence of 2.9 J/cm2 and 11.6 J/cm2, respectively, at irradiation with 15 pulses. In addition, x-ray photoelectron spectroscopy measurements show that the C/O ratio was reduced 20.8% and 33.2%, respectively. The water contact angle was reduced due to the carbon loss at the PC surface. Inside marking of PC produced a darker contrast than surface marking due to that the carbon was lost at the surface, in contrary, carbonate concentration remained when marking inside the bulk of PC.

Broadband spatio-temporal propagation characteristics of Airy plasmons

We experimentally investigate the propagation of Airy surface plasmon polaritons (Airy SPPs) on a gold film by multiphoton Photoemission Electron Microscopy (PEEM) at different excitation wavelengths and compare the result with rigorous numerical simulations. The typical bent trajectories of the excited two-dimensional beams are observed and analyzed over a wide range of wavelengths. We furthermore investigate the generation bandwidth of the diffraction grating from modal overlap calculations and evaluate the possibility of creating ultrashort Airy plasmon pulses. This provides a viable route to engineer two-dimensional ultrashort non-diffracting pulsed beams in the field of ultrafast nanophotonics.

Induced birefringence in glass: depletion and enhancement by orthogonal-polarized femtosecond pulses

We show spectacular and different effect of the sequential and simultaneous writing of two perpendicularly polarized ultrashort laser pulse trains on profile and magnitude of induced optical retardation inside fused silica glass. Clear birefringence was observed in the region exposed to linearly polarized pulse train radiation. It found out that the induced birefringence is erasable. It means that, when the sample is irradiated again with pulse train having perpendicular polarization, the induced birefringence is vanished and can be totally erased by optimizing the pulse energy. However, in a simultaneous writing approach, a contradictory result was observed. When the glass substrates were simultaneously (i.e. with an accuracy better than the pulse duration) exposed to two beams with perpendicular polarization the induced birefringence not only remained but also enhanced. Discussion and study on the results of interaction of polarized single ultrashort laser pulse and sequential laser beams (which spatially overlapped) having different polarizations and also change of energy ratio of simultaneously writing pulse trains helps us to analyze different results of the simultaneous interaction of two orthogonally polarized ultrashort laser pulse trains with transparent material. Our results provide pieces of evidence for further understanding the physical mechanism of creation of the birefringence using ultrashort laser pulses. Additionally, they provide the ability to manipulate the transient electron dynamics to control the profile and tailor of the induced birefringence.

Fractional vortex ultrashort pulsed beams with modulating vortex strength.

In most papers about the fractional vortex continuous beams (FVCBs), the relationship between the total vortex strength Sα and the propagation distance is not analyzed since the vortex structure is not stable in the near field. In this paper, we theoretically study the fractional vortex ultrashort pulsed beams (FVUPBs) possessing non-integer topological charges α at arbitrary plane and find that the vortex structure is propagation-distance-dependent. Both the intensity and phase distributions are calculated to analyze the vortex structure. To evaluate the propagation properties of FVUPBs, we focus on the total vortex strength (TVS) of FVUPBs to investigate the number of vortex, and demonstrate that the birth of a vortex is at α = m + ɛ, where m is an integer, ɛ is a changing fraction depending on the pulse durations, peak wavelengths and propagation distances. Furthermore, we discover that the FVUPBs carry decreasing TVS along the propagation axis in free space. This special vortex structure for FVUPBs appears due to the mixture weight of vortex pulsed beam with different integer topological charges (TCs) n. However, the total orbital angular momentum is invariant during propagation. The above phenomenon presented in our paper are totally particular and intriguing compared with the FVCBs.

Laser-Driven Ultrashort Pulsed Electron Beam Radiation at Doses of 0.5 and 1.0 Gy Induces Apoptosis in Human Fibroblasts.

Rapidly evolving laser technologies have led to the development of laser-generated particle accelerators as an alternative to conventional facilities. However, the radiobiological characteristics need to be determined to enhance their applications in biology and medicine. In this study, the radiobiological effects of ultrashort pulsed electron beam (UPEB) and X-ray radiation in human lung fibroblasts (MRC-5 cell line) exposed to doses of 0.1, 0.5, and 1 Gy are compared. The changes of γH2AX foci number as a marker of DNA double-strand breaks (DSBs) were analyzed. In addition, the micronuclei induction and cell death via apoptosis were studied. We found that the biological action of UPEB-radiation compared to X-rays was characterized by significantly slower γH2AX foci elimination (with a dose of 1 Gy) and strong apoptosis induction (with doses of 0.5 and 1.0 Gy), accompanied by a slight increase in micronuclei formation (dose of 1 Gy). Our data suggest that UPEB radiation produces more complex DNA damage than X-ray radiation, leading to cell death rather than cytogenetic disturbance.

Quasi single-shot two-pulse tilted pulse front autocorrelator coupled with spatial chirp and spectral divergence monitor for ultrashort pulsed laser beams

Simultaneous single-shot unambiguous detection and measurement of pulse front tilt, spatial chirp, spectral divergence and pulse width has been carried out using two-pulse tilted pulse-front autocorrelator (TP-TPFAC) coupled with spectral interferometry using small part of laser beam intercepted from Mach Zehnder delay unit of TP-TPFAC generating two delayed and spatially inverted pulses. Error in estimation of rotation angle of autocorrelation (AC) trace due to accidental improper positioning of CCD detector is avoided by measuring angle between AC traces corresponding to two delayed and spatially inverted pulses. Likewise, accuracy in estimation of spatial chirp is improved by using spatially resolved spectral trace of two spatially inverted pulses, as errors due to accidental improper positioning of either grating of spectrograph or CCD detector are avoided. Sensitivities and accuracies of the two methods are compared in different experimental situations. Estimated pulse parameters are found in close accordance with respective theoretical values.

Ultrashort Bessel beam photoinscription of Bragg grating waveguides and their application as temperature sensors

Ultrashort pulsed Bessel beams with intrinsic nondiffractive character and potential strong excitation confinement down to 100 nm can show a series of advantages over Gaussian beams in fabricating efficient Bragg grating waveguides (BGWs). In this work, we focus on parameter management for the inscription of efficient BGWs using the point-by-point method employing Bessel beams. Due to their high aspect ratio, the resulting one-dimensional void-like structures can section the waveguides and interact efficiently with the optical modes. Effective first-order BGWs with low birefringence can then be fabricated in bulk fused silica. By controlling the size and the relative location of grating voids via the Bessel pulse energy and scan velocities, the resonant behaviors of BGWs can be well regulated. A high value of 34 dB for 8 mm length is achieved. A simple predictive model for BGWs is proposed for analyzing the influences of processing parameters on the performance of BGWs. The technique permits multiplexing several gratings in the same waveguide. Up to eight grating traces were straightforwardly inscribed into the waveguide in a parallel-serial combined mode, forming the multiplex BGWs. As an application, the multiplex BGW sensor with two resonant peaks is proposed and fabricated for improving the reliability of temperature detection.

Three-dimensional carrier-envelope-phase map of focused few-cycle pulsed Gaussian beams

We derive an analytical expression that describes the complete three-dimensional carrier-envelope phase (CEP) distribution of in the focal volume of ultrashort pulsed Gaussian beams focused by spherical mirrors or lenses. The focal CEP map depends on the so-called factor $g$ specifying the frequency-dependence of the beam width of the source few-cycle pulse, on its chirp and on the small chromatic aberration introduced by a lens without appreciably distorting or broadening the few-cycle pulse. We show how to tailor the CEP map of mirror-focused and lens-focused few-cycle pulses in order to produce negligible transversal and axial CEP variations in specific regions of the focal volume for phase-sensitive interactions of light with matter taking place in a volume or on a surface. We propose a quasi-achromatic doublet lens that can implement in practice these tailored CEP distributions.