High-intensity Laser Research Articles

High-intensity laser therapy (class IV) and ibuprofen gel phonophoresis for treating knee osteoarthritis among people living in hilly terrain: a randomized, double blind, multi-centre trial protocol

INTRODUCTION: People living in hilly terrain with abnormal cyclic loading could lead to bone cartilage degeneration. High-intensity laser therapy (HILT) and Ibuprofen gel phonophoresis (IGP) have innumerable benefits for patients with knee osteoarthritis (KOA). However, it is still unclear which treatment is effective among them in rehabilitating patients with KOA. OBJECTIVE: To verify whether 8-week HILT is no worse than the IGP in treating patients with knee osteoarthritis living in hilly terrain. MATERIALS AND METHODS: A total of 108 individuals with KOA will be recruited by simple random sampling to participate in a randomized, double-blind, controlled study. Recruited individuals with KOA will be randomly divided into two groups, the HILT group (experimental group) and the IGP group (active control group). The treatment duration of HILT and IGP will be 8 minutes in one session/knee joint for each day for 3 days/week up to 8 weeks in addition to their conventional exercises for 30 minutes. The Western Ontario and McMaster Universities Osteoarthritis Index, Digitalized pain pressure algometer, and 36-Item Short-Form Health Survey questionnaire are the outcome measures that will be recorded at baseline, end of the 8-week post-intervention period. PERSPECTIVES: The results from this trial will contribute to evidence-based recommendations for the clinical implication of whether HILT is no worse than IGP, along with exercise intervention for treating individuals with KOA living in hilly terrain. Trial Registry: Clinical Trials Registry (NCT04320914)

Breakdown of the single-collision condition for soft x-ray high harmonic generation in noble gases

High harmonic generation (HHG) in atomic gases is generally assumed to originate from photoelectrons that are not perturbed by neighboring particles. In this paper, we study theoretically and experimentally the regime where this approximation breaks down. At high laser intensities, we experimentally find that producing soft x-rays beyond this single-collision condition leads to a strong reduction of the coherent HHG response and appearance of incoherent radiation. We generalize our results to phase-matched HHG with mid-infrared drivers, and determine that a minimum pulse energy is needed to simultaneously phase match the HHG process and keep photoelectrons unperturbed by surrounding particles. Therefore, while previous research showed that HHG efficiency is independent of the driving pulse energy if other experimental parameters are scaled accordingly, we find that this rule no longer applies for high photon energies. Our study thus provides important guidelines for the laser parameters needed for the generation of high flux soft x-ray high harmonics.

HIGH-INTENSITY LASER THERAPY TO TREAT NEUROPATHIC PAIN IN POST-HERPETIC NEURALGIA

Post-herpetic neuralgia (PHN) is chronic neuropathic pain that is felt for at least 3 months or more at the site of the rash due to herpes zoster infection. Epidemiological studies get a prevalence of 0.49 cases of PHN per 1000 people per year. The clinical manifestation of PHN is chronic pain on the skin lesions due to herpes zoster infection. The therapy that is commonly used as the first line is the provision of pharmacotherapy such as gabapentin or pregabalin. An 83-year-old male patient with a diagnosis of PHN that had been felt for 5 years. He has been taking drugs for 5 years but the pain has not improved. The patient is given high-intensity laser therapy. After 5 treatments with an interval of 1-2 weeks, pain was significantly reduced from an 8/10 scale to 4/10. The frequency of occurrence of severe pain is also reduced from 5 times per day to only 1 time per day. The use of high-intensity laser therapy is not commonly used as a therapy for PHN. Based on its mechanism of action, the use of high-intensity laser therapy is worth considering because of its effectiveness in treating pain in a shorter time than low-intensity laser therapy.

Topological structure effects of Laguerre-Gaussian laser on self-collimation acceleration mechanism

Energetic plasma beams can be generated through the interaction between a short-pulse high-intensity laser and solid target. However, obtaining collimated plasma beams with low divergence remains challenging. In this study, we devised a self-collimation scheme driven by a topologically structured Laguerre–Gaussian (LG) laser that irradiates a thin target in three-dimensional particle-in-cell simulations. It was observed that a high-density and narrow plasma beam could be formed by the intrinsic hollow intensity distribution of the LG laser. A magnetic tunnel was generated around the beam and collimated the plasma beam within a radius of hundreds of nanometers. This collimation can be enhanced by increasing the topological charge from l = 1 to l = 3 and then destroyed for a larger l. The collimation method is promising in applications requiring well-collimated energetic plasma beams, such as indirect drive inertial con-finement fusion, laboratory astrophysics, and radiation therapy.

Enhanced stimulated Raman scattering during intense laser propagation.

Stimulated Raman scattering is ubiquitous in many high-intensity laser environments. Parametric four-wave mixing between the pump and Raman sidebands can affect the Raman gain, but stringent phase matching requirements and strongly nonlinear dynamics obscure clear understanding of its effects at high laser powers. Here we investigate four-wave mixing in the presence of strong self-focusing and weak ionization at laser powers above the Kerr critical power. Theoretical analysis shows that the plasma generated at focus naturally leads to phase matching conditions suitable for enhanced Raman gain, almost without regard to the initial phase mismatch. Multidimensional nonlinear optical simulations with multiphoton and collisional ionization confirm the enhancement and suggest that it may lead to significantly higher Raman losses in some high-intensity laser environments.

In Vitro Effect of a High-Intensity Laser on Candida albicans Colony Count.

Introduction: This study assessed the effect of a high-intensity laser on Candida albicans colony count. Methods: This in vitro, experimental study was conducted on standard-strain C. albicans (ATCC18804). Seventy-two samples with two different concentrations of C. albicans (104 cells/mL and 106 cells/mL) were randomly assigned to three groups of control, laser and nystatin. Each group included 12 samples from each concentration. In the nystatin group, 10 cc of nystatin suspension was added to the samples and mixed for 30-60 seconds. In the laser group, the Ga-Al-Ar diode laser with a 940-nm wavelength and 2-W power was irradiated to the samples with 0.4 mm tip diameter in non-contact mode (1-mm distance) at a speed of 1 mm/s. The suspensions in the three groups were cultured on the Sabouraud dextrose agar culture medium and incubated at 37°C for 24 hours. The number of C. albicans colonies was then counted and reported. The three groups were compared by ANOVA and Tukey's test (alpha=0.05). Results: In both concentrations, the mean colony count in the nystatin group was significantly lower than that in the control (P<0.05) and laser (P<0.05) groups. The mean colony count in the laser group was significantly lower than that in the control group (P<0.05). Conclusion: The high-intensity laser with a 940-nm wavelength and 2-W power in non-contact mode can significantly decrease the C. albicans colony count in vitro, but its effect is lower than that of nystatin.

Opto-thermal dynamics of thin-film optical limiters based on the VO2 phase transition

Protection of human eyes or sensitive detectors from high-intensity laser radiation is an important challenge in modern light technologies. Metasurfaces have proved to be valuable tools for such light control, but the actual possibility of merging multiple materials in the nanofabrication process hinders their application. Here we propose and numerically investigate the opto-thermal properties of plane multilayered structures with phase-change materials for optical limiters. Our structure relies on thin-film VO2 phase change material on top of a gold film and a sapphire substrate. We show how such a multi-layer structure can act as a self-activating device that exploits light-to-heat conversion to induce a phase change in the VO2 layer. We implement a numerical model to describe the temporal evolution of the temperature and transmittivity across the device under both a continuous wave and pulsed illumination. Our results open new opportunities for multi-layer self-activating optical limiters and may be extended to devices based on other phase change materials or different spectral regions..

Laser Therapy in Perianal Fistulas

(1) Background: Perianal fistula represents a chronic local suppuration, and recurrent or incorrectly treated, this pathology has a negative effect on the life of patients. (2) Methods: A 12-month prospective study was conducted with a study group (patients at the second presentation) and a control group (patients at the first presentation). The BTL-6000 brand laser has 50 times the maximum power of conventional laser devices with an unmatched wavelength of 1064 nm and a tissue penetration power of up to 10 cm. It is highly effective in speeding up healing and pain management (3) Results: Transcutaneous high-intensity laser therapy of perianal fistulas proved effective with a promising positive impact on both symptomatology and local signs in the study group. As for the patients in the control group, 37 of them required a second hospitalization due to the recurrence of symptoms and to whom the same laser therapy was applied. (4) Conclusions: A beneficial and positive effect was observed in our study, mainly on the symptoms determined by the appearance of the perianal fistula, both in the short- and long-term. High-frequency laser therapy is of major importance, considering the lower costs compared to surgery as well as the discomfort created during local treatments.

The Motion of a Charged Particle in the Electromagnetic Field of a Polarization-Modulated Wave

This article presents an exact solution of the equation of motion of a charged particle in the electromagnetic field of a high-intensity polarization-modulated wave. Expressions for the average kinetic energy of a particle without regard to its rest energy in the case of circular and linear polarization of a modulated wave are obtained. The motion of a charged particle in the field was analyzed and expressed in terms of dependences of its average kinetic energy on the electromagnetic wave intensity and on various types of modulation depths. The contribution of each type of modulation to the energy characteristics of a charged particle was demonstrated. Solving the equation of motion of a charged particle in the electromagnetic field of a plane wave opens up possibilities for various applications related, in particular, to various developments of multi-frequency lasers and laser modulation technology. This study was proposed due to the growing interest in experiments using high-intensity femtosecond laser radiation and high-temperature plasma

Development of a hardened THz energy meter for use on the kilojoule-scale, short-pulse OMEGA EP laser.

A highly adaptable and robust terahertz (THz) energy meter is designed and implemented to detect energetic THz pulses from high-intensity (>1018 W/cm2) laser-plasma interactions on the OMEGA EP. THz radiation from the laser driven target is detected by a shielded pyrometer. A second identical pyrometer is used for background subtraction. The detector can be configured to detect THz pulses in the 1mm to 30μm (0.3- to 10-THz) range and pulse energies from joules to microjoules via changes in filtration, aperture size, and position. Additional polarization selective filtration can also be used to determine the THz pulse polarization. The design incorporates significant radiation and electromagnetic pulse shielding to survive and operate within the OMEGA EP radiation environment. We describe the design, operational principle, calibration, and testing of the THz energy meter. The pyrometers were calibrated using a benchtop laser and show linear sensitivity to up to 1000 nJ of absorbed energy. The initial results from four OMEGA EP THz experiments detected up to ∼15μJ at the detector, which can correspond to hundreds of mJ depending on THz emission and reflection models.

Orientation‐Dependent Photoion Emission from Aerosolized Nanostructures

AbstractThe laser‐irradiated aerosolized nanostructures with complex geometries offer unique opportunities to steer orientation‐dependent photoion emission for multiple applications of directional ion sources and photocatalysis. The orientation‐dependent photoion emission is characterized by measuring the distribution and probability on differently oriented nanostructures. This unique capability is achieved by introducing momentum‐to‐space orientation discrimination in the single‐shot velocity map imaging technique with the aerodynamic lens. The effect of geometry, polarization, and concentration to control the photoion emission from differently oriented nanostructures is introduced for optimizing the potential applications of photoion emission including directional tunable nanoanode and optical sensors. The mechanism behind controlling the photoion emission is visualized by the variations in the regions of high laser intensity inside the nanostructures responding to the orientation, geometry, and polarization. This work represents an advance in characterizing the photoion emission from the randomly oriented aerosolized nanostructures and facilitates the potential for combining with the pump–probe methods to provide an intuitive understanding of their real‐time ionization dynamics.

A Comprehensive Review on Amplification of Laser Pulses via Stimulated Raman Scattering and Stimulated Brillouin Scattering in Plasmas

The demand for high-intensity lasers has grown ever since the invention of lasers in 1960, owing to their applications in the fields of inertial confinement fusion, plasma-based relativistic particle accelerators, complex X-ray and gamma-ray sources, and laboratory astrophysics. To create such high-intensity lasers, free-running lasers were either Q-switched or mode-locked to increase the peak power to the gigawatt range. Later, chirped pulse amplification was developed, allowing the generation of peak power up to 1012 W. However, the next generation of high-intensity lasers might not be able to be driven by the solid-state technology alone as they are already operating close to their damage thresholds. In this scenario, concepts of amplification based on plasmas has the potential to revolutionize the laser industry, as plasma is already a broken-down medium, and hence does not pose any problems related to the damage thresholds. On the other hand, there are many other aspects that need to be addressed before developing technologies based on plasma-based amplification, and they are being investigated via theoretical and numerical methods and supported by several experiments. In this report, we review the prospects of employing plasma as the medium of amplification by utilising stimulated scattering techniques, such as the stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) techniques, to modulate high-power laser pulses, which would possibly be the key to the next generation of high-power lasers. The 1980s saw the commencement of research in this field, and possibilities of obtaining high peak powers were verified theoretically with the help of numerical calculations and simulations. The extent of amplification by these stimulated scattering schemes are limited by a number of instabilities such as forward Raman scattering (FRS), filamentation, etc., and here, magnetised plasma played an important role in counteracting these parasitic effects. The current research combines all these factors to experimentally realise a large-scale plasma-based amplifier, which can impact the high-energy laser industry in the near future.

Femtosecond laser hybrid processing strategy of transparent hard and brittle materials.

With high hardness, high thermal stability, chemical inertness and excellent optoelectronic properties, transparent hard and brittle materials have drawn significant attentions in frontier domains such as aerospace, photoelectric detection, and high-intensity lasers. Femtosecond laser processing technology demonstrates great potential for transparent hard and brittle materials processing due to its outstanding advantages such as non-contact, true 3D processing and programmable design. However, high-energy laser ablation usually causes severe damage to the surface of the materials, resulting in low processing accuracy, low processing efficiency and poor surface quality. Femtosecond laser hybrid processing strategies have been proven to be an effective solution to solve the above problems. This mini-review summarizes the fundamentals and research progress of femtosecond laser hybrid processing strategies of transparent hard and brittle materials in recent years. Moreover, the challenges and application prospects of these techniques are discussed.

Femtosecond-Terawatt Hard X-Ray Pulse Generation with Chirped Pulse Amplification on a Free Electron Laser.

Advances of high intensity lasers have opened up the field of strong field physics and led to a broad range of technological applications. Recent x-ray laser sources and optics development makes it possible to obtain extremely high intensity and brightness at x-ray wavelengths. In this Letter, we present a system design that implements chirped pulse amplification for hard x-ray free electron lasers. Numerical modeling with realistic experimental parameters shows that near-transform-limit single-femtosecond hard x-ray laser pulses with peak power exceeding 1TW and brightness exceeding 4×10^{35} s^{-1} mm^{-2} mrad^{-2}0.1% bandwdith^{-1} can be consistently generated. Realization of such beam qualities is essential for establishing systematic and quantitative understanding of strong field x-ray physics and nonlinear x-ray optics phenomena.

Absorption and Transport Effects Induced in Plasmas by the Interaction of Electrons with Laser Speckles.

We show that the ponderomotive force associated with laser speckles can scatter electrons in a laser-produced plasma in a manner similar to Coulomb scattering. Analytic expressions for the effective collision rates are given. The electron-speckle collisions become important at high laser intensity or during filamentation, affecting both long- and short-pulse laser intensity regimes. As an example, we find that the effective collision rate in the laser-overlap region of hohlraums on the National Ignition Facility is expected to exceed the Coulomb collision rate by 1 order of magnitude, leading to a fundamental change to the electron transport properties. At the high intensities characteristic of short-pulse laser-plasma interactions (I≳10^{17} W cm^{-2}), the scattering is strong enough to cause the direct absorption of laser energy, generating hot electrons with energy scaling as E≈1.44(I/10^{18} W cm^{-2})^{1/2} MeV, close to experimentally observed results.

Investigation of the Langdon effect on the nonlinear evolution of SRS from the early-stage inflation to the late-stage development of secondary instabilities

In a laser-irradiated plasma, the Langdon effect can result in a super-Gaussian electron energy distribution function (EEDF), imposing significant influences on stimulated backward Raman scattering (SRS). In this work, the influence of a super-Gaussian EEDF on the nonlinear evolution of SRS is investigated by the three wave coupling model simulation and Vlasov–Maxwell simulation for plasma parameters covering a wide range of kλ De from 0.19 to 0.48 at both high and low intensity laser drives. In the early stage of SRS evolution, it is found that besides the kinetic effects due to electron trapping (2018 Phys. Plasmas 25 100702), the Langdon effect can also significantly widen the parameter range for the absolute growth of SRS, and the time for the absolute SRS to reach saturation is greatly shortened by the Langdon effect within certain parameter regions. In the late stage of SRS, when secondary instabilities such as decay of the electron plasma wave to beam acoustic modes, rescattering, and Langmuir decay instability become important, the Langdon effect can influence the reflectivity of SRS by affecting secondary instabilities. The comprehension of the Langdon effect on nonlinear evolution and saturation of SRS would contribute to a better understanding and prediction of SRS in inertial confinement fusion.

Modeling the x-ray enhancement in foams for laser-driven soft x-ray sources

This paper investigates the mechanism that causes x-ray enhancement in high-Z foams for laser-driven soft x-ray sources. By simulation of one-dimensional radiation-hydrodynamics, it is found that the x-ray enhancement is mainly due to the effect that, in a foam target, shock wave compression significantly reduces the energy loss of hydrodynamic motion (kinetic energy). In a solid target this effect is negligible for its low compressibility. Expressions of kinetic energy reduction (ΔE k = E k,solid − E k,foam) are given to model the improvement of the laser-to-x-ray conversion efficiency. The ΔE k given by the model agrees with the simulation result with about a 15% error for foam density 0.07 – 0.3 g/cc and for laser intensity 0.4 × 1015–2.0 × 1015 W cm−2. The model indicates that the x-ray enhancement is more efficient with a lower foam density and higher laser intensity, which is also presented by the simulation results.

Laser-induced thermotherapy of thyroid nodules with ablation of vessels feeding the nodule

Objective. To improve the results of treatment in patients with benign nodular pathology of the thyroid gland (TG) by means of perfecting the technique of minimally invasive treatment with a high-intensive laser under the sonographic control.&#x0D; Materials and methods. An original technique of laser-induces thermotherapy (LITT) of the thyroid nodule with the ablation of the vessels, feeding the nodule was developed and introduced. The procedure was used in the treatment of 91 patients with benign nodular pathology of the thyroid gland, 116 patients underwent laser-induced thermotherapy by the standard technique (comparison group). Three months later, US was used to assess and compare the results of treatment in both groups. The results of thermometry were analyzed depending on the initial volume of the TG nodular neoplasm.&#x0D; Results. A decrease in the nodules with the initial volume up to 2 cm3 in both groups was statistically significant and took place practically similarly 78.7 % in the main group and 71.7 % in the comparison group. When exposing the nodules of larger sizes, the efficiency of standard LITT method fell. In the comparison group, patients with the nodular sizes of 68 cm2 had a decrease in the volume only by 25.8 % % (from 6.74 cm3 to 5.0 cm3). When using an original method of thermoablation (TA), a decrease in the nodules of the same size was 69.3 % (from 6.98 cm3 to 2.14 cm3). The difference was statistically significant (p = 0,003) that proves the efficiency of this technique. In the subgroup with the nodules 8 cm3, a nodular volume decrease was 33.3 % (from 11.05 to 7.36 cm3) in the main group and 28.8 % (from 14.07 to 10.02 cm3) in the comparison group. The difference was not statistically significant (p = 279).&#x0D; Conclusions. Laser-induces thermotherapy of the thyroid gland with the ablation of the vessel, feeding the nodule, leads to a statistically significant reduction of the benign colloid nodular neoplasms of any size. The original technique indicated higher efficiency compared with standard LITT in relation to the nodules sized from 6 to 8 cm.

In vitro recording of muscle activity induced by high intensity laser optogenetic stimulation using a diamond quantum biosensor

The detection of physiological activity at the microscopic level is key for understanding the function of biosystems and relating this to their physical structure. Current sensing methods for in vitro study of living tissue often rely on invasive probes to stimulate and detect activity, bearing the risk of inducing damage in the target system. In recent years, a new type of quantum sensor based on color centers in diamond has begun to offer the possibility to instead passively sense and image living biological systems. Here, we use such a sensor to realize the recording of the biomagnetic field generated by tightly focused, high intensity pulsed laser optogenetic neuromuscular stimulation of extensor digitorum longus muscles, dissected from mice and kept alive in carbogenated solution. Recordings captured a compound action potential response and a slow signal component, which we seek to explain using a detailed model of the biological system. We show proof-of-principle experimental recording of localized neuromuscular activity from the laser stimulation site without photovoltaic or fluorescence artifacts associated with alternative techniques. Our work represents a further step toward passive sensing and imaging at the microscopic level with quantum sensing, enabling further research into mapping of neural activity and intracellular processes.

Shock-Augmented Ignition Approach to Laser Inertial Fusion

Shock ignition enables high gain at low implosion velocity, reducing ablative Rayleigh-Taylor instability growth, which can degrade conventional direct drive. With this method, driving a strong shock requires high laser power and intensity, resulting in inefficiencies in the drive and the generation of hot electrons that can preheat the fuel. A new "shock-augmented ignition" pulse shape is described that, by preconditioning the ablation plasma before launching a strong shock, enables the shock ignition of thermonuclear fuel, but importantly, with substantially reduced laser power and intensity requirements. The reduced intensity requirement with respect to shock ignition limits laser-plasma instabilities, such as stimulated Raman and Brillouin scatter, reducing the risk of hot-electron preheat and restoring the laser coupling advantages of conventional direct drive. Simulations indicate that, due to the reduced power requirements, high gain (∼100) ignition of large-scale direct drive implosions (outer radius ∼1750 μm, deuterium-tritium ice thickness ∼165 μm) may be possible within the power and energy limits of existing facilities such as the National Ignition Facility. Moreover, this concept extends to indirect drive implosions, which exhibit substantial yield increases at reduced implosion velocity. Shock-augmented ignition expands the viable design space of laser inertial fusion.