Narrow Laser Beam Research Articles

Efficacy and safety of sequential treatment with botulinum toxin type A, fractional CO2 laser, and topical growth factor for hypertrophic scar management: a retrospective analysis

Hypertrophic scars arise from aberrant wound healing and can lead to functional and aesthetic impairments. One of the common interventions for treating hypertrophic scars is fractional carbon dioxide (CO2) laser, which employs narrow laser beams to stimulate dermal collagen deposition. Recent studies and reports have suggested that combining laser therapy with other interventions such as botulinum toxin type A (BTX-A) and topical growth factors may enhance treatment outcomes. Here, we examine the efficacy and safety of a sequential combination of BTX-A, fractional CO2 laser, and topical growth factors, referred to as combined therapy, for treating hypertrophic scars compared with only using fractional CO2 laser and topical growth factors, referred to as monotherapy. Our retrospective study includes 128 patients with hypertrophic scars (56 underwent monotherapy and 72 underwent combined therapy), which were followed-up for up to 15 months after the initiation of treatment to collect demographic and clinical data. Our analysis showed that the combined therapy significantly outperformed monotherapy in improving Vancouver scar scale scores (P < 0.05) and in the reduction of scar thickness (P < 0.05), without increasing adverse complications. Repeated treatments further augmented the efficacy of the combined therapy. Subgroup analysis revealed that combined therapy was notably more effective in reducing Vancouver scar scale scores and scar thickness in early-stage scars compared to late-stage (P = 0.023 and P = 0.045, respectively). Our study suggests that including BTX-A treatment before fractional CO2 laser and topical growth factors offers superior efficacy in reducing hypertrophic scars. We encourage early intervention and repeated treatments for optimal treatment outcomes.

Dual-frequency and multi-linewidth laser based on self-injection locking for optical gyroscopes

Diverse resonant optical gyroscopes (ROG) exhibit unique lasers requirements and the optimal method involves integrating multiple functions into a singular laser device. Here, we introduce a simple dual-frequency multi-linewidth laser configuration for resonant optical gyroscopes, which uses self-injection locking technology for frequency stabilization and linewidth narrowing, generating the first narrow linewidth laser beam. Then, based on self-injection locking technology, careful adjustment of the ring cavity length has been used to achieve the second laser with Brillouin frequency shift and further narrowing of laser linewidth. In addition, external phase modulation is performed at another light port by loading the radio frequency voltage signal onto the electro-optic phase modulator to achieve the purpose of spectral broadening, which is the third broad-spectrum laser. Finally, we have successfully applied the proposed dual-frequency multi-linewidth laser in both the narrow-linewidth laser-driven traditional ROG and the broadband laser-driven ROG. This work is of significant importance for improving the versatility of lasers, reducing the testing cost and size of gyroscope. Next, the focus of future work will translate the proposed laser design to integrated photonics.

Pressure estimation via measurement of reduced light scattering coefficient by oblique laser incident reflectometry

Continuous measurement of pressure is vital in many fields of industry, medicine, and science. Of particular interest is the ability to measure pressure in a noninvasive and contact-free manner. This work presents the potential of oblique incident reflectometry (OIR) to monitor variation in pressure via the reduced scattering parameter (μs′). Pressure deforms the geometry of the medium and causes distortion of its internal structure and the spatial distribution of optical properties. Light scattering is related to the morphology (size, density, distribution, etc.) and refractive index distributions of the medium, and applied pressure will influence directly these parameters. Therefore, we assume that pressure can be quantitatively assessed through monitoring the reduced scattering coefficient. For this purpose, the technique of OIR to evaluate the scattering parameter during pressure variations was utilized. OIR is a simple noninvasive and contact-free imaging technique able to quantify both absorption and scattering properties of a sample. In our setup, the medium is illuminated obliquely by a narrow laser beam, and the diffuse reflectance light is captured by a CCD camera. In offline processing, the shift (δ) of the diffuse light center from the incident point is mathematically analyzed and μs′ coefficient (μs′∼δ−1) is extracted. We present here confirmation of the validity of this assumption through results of a series of experiments performed on turbid liquid and artery occlusion of a human subject under different pressure levels. Thus, μs′ has the potential to serve as a good indicator for the monitoring of pressure.

Fermi pencil beams and off-axis laser detection.

This paper concerns the analytic reconstruction of properties for narrow laser beams propagating in turbulent atmospheres. We consider the setting of off-axis measurements based on wide-angle single scattering of light detected away from the main path of the beam. Light propagation in the beam itself is modeled by macroscopic approximations of radiative transfer equations that take the form of Fermi pencil beam or fractional Fermi pencil beam equations. This allows for a simplified reconstruction procedure of the beam's constitutive parameters, in particular, its direction of propagation and the location of the emitting source.

Vertical Cavity Surface Emitting Laser Performance Maturing through Machine Learning for High-Yield Optical Wireless Network.

The high-yield optical wireless network (OWN) is a promising framework to strengthen 5G and 6G mobility. In addition, high direction and narrow bandwidth-based laser beams are enormously noteworthy for high data transmission over standard optical fibers. Therefore, in this paper, the performance of a vertical cavity surface emitting laser (VCSEL) is evaluated using the machine learning (ML) technique, aiming to purify the optical beam and enable OWN to support high-speed, multi-user data transmission. The ML technique is applied on a designed VCSEL array to optimize paths for DC injection, AC signal modulation, and multiple-user transmission. The mathematical model of VCSEL narrow beam, OWN, and energy loss through nonlinear interference in an optical wireless network is studied. In addition, the mathematical model is then affirmed with a simulation model following the bit error rate (BER), the laser power, the current, and the fiber-length performance matrices. The results estimations declare that the presented methodology offers a narrow beam of VCSEL, mitigating nonlinear interference in OWN and increasing energy efficiency.

A Predefined-Time Control for the Laser Acquisition in Space Gravitational Wave Detection Mission.

The establishment of a laser link between satellites, i.e., the acquisition phase, is a key technology for space-based gravitational detection missions, and it becomes extremely complicated when the long distance between satellites, the inherent limits of the sensor accuracy, the narrow laser beam divergence and the complex space environment are considered. In this paper, we investigate the laser acquisition problem of a new type of satellite equipped with two two-degree-of-freedom telescopes. A predefined-time controller law for the acquisition phase is proposed. Finally, a numerical simulation was conducted to demonstrate the effectiveness of the proposed controller. The results showed that the new strategy has a higher efficiency and the control performance can meet the requirements of the gravitational detection mission.

Study of anisotropy of convective optical underwater turbulence and the effect of the mean water temperature in the presence of a varying temperature gradient on it

In this paper, the anisotropy of optical convective underwater turbulence is investigated in terms of the variance of angle of arrival (AOA) fluctuations of a narrow laser beam propagating through it in different sections of the medium. The collimated laser beam with a wavelength 532 nm and a diameter 1 cm, which passes through a convective underwater turbulence. The turbulence is generated in a water tank with dimensions of 20 cm × 36 cm × 20 cm, which is installed on a flat surface electrical heater. During the experiments, the mean water temperature (MWT) can be changed from room temperature to 34 ∘C by increasing the heater temperature. The use of the heater also generates a temperature gradient in the medium. The laser beam propagates along a horizontal path with a length of 20 cm inside the tank at different altitudes from the heater source, as well as at different distances from one of the side walls of the turbulent medium. After passing the laser beam through the turbulent medium, the fluctuations of the AOA components in the vertical and horizontal directions are measured. From the time series of the measured AOA fluctuations, their variances are determined. The anisotropy of the medium is investigated by comparing the variance of AOA components measured in the vertical and horizontal directions. We show that the variances of both of vertical and horizontal components of the AOA fluctuations are increased with the MWT, and they are saturated at higher MWTs. In addition, different anisotropic behaviors are observed for the variances of the measured AOA fluctuations at the vicinity of the lateral wall and upper surface of the water. At the vicinity of the lateral wall the variances of the AOA fluctuations in the horizontal component are larger, but at the vicinity of the upper surface the variances of the AOA fluctuations in the vertical component are dominant. This behavior may be caused by the change of the convection motion direction in the turbulent fluid.

A study on angle of arrival fluctuations in a temperature-, salinity- and sweetness-induced underwater optical turbulence

In this paper, we report the measurement of fluctuations of two components of Angle of Arrival (AoA) of a narrow laser beam propagating through an underwater turbulence induced by a mixture of hot and cold waters having inhomogeneity at small scales, and consider the effect of the water mean temperature on the AoA fluctuations. The same studies on the AoA fluctuations are presented when a mixture of two volumes of water with different salinity and sweetness are used. The results show that the AoA fluctuations increase by increasing the difference in initial temperatures of the hot and cold waters. Comparison of the variances of the AoA fluctuations for two different propagation lengths, reveals that it is greater for the longer path. In addition, comparison of the AoA fluctuations in two directions for different initial temperatures of the cold and hot waters shows that the underwater turbulence is an anisotropic medium whose anisotropy increases with the mean temperature of the water. In the experiments with the mixture of two volumes of water with different salinity and sweetness, the AoA fluctuations are not seriously affected by the water salinity, while for the sweetness we see a small but interesting response.

Short-distance equivalent test of acquisition, pointing, and tracking process for space laser communication.

The function and performance of acquisition, pointing, and tracking (APT) for the space laser communication terminals must be characterized on the ground before the launching. However, short working distance causes the terminals to not be viewed as a point, leading to the challenge for the whole-process equivalent test. A novel equivalent test method is proposed, to the best of our knowledge, by using a narrow laser beam and the imaging relationship between two terminals. The communication terminal is transformed to a virtual point by establishing an imaging relationship between the antenna of the transmitter and the tracking detector of the receiver. Thus, the deviation angle between the optical axis of the receiver and the centroid line of two terminals can be measured accurately. Furthermore, the acquisition process of searching the small-size antenna in the receiver with an extensive coverage beam in the transmitter is replaced by searching a large receiver surface with a narrow beam. This point-searching-surface method is equivalent to the surface-searching-point method in actual space communication. With this method, two terminals spaced 5 m apart were employed to construct the short-distance verification platform, and the APT function verification and performance test were completed.

Refraction by gas inhomogeneities during laser heating of a metal

An analysis is made of the distribution of the refractive index near the boundary of a metal heated by laser radiation. The gradient of the refractive index of the gas, caused by the heat flux, and the distribution of the refractive index in the inhomogeneously heated gas are found. The drift of the laser beam due to the refraction of radiation in a gas is estimated, which shows an increase in the drift for narrow laser beams. Keywords: refraction in gas, gas heating, metal laser heating.

Experimental Estimation of the Backscatter Enhancement Peak

The intensity distribution of scattered radiation over the transmitting–receiving aperture of a turbulent lidar is experimentally studied. Sounding was performed along a horizontal path under moderate turbulence with a narrow laser beam located in the center of the receiving aperture of variable size. The relative contribution to the echo signal due to turbulence decreased as the receiving aperture increased. The BSE effect was found to be localized at the center of the receiving aperture: the peak of scattered radiation is located at the axis of the sounding beam, and its size is approximately equal to the beam size; at the periphery, the average intensity of scattered radiation slowly decreased to background values as the distance from the beam axis increased. The result can be used in practice for optimal choice of transceiver parameters when designing a turbulent lidar.

Real-time interleaved spectroscopic photoacoustic and ultrasound (PAUS) scanning with simultaneous fluence compensation and motion correction

For over two decades photoacoustic imaging has been tested clinically, but successful human trials have been limited. To enable quantitative clinical spectroscopy, the fundamental issues of wavelength-dependent fluence variations and inter-wavelength motion must be overcome. Here we propose a real-time, spectroscopic photoacoustic/ultrasound (PAUS) imaging approach using a compact, 1-kHz rate wavelength-tunable laser. Instead of illuminating tissue over a large area, the fiber-optic delivery system surrounding an US array sequentially scans a narrow laser beam, with partial PA image reconstruction for each laser pulse. The final image is then formed by coherently summing partial images. This scheme enables (i) automatic compensation for wavelength-dependent fluence variations in spectroscopic PA imaging and (ii) motion correction of spectroscopic PA frames using US speckle tracking in real-time systems. The 50-Hz video rate PAUS system is demonstrated in vivo using a murine model of labelled drug delivery.

Post-Newtonian tracking formulae to increase the shooting accuracy of autonomous LEO laser trackers

We introduce five post-Newtonian tracking formulae that would allow increasing the accuracy of the shooting systems on board autonomous LEO laser trackers. These formulae should be used when the current formulae cannot provide instants close enough to the optimal instants at which the trackers could safely shoot down unwished LEO middle-distant targets. In fact, they allow the trackers to produce not only the safest shooting actions, but also the most efficient ablations that might make the targets fall into the atmosphere for them to burn. The fact of the matter is in the falsifiability procedure introduced below, which allows to simulate sequences of unharming shooting actions with very narrow laser beams leading to identify the optimal pointing directions to previously selected debris objects whose size and composition are representative of these targets.

Adaptive Acquisition Schemes for Photon-Limited Free-Space Optical Communications

Acquisition and tracking systems form an important component of free-space optical communications due to directional nature of the optical signal. Acquisition subsystems are needed in order to search and locate the receiver terminal in an uncertainty/search region with very narrow laser beams. In this paper, we have proposed and analyzed two adaptive search schemes for acquisition systems that perform better-for the low probability of detection-than the spiral scanning approach. The first of these schemes, the adaptive spiral search, provides a better acquisition time performance by dividing the search region into a number of smaller subregions, and prioritizing search in regions of higher probability mass. The second technique-the shotgun approach-searches the region in a random manner by sampling the search region according to a Gaussian distribution. The adaptive spiral scheme outperforms the shotgun approach in terms of acquisition time, especially if the number of search subregions is large enough. However, a higher pointing accuracy is required by the adaptive spiral search in order to search the region precisely. On the other hand, the shotgun scanning approach does not require such stringent pointing accuracy.

Correction of wavelength-dependent laser fluence in swept-beam spectroscopic photoacoustic imaging with a hand-held probe

Recently, we demonstrated an integrated photoacoustic (PA) and ultrasound (PAUS) system using a kHz-rate wavelength-tunable laser and a swept-beam delivery approach. It irradiates a medium using a narrow laser beam swept at high repetition rate (∼1 kHz) over the desired imaging area, in contrast to the conventional PA approach using broad-beam illumination at a low repetition rate (10−50 Hz). Here, we present a method to correct the wavelength-dependent fluence distribution and demonstrate its performance in phantom studies using a conventional limited view/bandwidth hand-held US probe. We adopted analytic fluence models, extending diffusion theory for the case of a pencil beam obliquely incident on an optically homogenous turbid medium, and developed a robust method to estimate fluence attenuation in the medium using PA measurements acquired from multiple fiber-irradiation positions swept at a kHz rate. We conducted comprehensive simulation tests and phantom studies using well-known contrast-agents to validate the reliability of the fluence model and its spectral corrections.

Channel model and performance analysis of long-range deep sea wireless photon-counting communication

It is widely accepted that the optical signal rapidly attenuates to a level of few photons after being transmitted over several hundred meters in seawater due to the strong absorption and scattering effects. Therefore, underwater wireless optical communication based on photon-counting detectors has become a hot research topic to increase the energy efficiency and the corresponding communication range. Although there are some reports on system simulation and experimental testing, there is no comprehensive analysis of long-distance channels in the clearest deep sea waters to achieve the potential longest communication range. In this paper, a deep-sea long-range wireless photon-counting communication system is established. The blue–green narrow-beam lasers, commercial photon-counting detectors and the serially concatenated pulse position modulation are adopted. Then, aiming at the clearest deep sea optical channel, the Monte Carlo simulation method is employed and the impulse responses within 800-m are obtained. Finally, numerical results show that the delay spread is negligible in the long-distance channel and the wireless photon-counting communication performs excellently in deep sea environments. Using a 440-nm laser with an average power of 5 W and a 35-cm receiving aperture, a communication distance of 1000 m can be achieved with data rates of several tens of kbps and a bit-error-rate below 10−8.

Post-Newtonian Equations for Laser Links in Space

The purpose of this article is threefold. We first show that the second-order post-Newtonian (p-N) equations for the Earth exterior Schwarzschild field introduced in this article are the equations that, unlike those of the first p-N order, allow the space-based pointing, acquisition, and tracking laser systems to substantially reduce the size of the p-N corrections to the Newtonian location from the systems of middle size targets in orbit about the Earth. To achieve this goal the trackers must be endowed with very narrow laser beams and atomic clocks. Second, we show that these corrections can be used to speed up the trackers' shooting systems in any scenario where this kind of beam may be involved. In fact, since the first step in any procedure aimed to achieve this goal is to accurately determine the ranging and shooting directions to the targets from the lines of sight, the computation of the second p-N relative orbits of the targets with respect to the trackers must be carried out in real time. Then, the solution of these equations for the target of interest can be uploaded in the closed-loop control system on board the tracker involved, in order to initiate the control process of the respective ranging and shooting direction, as well as to reinitiate it, as soon as the target ceases to be hidden for the tracker due to the Earth. Third, we to show that these equations will be very useful for autonomous trackers to carry out two demanding tasks, namely 1) to steadily maintain intersatellite optical links and 2) to perform laser ablation of middle size LEO debris objects at operative distances.

Super-low-power optical trapping of a single nanoparticle.

We propose and demonstrate a simple approach for noncontact, three-dimensional, and stable trapping of a single nanoparticle with a super-low incident laser power (0.7mW) via the single-fiber optical tweezers. We splice a section of single-mode fiber and a section of multimode fiber to construct a Bessel-like beam, which produces narrow output laser beams. We integrate a high-refractive-index glass microsphere on the tip of the multimode fiber to focus the narrow output laser beams. The focused beams provide a nanoscale optical trap for a single nanoparticle (polystyrene sphere, diameter of 200nm). This optical fiber probe has the advantages of high laser transmission efficiency, high spatial resolution, and minimum joule heating. The proposed approach extends the application potential of fiber-based optical manipulations, such as nanoparticle sorting, single-cell organelle analysis, and bio-sensing.

IR Spectroscopy of Fullerene Ions in a Cryogenic Quadrupole Trap

Abstract This paper reports gas-phase IR spectra of (n = 1–3) ions in the range from 1100 to 1600 cm−1. The spectra were recorded with a temperature-variable radio frequency ion trap instrument. The experiments work with mass-selected ions confined in a linear wire quadrupole, where they form helium-tagged complexes following exposure to low-temperature (as low as 2.3 K) and high-density helium buffer gas. All measured lines are homogeneously broadened owing to a strong coupling between the vibrational states of the fullerene cage. The short lifetimes of picoseconds or below rule out measurements of high-resolution IR spectra. Reproducible sidebands with distances between 5 and 20 cm−1 enrich the spectra. Tentative explanations are based on nonlinear and symmetry-breaking interactions or may be due to the influence of the attached He atom. Comparison of the spectrum with that of reveals shifts up to 6 cm−1, while the IR spectra of and are very similar. With the harmonic potential of the trap the ions are squeezed into the rather narrow laser beam, increasing the sensitivity and simplifying the determination of absolute photoabsorption cross sections. Disregarding shifts of several cm−1, the gas-phase results for and are in agreement with previous matrix results and with theoretical predictions. The astrophysical relevance of our results is briefly mentioned.

Simulating the processes of radiation propagation in the receiving–transmitting tracts of laser systems

The conditions for a topological wave-front disturbance are considered in regard to narrow focused laser beams with an initially dislocation-free spatial structure. The factors affecting the accuracy of determining the phase distribution in a beam’s cross section using a shearing interferometer are considered.