Beam Quality Research Articles

High power and excellent beam quality rod Yb: YAG regenerative amplifier

High power and excellent beam quality rod Yb: YAG regenerative amplifier

Efficient fiber coupling system for simultaneous beam shaping and wavelength combining based on misaligned stepped prism multiplexing

Due to the substantial contrast in the output beam quality between the two directions of the semiconductor laser, efficiently coupling the beam directly into the fiber is difficult. In this study, an efficient shaping method based on step multiplexing of misaligned step prisms is proposed and investigated systematically. First, multiple laser stacks eliminate dark areas to improve the beam quality through the full utilization of the transmission and reflection surfaces of the misaligned stepped prisms, which also improves the efficiency of the stepped prisms. It also simultaneously realizes laser wavelength combining based on reflective surface multiplexing without affecting the quality of the beam on the premise of improving the output power. Finally, the whole beam shaping system is completed without using cut-transform-rearranging prisms. The method couples four groups of laser stacks into a single fiber with a fiber diameter of 400 µm and a numerical aperture of 0.22. It can be seen from the computer-simulated model outputs that the final fiber output power can reach 2255.4 W and that the system as a whole has a light-to-light translation rate of 88.1%.

Simultaneous polarization and wavelength merging for efficient fiber coupling system using a designed one-mirror prism

The difference in beam quality between the fast-axis and slow-axis directions of semiconductor lasers limits its wide application. Conventional development methods for solving this problem require a large number of optical components. A one-mirror prism shaping scheme based on wavelength combination and polarization combination techniques is proposed to simultaneously halve the optical width in the slow-axis direction and fill in the dark region in the fast-axis direction to improve and equalize the beam quality. Compared with the traditional beam shaping scheme, the design does not use the cutting-translation-rearrangement of prism technology to avoid uneven spot distribution at the same time, the use of the design of a single prism can achieve several functions to improve the efficiency of prism utilization, to avoid the use of prism stacks, the whole system is simple and compact, easy to implement The design couples two laser stacks, both consisting of 10 cm-bars, into the target fiber with a fiber characteristic of 400 μm, 0.22. An output power of 1415.8 W is obtained from the output end of the fiber, and the coupling efficiency is calculated to be 88.5%.

SiN‐On‐SOI Optical Phased Array LiDAR for Ultra‐Wide Field of View and 4D Sensing

Abstract3D imaging techniques are facilitating autonomous vehicles to build intelligent systems. Optical phased arrays (OPAs) featured by all solid‐state configurations are becoming a promising solution for 3D imaging. However, the majority of state‐of‐art OPAs commonly suffer from severe power degradation at the edge of the field of view (FoV), resulting in limited effective FoV and deteriorating 3D imaging quality. Here, the chained grating antenna and the vernier concept is synergized to design a novel OPA for realizing a record wide 160°‐FoV 3D imaging. By virtue of the chained antenna, the OPA exhibits less than 3‐dB beam power variation within the 160°FoV. In addition, two OPAs with different pitches are integrated monolithically to form a quasi‐coaxial Vernier OPA transceiver. With the aid of a flat beam power profile provided by the chained antennas, the OPA exhibits uniform beam quality at an arbitrary steering angle. The superior beam steering performance enables the OPA to accomplish 160° wide‐FoV 3D imaging based on the frequency‐modulated continuous‐wave (FMCW) LiDAR scheme. The ranging accuracy is 5.5‐mm. Moreover, the OPA is also applied to velocity measurement for 4D sensing. To the best of knowledge, it is the first experimental implementation of a Vernier OPA LiDAR on 3D imaging to achieve a remarkable FoV.

Experimental comparison of cylindrical and plane parallel ionization chambers for reference dosimetry in continuous and pulsed scanned proton beams

Objective. In this experimental work we compared the determination of absorbed dose to water using four ionization chambers (ICs), a PTW-34045 Advanced Markus, a PTW-34001 Roos, an IBA-PPC05 and a PTW-30012 Farmer, irradiated under the same conditions in one continuous- and in two pulsed-scanned proton beams. Approach. The ICs were positioned at 2 cm depth in a water phantom in four square-field single-energy scanned-proton beams with nominal energies between 80 and 220 MeV and in the middle of 10 × 10 × 10 cm3 dose cubes centered at 10 cm or 12.5 cm depth in water. The water-equivalent thickness (WET) of the entrance window and the effective point of measurement was considered when positioning the plane parallel (PP) ICs and the cylindrical ICs, respectively. To reduce uncertainties, all ICs were calibrated at the same primary standards laboratory. We used the beam quality (k Q ) correction factors for the ICs under investigation from IAEA TRS-398, the newly calculated Monte Carlo (MC) values and the anticipated IAEA TRS-398 updated recommendations. Main results. Dose differences among the four ICs ranged between 1.5% and 3.7% using both the TRS-398 and the newly recommended k Q values. The spread among the chambers is reduced with the newly k Q values. The largest differences were observed between the rest of the ICs and the IBA-PPC05 IC, obtaining lower dose with the IBA-PPC05. Significance. We provide experimental data comparing different types of chambers in different proton beam qualities. The observed dose differences between the ICs appear to be related to inconsistencies in the determination of the k Q values. For PP ICs, MC studies account for the physical thickness of the entrance window rather than the WET. The additional energy loss that the wall material invokes is not negligible for the IBA-PPC05 and might partially explain the low k Q values determined for this IC. To resolve this inconsistency and to benchmark MC values, k Q values measured using calorimetry are needed.

Characterization of selected additive manufacturing materials for synchrotron monochromatic imaging and broad-beam radiotherapy at the Australian synchrotron- imaging and medical beamline.

This study aims to characterize radiological properties of selected additive manufacturing (AM) materials utilizing both material extrusion and vat photopolymerization technologies. Monochromatic synchrotron X-ray images and synchrotron treatment beam dosimetry were acquired at the hutch 3B of the Australian synchrotron - imaging and medical beamline (AS-IMBL).
Approach: Eight energies from 30 keV up to 65 keV were used to acquire the attenuation coefficients of the AM materials. Comparison of theoretical, and experimental attenuation data of AM materials and standard solid water for MV linac was performed. Broad-beam dosimetry experiment through attenuated dose measurement and a Geant4 Monte Carlo simulation were done for the studied materials to investigate its attenuation properties specific for a 4 tesla wiggler field with varying synchrotron radiation beam qualities.
Main results: PLA plus matches attenuation coefficients of both soft tissue and brain tissue, while ABS, ASA, and Draft resin have close equivalence to adipose tissue. Lastly, PLA, CPE plus, TPU, and White resins are promising substitute materials for breast tissue. For broad-beam experiment and simulation, many of the studied materials were able to simulate RMI457 SolidWater and bolus within +/-10% for the three synchrotron beam qualities. These results are useful in fabricating phantoms for synchrotron and other related medical radiation applications such as orthovoltage treatments. 
Significance and conclusion: These 3D printing materials were studied as potential substitutes for selected tissues such as breast tissue, adipose tissue, soft-tissue, and brain tissue useful in fabricating 3D printed phantoms for synchrotron imaging, therapy, and orthovoltage applications. Fabricating customizable heterogeneous anthropomorphic phantoms (e.g. breast, head, thorax) and pre-clinical animal phantoms (e.g. rodents, canine) for synchrotron imaging and radiotherapy using AM can be done based on the results of this study.

High energy and high repetition rate QCW-LD end-pumped electro-optical Q-switched Yb:YAG laser

The quasi-continuous wave laser diode (QCW-LD) pumping is considered as the most efficient way for generating high energy nanosecond pulsed laser with repetition rate ranging from 50 to 1000 Hz. Here, a high efficiency, high repetition rate and high energy QCW-LD end-pumped electro-optical (EO) Q-switched Yb:YAG laser was demonstrated. The shortest pulse duration of 17.4 ns with a maximum single pulse energy of 5.1 mJ was obtained at the repetition rate of 100 Hz. As the repetition rate increases up to 500 Hz, the maximum output single pulse energy was obtained to be 5.38 mJ with the pulse width of 18.7 ns, corresponding to the slope efficiency of 21.6% and beam quality factor of M x 2=1.04, and M y 2=1.01. In addition, a theoretical study was carried by numerical simulation of the rate equations, and the results were agreed well with the experimental ones. The results show that QCW-LD pumping with Yb-doped crystals is a promising way for highly efficient, high-energy and high repetition rate nanosecond pulsed laser generation.

Stereotactic body radiation therapy (SBRT) for prostate cancer: Improving treatment delivery efficiency and accuracy

PurposeIn stereotactic body radiation therapy (SBRT) for prostate cancer, intrafraction motion is an important source of treatment uncertainty as it could not be completely smoothed through fractionation. Herein, we compared different arrangements and beam qualities for extreme hypofractionated treatments to minimize beam delivery time and so intrafractional errors. MethodsA retrospective dataset of 11 patients was used. Three volumetric modulated arc therapy (VMAT) beam arrangements were compared for a prescription dose of 40 Gy/5 fractions: two full arcs, 6 MV flattening filter free (FFF); one full arc, 6 MV FFF; one full arc, 10 MV FFF. A plan quality index was defined to compare achievement of the planning goals. Plan complexity was evaluated with the modulation factor. Dose delivery accuracy and efficiency were measured with patient-specific quality assurance plans. ResultsAll treatment plans fulfilled all dose objectives. No statistical differences were found both in plan quality and complexity. Very accurate dose delivery was achieved with the three arrangements, with mean γ passing rates >96.5 % (2 %/2 mm criteria). Slightly but significantly higher γ passing rates were observed with single-arc 6 MV FFF. Contrariwise, statistically significant reductions of the delivery time were obtained with single-arc geometries: the average delivery times were 1.6 min (−46.1 %) and 1.3 min (−56.2 %) for 6 and 10 MV FFF respectively. ConclusionsThe high-quality, very fast and accurate dose delivery of single-arc plans confirmed the suitability of this arrangement for prostate SBRT. In particular, the significant reduction of delivery time would improve treatment robustness against intrafraction prostate motion.

High efficiency continuous-wave Ho: LSO laser wing-pumped by the laser diode at 1.91 μm

We present a high-efficiency continuous-wave Ho: LSO laser wing-pumped by a 1.91 μm laser diode. The impact of different output transmittances on the laser output power is compared and analyzed. The optimal result was achieved with a −500-mm radius curvature and a 6% transmission output coupler. The maximum output power of the Ho: LSO laser is 7.81 W, with a slope efficiency of 44.7%, a center wavelength of 2,106.6 nm, and beam quality factors of 1.4 in the x-direction and 1.3 in the y-direction.

Beam quality conversion factor of BeO-OSLD for high-energy photon beams

Optically stimulated luminescence (OSL) dosimeters are used in radiotherapy. The beam quality conversion factor () of dosimeters is essential for correcting energy dependence. However, the of an OSL dosimeter using BeO (BeO-OSLD) has not yet been reported for high-energy photon beams. In this study, the of BeO-OSLD was investigated for high-energy photon beams using experiments and Monte Carlo calculations. In the experiments, was evaluated as the ratio of calibration coefficients determined using high-energy photon beams and 60Co γ-rays. Ten OSL dosimeters were used to reduce the statistical uncertainty of the determined values, and the same dosimeters were repeatedly used to obtain the data set of high-energy photon beams and 60Co γ-rays. Pre-irradiation with 10 Gy and bleaching were performed on fresh dosimeters before dosimetry to reduce the dependence of the detector response on the accumulated dose. In Monte Carlo calculations, both the absorbed dose to water and that of the BeO dosimeter for high-energy photon beams and 60Co γ-rays were calculated, and then was determined using the ratio of these values. The determined values in high-energy photon beam were 0.998 ± 0.011 and 1.021 ± 0.005 for the experiment and the calculation, respectively. These results showed that the variation in for 6 to 25 MV was negligible in practical dosimetry. This result indicates that BeO can be used to evaluate doses for different beam qualities without correcting for energy dependence.

Ultra-highly sensitive dual gases detection based on photoacoustic spectroscopy by exploiting a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser.

Photoacoustic spectroscopy (PAS) as a highly sensitive and selective trace gas detection technique has extremely broad application in many fields. However, the laser sources currently used in PAS limit the sensing performance. Compared to diode laser and quantum cascade laser, the solid-state laser has the merits of high optical power, excellent beam quality, and wide tuning range. Here we present a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser used as light source in a PAS sensor for trace gas detection. The self-built solid-state laser had an emission wavelength of ~2 μm with Tm:YAP crystal as the gain material, with an excellent wavelength and optical power stability as well as a high beam quality. The wide wavelength tuning range of 9.44 nm covers the absorption spectra of water and ammonia, with a maximum optical power of ~130 mW, allowing dual gas detection with a single laser source. The solid-state laser was used as light source in three different photoacoustic detection techniques: standard PAS with microphone, and external- and intra-cavity quartz-enhanced photoacoustic spectroscopy (QEPAS), proving that solid-state laser is an attractive excitation source in photoacoustic spectroscopy.

Adjoint Algorithm Design of Selective Mode Reflecting Metastructure for BAL Applications.

Broad-area lasers (BALs) have found applications in a variety of crucial fields on account of their high output power and high energy transfer efficiency. However, they suffer from poor spatial beam quality due to multi-mode behavior along the waveguide transverse direction. In this paper, we propose a novel metasurface waveguide structure acting as a transverse mode selective back-reflector for BALs. In order to effectively inverse design such a structure, a digital adjoint algorithm is introduced to adapt the considerably large design area and the high degree of freedom. As a proof of the concept, a device structure with a design area of 40 × 20 μm2 is investigated. The simulation results exhibit high fundamental mode reflection (above 90%), while higher-order transverse mode reflections are suppressed below 0.2%. This is, to our knowledge, the largest device structure designed based on the inverse method. We exploited such a device and the method and further investigated the device's robustness and feasibility of the inverse method. The results are elaborately discussed.

Growth, thermal, spectroscopy and ∼2.7 μm multiwavelength laser output of Er:GYAP crystal

We demonstrate the growth, thermal, spectroscopy and laser performance of a Er3+ doped Gd0.1Y0.9AlO3 (Er:GYAP) disorder crystal grown by Czochralski method. The crystal with space group Pbnm and lattice parameters of =0.5185 nm, =0.5327 nm, =0.7378 nm, α=β=γ=90° and =0.203784 nm3 are obtained by fitting powder X-ray diffraction data. The Mohr’s hardnesses along three axes are 6.94, 7.27, and 7.44. The thermal expansion coefficient of axis is 4.20 × 10–6 K–1 and the density is 5.88 g/cm3. The thermal conductivities are characterized as =6.24, =5.57, and =6.83 W/(m·K). Meanwhile, the refractive index, absorption and emission spectra in triaxial directions are determined. Besides, level lifetimes of 4I11/2 and 4I13/2 are 0.86 and 2.83 ms. Finally, the ∼2.7 μm multiwavelength laser outputs are observed with maximum average power of 628 mW and beam quality factors / of 1.42/1.45. The results prove that the Er:GYAP crystal is a promising gain medium for generating mid-infrared lasers.

Effect of Spherical Aberration of Lens and Laser Intensity Distribution on Beam Quality

Effect of Spherical Aberration of Lens and Laser Intensity Distribution on Beam Quality

Simulation Method for the Impact of Atmospheric Wind Speed on Optical Signals in Satellite–Ground Laser Communication Links

To analyze the intensity of atmospheric turbulence in a satellite–ground laser communication link, it is important to consider the effect of increased atmospheric turbulence caused by wind speed. Atmospheric turbulence causes a change in the refractive index, which negatively impacts the quality and focusing ability of the laser beam by altering its phase front. To simulate the changes in amplitude and phase characteristics of laser beam propagation in atmospheric turbulence caused by wind speed, a transverse translation phase screen is used. To better understand and address the influence of atmospheric wind speed on the phase of optical signals in satellite–ground laser communication links, this paper proposes a Monte Carlo simulation method. This method utilizes the spatial and temporal variations in the refractive index in the atmosphere and integrates the principles of optical signal propagation in the atmosphere to simulate changes in the phase of optical signals under different wind speed conditions. By analyzing the variations in the received optical signal’s power, the Monte Carlo method is employed to simulate phase screens and logarithmic amplitude screens. Additionally, it models the probability density of the statistical behavior of received optical signal’s fluctuations, as well as the time autocorrelation coefficient of optical signals. This paper, under the coupling condition in satellite–ground laser communication links, conducted a Monte Carlo simulation experiment to analyze the characteristics of the optical signal’s fluctuations in the link and discovered that atmospheric wind speed affects the shape of the power spectral density model of the received optical signal. Increasing wind speed leads to a decrease in the time autocorrelation coefficient of the received optical signal and affects the coupling efficiency. The paper then used a cubic spline interpolation fitting method to verify the models of the power spectral density and the autocorrelation time coefficient of the optical signal. This provides a theoretical foundation and practical guidance for the optimization of satellite–ground laser communication systems.

High beam quality continuous-wave 320 nm UV laser from walk-off compensated intracavity frequencydoubled Pr:YLF laser

High beam quality continuous-wave 320 nm UV laser from walk-off compensated intracavity frequencydoubled Pr:YLF laser

Improved relative gain in Nd3+doped GeO2-PbO glass with double waveguides irradiated by femtosecond laser micromachining and decorated with Au nanoparticles

The paper explores the effects of Au nanoparticle (NP) islands deposited by sputtering technique on the surface of Nd3+-doped GeO2-PbO glasses, with double-line waveguides, produced via femtosecond laser processing for photonics. A Ti:sapphire femtosecond laser operating at 800 nm was employed to inscribe the waveguides directly into the glass, 0.7 mm beneath the surface. These waveguides were structured as pairs of parallel lines separated 10 μm. Additional procedures were undertaken to position the waveguides on the glass surface where Au NPs were deposited. Refractive index change of 10−3 at 632 nm was observed in both horizontal and vertical directions. Similar results for the beam quality factors (Mx2 and My2) at 632 nm and 1064 nm indicated x, y-symmetrical guiding. Photoluminescence and relative gain growth were observed due to Au NP islands. The relative gain reached 3.0 dB/cm representing an increase of approximately 450 % when compared to samples without the Au NP islands, and was attributed to the local field growth in their vicinities. This study highlights the potential to change Nd3+-doped GeO2-PbO glasses optical properties with Au nanoparticle islands, opening up new and promising prospects for photonics and 1064 nm optical amplifiers.

Minimum phantom size for megavoltage photon beam reference dosimetry.

Water phantoms are required to perform reference dosimetry and beam quality measurements but there are no published studies about the size requirements for suchphantoms. To investigate, using Monte Carlo techniques, the size requirements for water phantoms used in reference dosimetry and/or to measure the beam quality specifiers and . The EGSnrc application DOSXYZnrc is used to calculate , the dose per incident fluence at 10cm depth in a water phantom irradiated by incident beams of or 6MV photons. The water phantom dimensions are varied from to and occasionally smaller. The and values are also calculated with care being taken to distinguish results when using Method A (changing depth of water in phantom) and Method B (moving entire phantom). Typical statistical uncertainties are 0.03%. Phantom dimensions have only minor effects for phantoms larger than . A table of corrections to the dose at 10cm depth in beams of or 6MV photons are provided and range from no correction to 0.75% for a beam incident on a phantom. There can be distinct differences in the values measured using Method A or Method B, especially for smaller phantoms. It is explicitly demonstrated that, within 0.15%, values for a phantom measured using Method A or B are independent of source detector distance between 40 and200cm. The phantom sizes recommended in the TG-51 and IAEA TRS-398 reference dosimetry protocols are adequate for accurate reference dosimetry and in some cases are even conservative. Correction factors are necessary for accurate measurement of the dose at 10cm depth in smaller phantoms and these factors are provided. Very accurate beam quality specifiers are not required for reference dosimetry itself, but for specifying beam stability and characteristics it is important to specify phantom sizes and also the method used for measurements.

The design and optimization methods towards 10 kW high beam quality fiber laser based on counter tandem pumping scheme

The design and optimization methods towards 10 kW high beam quality fiber laser based on counter tandem pumping scheme

OSLD nanoDot characterization for carbon radiotherapy dosimetry.

This study characterized OSLD nanoDots for use in a therapeutic carbon beam using the IROC framework for remote output verification. 
Approach: The absorbed dose correction factors for OSLD (fading, linearity, beam quality, angularity, and depletion), as defined by AAPM TG 191, were characterized for carbon beams. For the various correction factors, the effect of carbon LET was examined by characterizing in both a low and high LET setting. 
Main Results: Fading was not statistically different between reference photons and carbon, nor between low and high LET carbon; thus, the standard IROC-defined exponential function could be used to characterize fading. Dose linearity was characterized with a linear fit; while low and high LET carbon linearity was different, these differences were small and could be rolled into the uncertainty budget if using a single linearity correction. A linear fit between beam quality and dose-averaged LET was determined. The OSLD response at various angles of incidence was not statistically different, thus a correction factor need not be applied. There was a difference in depletion between low and high LET carbon irradiations, but this difference was small over the standard five readings. The largest uncertainty associated with the use of OSLDs in carbon was because of the kQ, with an uncertainty of 6.0%. The overall uncertainty budget was 6.3% for standard irradiation conditions. 
Significance: OSLD nanoDot response was characterized in a therapeutic carbon beam. The uncertainty was larger than for traditional photon applications. These findings enable the use of OSLDs for carbon absorbed dose measurements, but with less accuracy than conventional OSLD audit programs.&#xD.