Thermal Lens Technique as a Potential Optical Tool

The spectroscopic characterization of materials involves the use of various optical tools. Spectrometers, interferometers etc, are some of the examples of optical tools. Thermal lens technique is one of the potential optical tools for the thermal characterization of different materials. The thermal lens effect is a photothermal effect which results when energy from a laser beam is absorbed by a sample, causing heating of the sample along the beam path. In this paper an overview of thermal lensing, its significance as potential optical tool and its applications are discussed. Index Terms: Optical tool, Photothermal spectroscopy, TLS application, Thermal diffusivity

Advances in anthropomorphic thorax phantoms for radiotherapy: a review

A phantom is a highly specialized device, which mimic human body, or a part of it. There are three categories of phantoms: physical phantoms, physiological phantoms, and computational phantoms. The phantoms have been utilized in medical imaging and radiotherapy for numerous applications. In radiotherapy, the phantoms may be used for various applications such as quality assurance (QA), dosimetry, end-to-end testing, etc. In thoracic radiotherapy, unique QA problems including tumor motion, thorax deformation, and heterogeneities in the beam path have complicated the delivery of dose to both tumor and organ at risks (OARs). Also, respiratory motion is a major challenge in radiotherapy of thoracic malignancies, which can be resulted in the discrepancies between the planned and delivered doses to cancerous tissue. Hence, the overall treatment procedure needs to be verified. Anthropomorphic thorax phantoms, which are made of human tissue-mimicking materials, can be utilized to obtain the ground truth to validate these processes. Accordingly, research into new anthropomorphic thorax phantoms has accelerated. Therefore, the review is intended to summarize the current status of the commercially available and in-house-built anthropomorphic physical/physiological thorax phantoms in radiotherapy. The main focus is on anthropomorphic, deformable thorax motion phantoms. This review also discusses the applications of three-dimensional (3D) printing technology for the fabrication of thorax phantoms.

Functional Photonic Elements Based on Liquid Crystal Metasurfaces

We study versatile soft-matter metasurfaces based on self-assembling of nematic liquid crystal on polymer alignment layers processed with a focused ion beam. Digital control of the beam path allows imprinting patterns that induce different complex distributions of the refractive index within several micrometer thick liquid crystal layers. We optimize them to implement various optical functionalities, such as broadband anomalous refraction, wide-aperture focusing, and beam splitting in tens of channels.

Analysis of chromatic aberrations influence on operation of the tunable AOTF-based source

Developing a source with the possibility of tuning in wavelengths based on an acousto-optical tunable filter (AOTF), an essential factor is the ability to provide accurate color coordinates of the simulated color (in the case of developing a color standard for colorimetry) or the required wavelength (in the case of an application for spectral studies). As shown earlier, the choice of the principal layout – confocal or parallel beam path - primarily determines the dimensions and efficiency of using the luminous flux. However, these schemes also need to be analyzed for color or wavelength fidelity, considering other components used in the scheme. The analysis performed allows to identify the optimal scheme to ensure the required color reproduction accuracy and establish the requirements for correcting chromatic aberrations of the components.

Development of custom lead shield and strainer for targeted irradiation for mice in the gamma cell chamber

We presented a development of a custom lead shield and mouse strainer for targeted irradiation from the gamma-cell chamber. This study was divided into two parts i.e., to (i) fabricate the shield and strainer from a lead (Pb) and (ii) optimize the irradiation to the mice-bearing tumour model with 2 and 8 Gy absorbed doses. The lead shielding was fabricated into a cuboid shape with a canal on the top and a hole on the vertical side for the beam path. Respective deliveries doses of 28 and 75 Gy from gamma-cell were used to achieve 2 and 8 Gy absorbed doses at the tumour sites.

Biological and Mechanical Synergies to Deal With Proton Therapy Pitfalls: Minibeams, FLASH, Arcs, and Gantryless Rooms

Proton therapy has advantages and pitfalls comparing with photon therapy in radiation therapy. Among the limitations of protons in clinical practice we can selectively mention: uncertainties in range, lateral penumbra, deposition of higher LET outside the target, entrance dose, dose in the beam path, dose constraints in critical organs close to the target volume, organ movements and cost. In this review, we combine proposals under study to mitigate those pitfalls by using individually or in combination: (a) biological approaches of beam management in time (very high dose rate “FLASH” irradiations in the order of 100 Gy/s) and (b) modulation in space (a combination of mini-beams of millimetric extent), together with mechanical approaches such as (c) rotational techniques (optimized in partial arcs) and, in an effort to reduce cost, (d) gantry-less delivery systems. In some cases, these proposals are synergic (e.g., FLASH and minibeams), in others they are hardly compatible (mini-beam and rotation). Fixed lines have been used in pioneer centers, or for specific indications (ophthalmic, radiosurgery,…), they logically evolved to isocentric gantries. The present proposals to produce fixed lines are somewhat controversial. Rotational techniques, minibeams and FLASH in proton therapy are making their way, with an increasing degree of complexity in these three approaches, but with a high interest in the basic science and clinical communities. All of them must be proven in clinical applications.

Оптимизация масс-сепараторов

The optimization of separator masses in this paper is based on the realization of the linearity of the system under study and the consequences of Liouville's theorem. The properties of several mass separators with an ion energy of 30 keV and a beam emittance of 4 mm*mrad are considered. Focusing is provided by an aberration-free lens and a magnetic corrector. Phase diagrams along the beam path are in the form of parallelograms, which indicates the absence of geometric aberrations. For each of the separators, the resolution calculated in the linear approximation coincides with the simulation results. It is shown that a mass separator based on a magnet with a rotation angle of 54.70 has a resolution of about 5000, and a separator based on two magnets with a rotation angle of 450 and 900, respectively, has a resolution of 14000-15000.

Interpretation of weak backscattering signals in a weakly clouded atmosphere

It is used here the lidar equation describing signals from a weakly turbid atmosphere to solve the problem of the determination of the atmospheric aerosol parameters. It is worthwhile to note that the backscattering and extinction coefficients are constant along the beam path in this case. First approximation of the exponent process can be used to describe the atmospheric extinction. The weak lidar signals were analyzed here. It is useful for calculations of the extinction coefficient the preliminary known value of this parameter. The systematic errors were analyzed for different points along the beam path. The signal power was measured at sufficiently large distance. The systematic errors of the extinction coefficient can exceed the systematic errors of the backscattering signal power. It was shown that corresponding value achieve 20. There was investigated the influence of the systematic errors of the measured signal including background light on the obtained results. It was shown that the obtained results cannot be accurate enough if we use preliminary obtained data found before the measurement. It is found that the relative error of the measured signal ˂1%. It is very important the relative error of the corresponding extinction coefficient can be ˃ 100%. There were investigated the results of measurements and the results of computations. First of all it is associated with the scattered irradiance. The cases were considered with absence and presence of water in the aerosol particles coating. It was shown that the developed models adequately describe the process of scattering by a particle. So it is possible significantly reduce the aerosol sizing error. This model can be applied in determining the pollution of the Arctic air basin.

Fabrication and characterisation of a silicon-borosilicate glass microfluidic device for synchrotron-based hard X-ray spectroscopy studies

Left – A schematic view of the XAS microfluidic set up at the beamline; fluorescence detector at 90° angle to the X-ray beam (green line); right – microfluidic device setup on Balder beamline mounted perpendicular to beam path.