Μm Radiation Research Articles

17999 Evaluation of ascorbic acid and a capsulated ascorbic acid-containing serum for protection against ambient particulate matter

Background: Air pollution causes severe damage to the skin but is less recognized in this context than UV radiation. It has been shown that particulate matter with a diameter less than 2.5 micrometers (PM2.5), a major component of air pollution, induces skin damage partially through overproduction of reactive oxygen species (ROS). Ascorbic acid (vitamin C) is a known antioxidant that may protect the skin from pollution and UV. However, ascorbic acid is easily degraded during storage. This study aimed to evaluate the efficacy of ascorbic acid and its more stable derivatives, as well as a capsulated ascorbic acid–containing serum, against PM2.5- and UV-induced ROS overproduction.

On the Transparency of Alkali-Halide Crystal in the Terahertz Spectral Range

The transmission of THz (to 3000 μm) radiation by alkali halide single crystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), and rubidium iodide (RbI), which are widely used in the IR spectral region, is studied. The spectral dependences of the absorption coefficients of these materials in the range of 0.9–3000 μm are determined. These materials are transparent in the range of 1000‒3000 μm, which makes it possible to use them in terahertz (millimeter) devices.

Measurements of nonlinear absorption of intense 10 µm laser pulses in n-Ge, GaAs, and ZnSe.

We study the nonlinear absorption of high-power 10 µm radiation propagating through n-Ge, GaAs, and ZnSe materials widely used in the long-wave infrared range. Measurements are performed using both nanosecond and picosecond CO2 laser pulses providing intensities up to 100MW/cm2 and 5GW/cm2, respectively. Nonlinear absorption coefficients in optical quality n-Ge are found to be the same for both pulse durations. The nonlinear absorption coefficient of these materials scales inverse proportionally to their bandgap energies, indicating increased photoionization in the smaller bandgap materials.

Effective nonlinearity of the new quaternary chalcogenide crystal BaGa2GeSe6.

The unknown magnitude and relative signs of the trigonal crystal ${\rm BaGa}_{2}{\rm GeSe}_{6}$BaGa2GeSe6 nonlinear coefficients have hindered defining an optimum orientation for maximum frequency conversion efficiency. This issue is resolved in the present work, obtaining ${d_{11}}= + {23.6}$d11=+23.6, ${d_{22}}= - {18.5}$d22=-18.5, and ${d_{31}}= + {18.3}\;{\rm pm/V}$d31=+18.3pm/V for frequency doubling of the 10.591 µm radiation.

Infrared Emissivity of La<sub>0.8</sub>Sr<sub>0.2</sub>MnO<sub>3</sub> under 0.76-2.5 μm and 2.5-500 μm Radiation Fields

La0.8Sr0.2MnO3 was prepared to investigate the infrared emissivity of the sample under 0.76-2.5 μm and 2.5-500 μm infrared fields. The sample exhibited characteristic peaks of rhombohedral perovskite structure at 298-318 K, and split of the main peak weakened with increasing temperature. Intensity of the ferromagnetic resonance peak enhanced with increasing temperature, and the peak was shifted toward high magnetic field. A weak paramagnetic resonance peak appeared at 318 K, indicating that ferromagnetic-paramagnetic transition was occurring. The temperature of the sample under 2.5-500 μm field was higher than that under 0.76-2.5 μm. The emissivity of the sample increased with radiation time under 2.5-500 μm, but it had no obvious changes at about 0.665 under 0.76-2.5 μm. The emissivities at the same temperature fields were higher than those under 0.76-2.5 μm and 2.5-500 μm fields, respectively. It suggested that 0.76-2.5 μm and 2.5-500 μm radiations had inhibition effect on emissivity of La0.8Sr0.2MnO3.

Infrared variability due to magnetic pressure-driven jets, dust ejection and quasi-puffed-up inner rims

ABSTRACT The interaction between a YSO stellar magnetic field and its protostellar disc can result in stellar accretional flows and outflows from the inner disc rim. Gas flows with a velocity component perpendicular to disc mid-plane subject particles to centrifugal acceleration away from the protostar, resulting in particles being catapulted across the face of the disc. The ejected material can produce a ‘dust fan’, which may be dense enough to mimic the appearance of a ‘puffed-up’ inner disc rim. We derive analytical equations for the time-dependent disc toroidal field, the disc magnetic twist, the size of the stable toroidal disc region, the jet speed, and the disc region of maximal jet flow speed. We show how the observed infrared variability of the pre-transition disc system LRLL 31 can be modelled by a dust ejecta fan from the inner-most regions of the disc whose height is partially dependent on the jet flow speed. The greater the jet flow speed, the higher is the potential dust fan scale height. An increase in mass accretion on to the star tends to increase the height and optical depth of the dust ejection fan, increasing the amount of 1–8 µm radiation. The subsequent shadow reduces the amount of light falling on the outer disc and decreases the 8–40 µm radiation. A decrease in the accretion rate reverses this scenario, thereby producing the observed ‘see-saw’ infrared variability.

A visible transparent solar infrared reflecting film with a low long-wave emittance

A dielectric/metal/dielectric (D/M/D) film with a high visible (0.38–0.78 μm) transmittance and a high solar infrared (0.78–2.5 μm) reflectance can be applied on the outdoor surface of a window for energy saving in hot weather. However, in this kind of application with a D/M/D film, the regulation of long-wave (>3 μm) radiation is often neglected but proved to be significant in energy saving according to our previous work. For a ZnO/Ag/ZnO structure on flexible PET applied as a visible transparent solar infrared reflecting film with a low long-wave emittance, based on matrix formulation and a ray-tracing method, the influence of Ag layer thickness on visible transmittance (Tvis), solar infrared reflectance (Rsi) and long-wave emittance (εlw) are investigated. Two samples with the highest Tvis and Tvis + Rsi are prepared, respectively, with high visible transmittance, high solar infrared reflectance and low long-wave emittance, simultaneously. In hot weather, compared with a traditional silica glass, the exterior applied film consumes more energy, while the interior applied film saves 9.6% energy consumption for cooling.

InGaAs avalanche photodiode thermometry

The infrared detector is the most important component within any radiation thermometry-based system, with its choice determining the wavelength, response time and, ultimately, the temperature measurement capabilities of the instrument. To improve upon the existing generation of radiation thermometers, more sensitive detector technologies are required. In this work, we demonstrate a direct comparison between an indium gallium arsenide (InGaAs) photodiode and an InGaAs avalanche photodiode (APD) for 1.6 µm radiation thermometry. The high internal gain of the InGaAs APD increases the sensitivity of the radiation thermometer, enabling the measurement of a target temperature more than 50 °C lower than is typical with commercially available InGaAs photodiode thermometers. The more sensitive InGaAs APD provides faster response time measurements, hence improving the thermometer’s temporal resolution. Finally, the InGaAs APD is shown to produce a quantitative thermal image with lower measured temperature fluctuation across the scene when incorporated within a highly aperture limited scanning system.

MEMS AlN pyroelectric infrared sensor with medium to long wave IR absorber

Polycrystalline Aluminum Nitride (AlN) thin films are of significant interest due to their pyroelectric properties for last few years. In this paper, study on development of a polycrystalline AlN thin film based bulk micromachned pyroelectric IR sensor is presented. Structural optimization of IR sensor has been carried out using 3D finite element modeling (FEM) and simulations. A 1.0 μm thick thermally grown SiO2 layer used for thermal isolation, also serves as a diaphragm to hold the fabricated IR sensor. Rate of temperature change (dT/dt) of the sensor under dynamic heating is 0.12–0.15°K/s, and agrees well with the simulated value of 0.1°K/s. High pressure, N2 ambient sputtered Au film of thickness 160 nm has been used to enhance the IR absorptivity. IR absorptivity of sensor on medium to long wave (2.5–25 μm) radiations is nearly 67%, and creates thermal gradient of 0.23°K between sensor and substrate. Developed pyroelectric IR sensor exhibits response time 8.0 ms, pyroelectric coefficient (ρ) 0.32 × 10−4 C/m2K, ρ/ε figure of merit (FOM) 3.0 μC/m2K, and pyroelectric current responsivity (Ri) of 2.5 × 10-6 A/W.

Temperature phase-matching tuning of nonlinear ZnGeP2 crystal for frequency conversion under noncritical spectral phase-matching

Temperature dependences of nonlinear ZnGeP2 crystal indices within the wavelength range of 5.0–6.2 μm (around noncritical spectral phase-matching) were examined with a frequency-selective Q-switched CO laser. The correct dependences were found and applied for numerical study of the spectrum tuning by the crystal temperature changing under the broadband CO laser sum frequency generation. The latter was experimentally studied for the crystal temperature range from the room one up to 145 °C. Requirements for ZnGeP2 crystal temperature changing needed for broadband frequency conversion of 5–7.5 μm radiation were formulated.

Laser-induced damage threshold of BaGa4Se7and BaGa2GeSe6nonlinear crystals at 1053 μm

We investigated the laser-induced damage threshold of two barium chalcogenides crystals, BaGa4Se7 and BaGa2GeSe6, at 1.053 μm radiation with a pulse duration of 7–10 ns at different pulse repetition rates, namely, 100 Hz, 500 Hz, and 1 kHz. The R-on-1 procedure was applied to determine the 0% probability damage threshold. Both crystals have close values of surface damage threshold at 0.1 kHz, 299 MW/cm2 (2.28 J/cm2) for BaGa2GeSe6, and 319 MW/cm2 (2.30 J/cm2) for BaGa4Se7.

Demonstration of distributed capacitance compensation in a metal-insulator-metal infrared rectenna incorporating a traveling-wave diode

We experimentally demonstrate that the transmission line impedance of traveling-wave diodes can circumvent resistance-capacitance time-constant limitations of metal-insulator-metal diodes in rectennas operating at optical frequencies. We fabricated low resistance (380 Ω) and moderate responsivity (0.46 A/W) metal-insulator-metal traveling-wave diodes. When a rectenna incorporating the traveling-wave diode was illuminated with 10.6 μm radiation, it produced a peak system responsivity of 130 μA/W and a detectivity of 1.0 × 104 Jones. These results agree with the simulated device performance and exceed the response of an equivalent lumped-element metal-insulator-metal rectenna.

Simultaneous detection of C<sub>2</sub>H<sub>6</sub>, CH<sub>4</sub>, and <i>δ</i><sup>13</sup>C-CH<sub>4</sub> using optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared region: towards application for dissolved gas measurements

Abstract. Simultaneous measurement of C2H6 and CH4 concentrations, and of the δ13C-CH4 isotope ratio is demonstrated using a cavity-enhanced absorption spectroscopy technique in the mid-IR region. The spectrometer is compact and has been designed for field operation. It relies on optical-feedback-assisted injection of 3.3 µm radiation from an interband cascade laser (ICL) into a V-shaped high-finesse optical cavity. A minimum absorption coefficient of 2.8×10-9 cm−1 is obtained in a single scan (0.1 s) over 0.7 cm−1. Precisions of 3 ppbv, 11 ppbv, and 0.08 ‰ for C2H6, CH4, and δ13C-CH4, respectively, are achieved after 400 s of integration time. Laboratory calibrations and tests of performance are reported here. They show the potential for the spectrometer to be embedded in a sensor probe for in situ measurements in ocean waters, which could have important applications for the understanding of the source and fate of hydrocarbons from the seabed and in the water column.

Noncooled (Hg,Cd)Te IR photo detectors in range of 10.6 μm wavelength

In range of 10.6 μm IR radiation an analysis of noncooled (T = 300 K) (PC) photodiodes and (EMCD) magnetoexlusion detectors with (Hg,Cd)Te was made. The basic detection parameters of these devices are limited by the noise resulting from statistical processes of thermal generation and carrier recombination. The parameter evaluation of related photodiodes demonstrates that the optimal parameters such as: thickness or structure doping on the substrate with a widened energy gap differs each other for structures with ohmic contacts at both ends. In the paper, for photodiodes and magnetoexclusion detectors with (Hg,Cd)Te the research results : optimal photosensitive detection parameters are presented for the room temperature (T=300 K) and acceptable large as well as small (5 and 0.5 W / mm2) densities of the dissipated power.

Enhancement of substrate-coating adherence of boron-doped diamond electrodes by nanosecond laser surface texturing pretreatment

To improve the substrate-coating adherence of Nb-based boron-doped diamond (BDD) electrodes, laser surface texturing (LST) pretreatment was investigated. Substrates were textured by a Nd:YAG laser (1.06 μm radiation, 20 ns) with several laser parameters such as single pulse energy and scanning spacing, then coated with a BDD film by hot filament chemical vapor deposition (HFCVD). Characteristics of the substrates and BDD thin film electrodes were investigated. The results revealed that periodic valley-like structures were fabricated on substrate surfaces. LST pretreatment can significantly enhance the substrate-coating adherence of BDD electrode samples, and the laser cleaning step can effectively remove the surface oxide layer generated by laser pretreatment. Single pulse energy is a crucial influencing factor, the proper pulse energy can provide the best adherence property, providing sufficient surface treatment effect, promoting nucleation, release residual stress and promote the mechanical interlock. Suitable scanning spacing can further improve the coating adherence, and the match of scanning spacing and single pulse spacing can effectively avoid the directional peeling.

Generation of 2 μm radiation due to single-mode fibers with longitudinally varying diameter

Abstract We report on numerical modeling of the spectral dynamics of telecom range laser pulse of moderate power in a silica fiber with a flattened dispersion and longitudinally varying diameter. In the simulation experiments, the optimal fiber profile has been proposed for more than 60% energy transfer from the initial telecom range pulse to subpicosecond pulse at 2.2–2.3 μm. Another option of the fiber diameter profile provides flat radiation spectrum in the range 2–2.5 μm.

Laser-induced heating for enhanced fatigue life of aerospace aluminum alloys

According to airworthiness requirements, the primary structure of a commercial aircraft must be designed to be damage tolerant in order to guarantee the aircraft structural integrity. For this reason, the crack propagation analysis of metallic materials is performed during the structural design development. It is known that compressive residual stresses enhance the performance of structural components by retarding the crack propagation rate, extending the fatigue life of such components. For this reason, aircraft manufacturers may apply some process like mechanical peening, ball-burnishing and laser shock peening to improve the fatigue life of structural parts. This contribution aims to propose the laser surface treatment of aerospace aluminum alloys as a possible way to reduce the crack propagation rate in compact tension C(T) coupons. Since the laser technology has been already used in welding and cutting operations, the same setup could be used to produce discrete heating lines with low cost. Three types of aluminum alloys were analyzed Al–Zn–Mg–Cu (AA7475-T761), pure aluminum-coated Al–Cu (AA2024-T3) and Al–Si–Mn–Cu–Mg (AA6013-T4), for better understanding of phenomena related to the crack propagation. A carbon coating was proved to allow good absorptivity of the laser beam, since the aluminum surface is highly reflective to the fiber laser 1 µm radiation. It was verified that two laser tracks, with power 200 W, speed below 5 mm/s and beam diameter of about 2 mm, consistently results in a crack-retardant piece. According to the actual results, the laser processing barely doubled the fatigue life under some conditions. The main mechanism of crack retardation had been associated with the modification of stresses ahead of the crack tip, since the microstructure and hardness were almost unchanged after the laser treatment. The maximum measured compressive stresses ahead of the laser track for AA7475-T761, AA2024-T3 and AA6013-T4 were 30, 30 and 67 MPa, respectively.

Structural, spectral, thermal, and optical studies of stilbazolium derivative crystal: (E)-4-(3-hydroxy-4-methoxystyryl)-1-methyl pyridinium iodide monohydrate

In the current research, (E)-4-(3-hydroxy-4-methoxystyryl)-1-methyl pyridinium iodide monohydrate (HMSI) has been prepared through Knoevenagel condensation and crystallized by slow evaporation technique. Crystallographic analysis has been carried out to study the crystal structure and unit cell parameters. The fundamental vibration frequencies of specific chemical functional groups were detected by infrared absorption spectrum. Further the molecular structure of the grown crystal was confirmed by nuclear magnetic resonance spectroscopic analysis. Thermal stability (145 °C) and meting point (248 °C) of the HMSI material have been elaborated by means of thermogravimetric and differential scanning calorimetric (TG/DSC) analysis. The crystal was found to be transparent above 460 nm with the band gap of 2.63 eV obtained from transmission spectral analysis. The growth features of HMSI crystal were examined to check for the defects using an optical microscope. Crystal surface damage by Nd: YAG laser at 1.064 μm radiation was measured to be 1.98 GW/cm2. Further, the nonlinear response of HMSI has been studied using Z-scan technique and it was found that the title crystal is capable of exhibiting self-focusing nature with reverse saturable absorption. The evaluated nonlinear susceptibility is in the order of 10−6 esu which is slightly higher compared to other third-order stilbazolium derivative crystals.

Hot carrier impact on photovoltage formation in solar cells

The photovoltaic effect in a GaAs p-n junction exposed to short laser pulses of the 1.06–3.0 μm spectral range is investigated experimentally. At a low excitation level of 1.06 μm radiation, the intraband single photon absorption of light dominates, and the photoresponse is found to be caused mainly by the hot carriers. As the laser intensity is increased, the photoresponse signal across the junction consists of two components; the hot carrier photovoltage and the classical photovoltage due to electron-hole pair generation resulting from two-photon absorption. The generation-induced photovoltage decreases with the increase in the radiation wavelength following the reduction of the two-photon absorption coefficient, while the carriers are shown to be heated by the intraband light absorption as well as by residual photon energy left over during the electron-hole pair generation. It is established that carrier heating by light reduces conversion efficiency of a solar cell not only via the thermalization process but also due to the competition of the hot carrier and the classical photovoltages which are of opposite polarities.

Combined effects of resveratrol and radiation in GH3 and TtT/GF pituitary adenoma cells.

Resveratrol and radiation decrease viability in various tumor cells. This study aims to investigate combined effects of resveratrol and radiation on viability, induction of apoptosis and necrosis, and expression of apoptosis modulators in rodent GH3 and TtT/GF pituitary adenoma cells in vitro. Cells were incubated with 10-100µM resveratrol. Medium and medium with ethanol served as controls. After 2h, cells were irradiated with 0-5 Gray (Gy) and further incubated for 48-72h. Cell viability was quantified using a hemocytometer. Cell death was assessed with an enzyme-linked immunosorbent assay (ELISA) that detects free nucleosomes in cell lysates and free nucleosomes released to the culture medium. Expression of B-cell lymphoma-2 protein (BCL-2) and BCL-2 associated Xprotein (BAX) was measured using quantitative real time-polymerase chain reaction (qRT-PCR) to analyze changes in BAX/BCL-2 ratio. Resveratrol and irradiation with 4 Gy alone and in combination significantly decreased cell viability (p = 0.017 and less). In the ELISA, 10 μM resveratrol significantly induced apoptosis in TtT/GF cells at 0 Gy (p < 0.001), but not at 3 or 5 Gy. In the ELISA, 10 μM resveratrol significantly induced necrosis in GH3 cells at 0, 3 and 5 Gy (p < 0.001). While qRT-PCR did not demonstrate a significant effect of 10 µM resveratrol or radiation on expression of BAX or BCL-2, a significant increase in the BAX/BCL-2 ratio was found after irradiation with 5 Gy in GH3 cells (p = 0.0027). While moderate irradiation solely led to inhibited proliferation, resveratrol induced cell death in rodent pituitary adenoma cells.