Vacuum ultraviolet gain measurements in optically pumped LiYF4:Nd3+

 We present measurements of the net-induced gain on the 5d–4f transition at 186 nm in LiYF₄ : Nd³⁺ optically pumped by radiation from a molecular fluorine laser. It is found that for LiYF₄ : Nd³⁺, one of a series of potential continuously tunable VUV lasers, relatively strong excited-state absorption results in net-induced loss. The prospects for VUV laser operation being realised in other rare-earth-doped fluorides is discussed. Received: 4 March 1996/Revised version: 10 July 1996     

Regression approach to non-invasive determination of bilirubin in neonatal blood

A statistical ensemble of structural and biophysical parameters of neonatal skin was modeled based on experimental data. Diffuse scattering coefficients of the skin in the visible and infrared regions were calculated by applying a Monte-Carlo method to each realization of the ensemble. The potential accuracy of recovering the bilirubin concentration in dermis (which correlates closely with that in blood) was estimated from spatially resolved spectrometric measurements of diffuse scattering. The possibility to determine noninvasively the bilirubin concentration was shown by measurements of diffuse scattering at λ = 460, 500, and 660 nm at three source–detector separations under conditions of total variability of the skin biophysical parameters.     

Wavelength Dependant Quenching of 2,5-Diphenyloxazole Fluorescence by Nucleotides

The quenching of 2,5-diphenyloxazole (PPO) fluorescence by nucleotides has been investigated by electronic absorption and steady state fluorescence spectra. Five purine nucleotides AMP, ADP, ATP, GMP and dGMP, one pyrimidine nucleotide UMP and one dinucleotide NAD have been employed in the present study. Electronic absorption studies indicate that there is no ground state complexation between the nucleotides and PPO. The quenching of PPO fluorescence was investigated at two different wavelengths. When excited at 304 nm, the λ _max of PPO, the fluorescence spectra of PPO is quenched following Stern–Volmer kinetics. The quenching ability of nucleotides are in the order NAD > AMP > ADP > GMP > dGMP > UMP. The K _SV and k _q values obtained indicate that AMP is a better quencher of PPO fluorescence than GMP, which is contrary to commonly observed pattern. The quenching is found to be dynamic in nature. However, when excited at 260 nm, the absorption maximum of the nucleotides, the fluorescence intensity of PPO is reduced with increase in the concentration of the nucleotide. This is attributed to the primary inner filter effect arising due to the absorption of the incident radiation by the nucleotides. Thus the inner filter effect phenomenon can be employed to assay the non-fluorescent molecules by fluorimetry.     

Optical characterization of sol gel TiO<Subscript>2</Subscript> monoliths doped with Brilliant Green

Amorphous titanium dioxide monoliths doped with brilliant green (BG) were synthesized by the sol-gel process. The optical properties of the monoliths were characterized by Photoacoustic Spectroscopy and Photoluminescence Spectroscopy. The absorption spectra for the BG-doped TiO₂ monoliths exhibited two well defined absorption regions: a band below 400 nm corresponding to TiO₂ absorption and three absorption bands centered at 424 nm, 588 nm, and 632 nm due to brilliant green. While the undoped TiO₂ monoliths showed no luminescence, the doped samples showed a strong luminescence band at 673 nm, which increased its intensity for increasing organic dye doping.     

Luminescence investigations of the degradation of 2-methylphenol and 4-methylphenol in water

Fluorescent characteristics of the photo- and biotransformations of 2-methylphenol, 4-methylphenol and their mixtures in water exposed to uv radiation of various sources and to Penicillium tardum H-2 culture have been studied. The toxicity of these solutions has also been investigated by means of bioluminescent testing. Preliminary exposure of a 4-methylphenol solution (10⁻³ M) to uv radiation with λ ∼ 308 nm or to the radiation of a mercury lamp inhibited the subsequent microbiological degradation. Efficient decomposition of methylphenol molecules in the mixture was detected when it was exposed to the radiation of a mercury lamp or to 222-nm radiation and then subject to biodecomposition. The irradiation of solutions of 2-methylphenol and 4-methylphenol and their low-concentration mixtures with 308-nm uv radiation or with the radiation of a mercury lamp resulted in detoxication of the solutions. Extreme toxicity was shown by 4-methylphenol solutions on exposure to uv radiation with λ ∼ 222 nm. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 88–98, December, 2008.     

An off-axis cavity-enhanced absorption spectrometer at 1605 nm for the 12CO2/13CO2 measurement

A distributed feedback diode laser sensor based upon off-axis cavity-enhanced absorption spectroscopy at 1605.5 nm has been developed for ¹³C¹⁶O₂/¹²C¹⁶O₂ isotope ratio measurements in synthetic air and human breath. A noise-equivalent absorption sensitivity of 3.9×10^-10 cm^-1 Hz^-1/2 has been determined for a cavity base length of 28.2 cm and averaging 4000 scans within 8.688 s. For 5% CO₂ concentration measurements, δ¹³C standard deviations of 1.8 ‰ and 3.7 ‰ have been estimated for five successive measurements based on peak height and integrated area estimations at 107.9 Torr, respectively. The contributions of amplified spontaneous emission of the laser and a radiation that is spatially uncoupled into the cavity mode have been described for cavity transmittance measurements. The limitations of the developed sensor and further steps towards precision and accuracy improvements are discussed. PACS 42.55.Px; 39.30.+w; 42.62.Fi; 42.60.-v     

Nonlinear absorption properties correlated with the surface and structural changes of ultra short pulse laser irradiated CR-39

We have investigated femtosecond laser irradiation effects on the surface topography, structural changes and nonlinear absorption properties of CR-39. For this purpose, a CR-39 target was exposed in air to 25 fs, 800 nm Ti: sapphire laser radiation at fluences ranging from 0.25 J cm⁻² to 3.6 J cm⁻². The surface of irradiated CR-39 probed by an Atomic Force Microscope (AFM) exhibits the formation of several topographical structures, like bumps, explosions and nano cavities. Raman spectroscopy is performed to explore chemical and structural modification of the irradiated target. The spectroscopy reveals changes such as cross linking, bond breaking, formation of new bonds etc. in the fundamental structure of the polymer after irradiation. In order to establish a correlation between morphological and structural changes with the changes in the nonlinear absorption of the irradiated CR-39, a Z-scan technique was employed. A comparison of experimentally obtained data from Z-scan measurements with our calculations predicts the dominance of three-photon absorption in the case of pristine CR-39, whereas for irradiated targets concurrence of three- and two-photon absorption is probable. Nonlinear absorption increases with increasing laser fluences and is well correlated by surface and structural changes revealed by AFM and Raman spectroscopy.     

Photoacoustic spectroscopy of Baru – <Emphasis Type="Italic">Dipteryx alata</Emphasis> Vog

Photoacoustic spectroscopy (PAS) was used to investigate samples produced from Baru (Dipteryx alata Vog.), a typical fruit from the Brazilian Cerrado, which is considered as a good source of nutrients. The photoacoustic (PA) spectra of samples prepared from Baru seeds present three different absorption bands in the wavelength range 0.3–1.0 μm, named Band-C, Band-S, and Band-L. We found that PAS can be useful for monitoring the strong absorption of visible light by Baru's seeds constituents mainly in the shorter wavelength measured range. This study is important from both agricultural and commercial point of view once it introduces PAS as a potential characterization technique allowing better control of fruit and seed selection, storage and transportation.     

The carotenoid content in seedlings of maize seeds irradiated by a 650 nm diode laser: Qualitative photoacoustic study

The aim of the present study was to obtain qualitative content of carotenoids in the leaves of maize seedlings the seeds of which were irradiated by the 650 nm diode laser. Four different irradiation doses have been applied; and the control (non-irradiated) seeds used for comparison purposes. Optical absorption spectra of leaves from seedlings were recorded by means of photoacoustic spectroscopy in the 400 to 500 nm range. The experimental unit comprised 10 seeds, among which one seedling was selected at random for each repetition. Data was subjected to variance analysis (ANOVA) using the SAS GLM procedures (SAS, 1998 version). The ANOVA revealed significant (p < 0.05) differences among treatments in the 471 to 478 nm range.     

Degradation and protection of polyaniline from exposure to ultraviolet radiation

The effect of UV radiation on both pure and additive-containing polyaniline thin films is described. Experimental investigations included optical transmittance spectroscopy and electrical conductivity measurements. Exposure to UV radiation in the range of 380 to 400 nm was seen to increase film transmittance by 4% through photobleaching. Different gas ambients were employed for this experiment and progressively more photobleaching was observed for nitrogen, air and oxygen atmospheres. This effect arises due to the destruction of quinoid and benzenoid chromophores on the polymer backbone. Concomitantly, a decrease in film resistivity was also observed and this can be attributed to increased oxidative doping of the film material. The addition of controlled amounts of Tinuvin 213—an ultraviolet absorber (UVA) material—was seen to reduce the UV-induced degradation of polyaniline thin films by absorption of UV photons through regenerative intramolecular photolysis.     

Optical Properties of Zinc Oxide Nano-particles Embedded in Dielectric Medium for UV region: Numerical Simulation

Zinc oxide nano-particles have been used by cosmetic industry for many years because they are extensively used as agents to attenuate (absorb and/or scatter) the ultraviolet radiation. In the most UV-attenuating agent is formulated in which the metal oxide nano-particles are incorporated into liquid media or polymer media are manufactured, such as sunscreens and skin care cosmetics. In this paper we study the wavelength dependence on the particle size (r _eff = 10–100 nm) by solving the scattering problem of hexagonal ZnO particle for different shapes (plate, equal ratio, column) using the discrete dipole approximation method to find the absorption, scattering, and extinction efficiencies for the UV region (30–400 nm). A new modified hexagonal shape is introduced to determine the scattering problem and it is assumed in this study that the wavelength is comparable to the particle size. From these results, we conclude that the optimum particle radius to block the UV radiation is between r _eff = 40–80 nm.     

ps-laser scribing of CIGS films at different wavelengths

Continuous growth of the thin-film electronics market stimulates the development of versatile technologies for large-scale patterning of thin-film materials on rigid and flexible substrates, and laser technologies are a promising method to accomplish the scribing processes. Lasers with picosecond pulse duration were applied in scribing of complex multilayered CuIn _x Ga_(1−x)Se₂ (CIGS) solar cells deposited on a polyimide substrate. The ablative properties of the films were examined as a function of the wavelength of laser radiation, pulse energy, and the irradiation dose. The selective removal of ITO and CIGS layers was achieved with 355 nm irradiation without any significant damage to the underlying layers in the ITO/CIGS/Mo/PI solar cell system. The 355 nm wavelength was also found to be favorable for scribing of absorber layer in a ZnO/CIGS/Mo/PI solar cell system. 266 nm radiation significantly modified the film structure due to high absorption. Extensive melt formation in the CIGS layer was found when 532 nm radiation was applied, though the trenches were smooth and crack-free.     

Atomic force microscopy, Raman spectroscopy and nonlinear absorption properties of femtosecond laser irradiated CR-39

Investigations have been performed to explore ultrashort laser irradiation effects on the surface topography as well as structural and nonlinear absorption properties of a polymer CR-39. For this purpose, a CR-39 target was exposed in air to 25 fs, 800 nm Ti:sapphire laser radiation at fluences ranging from 0.25 J cm⁻² to 3.6 J cm⁻². The surface features, structural changes and nonlinear absorption were explored by AFM, Raman Spectroscopy and a Z-scan technique, respectively. Several topographical structures like bumps, explosions and nano cavities have been observed on the irradiated surface. Raman spectroscopy reveals changes in the fundamental structure of the polymer after the irradiation. Nonlinear absorption data contained by the Z-scan technique predict the dominance of three-photon absorption in case of pristine CR-39. Furthermore, nonlinear absorption (three or two photon) increases with increasing laser fluences and is well correlated with surface and structural changes revealed by AFM and Raman spectroscopy.     

Mid-infrared generation and spectroscopy with a PPLN ridge waveguide

We have utilised a periodically poled LiNbO₃ crystal with a waveguide structure to produce up to 146 μW of mid-IR radiation around 2976 cm^-1 by difference frequency mixing of 1064 nm pump radiation with 1558 nm signal radiation. A conversion efficiency of 45% W^-1 is achieved within a crystal of length 50 mm, and temperature tuning curves are reported. The resultant idler radiation is exploited for high resolution absorption studies of both methane and methanethiol. The absorption cross-sections for methanethiol in the region of 2979 cm^-1 are measured and found to be ∼10^-19 cm², the relevance of these results to breath and headspace analysis of clinical samples containing volatile sulphur compounds is briefly discussed. PACS 42.62.Fi; 42.65.Ky     

Photoacoustic Spectroscopy to determine <Emphasis Type="Italic">in vitro</Emphasis> the non radiative relaxation time of protoporphyrin IX solution containing gold metallic nanoparticles

In order to compare the non radiative relaxation time (NRRT) between standard protoporphyrin IX (PpIX) and protoporphyrin PpIX(1) solution containing gold metallic nanoparticles, we measured the photoacoustic spectroscopy (PAS) signal phase to determine, for each solution, the NRRT by using the Rosencwaig-Gesho theory, modified to include the effect of a finite non radiative deexcitation time. A NRRT average value, obtained for each solution, is reported and compared with some NRRT of triplet states reported in the literature for molecules with the same tetrapyrrolic structure. In the study was used PpIX disodium salt (DS) solution of 25% HCL. From each solution it was obtained its optical absorption spectrum, by using a UV-Vis spectrophotometer. After this, in the maximum observed optical absorption peak (404 nm), it was obtained the Photoacoustic (PA) signal phase as a function of the light modulation frequency, from 17 to 80 Hz. Our investigations are devoted to the improvement of the thermal treatments of drugs for medical applications.     

On the effect of ultraviolet radiation on water vapor absorption of submillimeter waves

The submillimeter absorption spectra of pure water vapor and a water vapor + dry air mixture are experimentally studied under the conditions of illumination of the gas sample by ultraviolet (UV) radiation. The measurements were carried out by a vacuum echelette spectrometer in the wave number range 21.5–56 cm⁻¹ with spectral resolution 0.4–0.9 cm⁻¹, using a DRT-375 mercury-vapor discharge lamp as the source of UV radiation. In contrast to the results of similar experiments performed by other researchers, the data presented here demonstrate the absence of a noticeable effect of the UV radiation on the absorption spectra of the gas samples used. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 581–587, May, 1998.     

High resolution ethylene absorption spectrum between 6035 and 6210 cm-1

A two-channel photo-acoustic spectrometer (PA spectrometer) with a near infrared diode laser was used for taking measurements of a high resolution ethylene absorption spectrum. A semiconductor TEC-100 laser with an outer resonator generates a continuous single-frequency radiation in the range 6030–6300 cm^-1. A newly designed model of photo-acoustic detector (PAD) in the form of a ring type resonator provides for measurement of weak absorption cross-section equal to 4×10^-23 cm²/mol at a laser radiation power of 3 mW. The PAD threshold sensitivity is 2×10^-9 cm^-1 Hz^-1/2 W, when the signal to noise ratio equals to 1. The ethylene absorption spectrum within the range 6035–6210 cm^-1 was measured for the first time with a spectral resolution of 10 MHz. The reported line centre positions have an uncertainty of ± 0.0005 cm^-1. The precise measurements of ethylene absorption cross-sections were carried out using the mixture of high purity ethylene and broadening gas (nitrogen) at the mixture ratio 1:50–1:200. Measurements were carried out at a mixture pressure of about 4.2 kPa. PACS 42.62.Fi; 42.55.Px     

Wavelength modulation and cavity enhanced absorption spectroscopy using ～1.9?μm radiation produced by difference frequency generation with a MgO doped PPLN crystal

We have demonstrated the production of ∼1.9 μm near-infrared radiation by using difference frequency generation within a 5% MgO doped PPLN crystal by coupling ∼735 nm radiation from a tunable external cavity diode laser with relatively high powered 532 nm radiation from both Nd:YVO₃ and Nd:YAG lasers. The radiation produced is of low power, ∼15 μW, and was used in conjunction with the sensitivity enhancing techniques of wavelength modulation spectroscopy (WMS) and cavity enhanced absorption spectroscopy (CEAS). Experiments were carried out on rotationally resolved transitions in the combination bands of NH₃ and CO₂ in the 1.9 μm region. An α _min value of 3.6×10⁻⁶ cm⁻¹ Hz^−1/2 was achieved for WMS measurements on CO₂. A comparable α _min value of 2.2×10⁻⁶ cm⁻¹ Hz^−1/2 was achieved for NH₃ using CEAS. The low NIR power indicates that despite the level of MgO doping quoted for the crystal, under prolonged exposure photorefractive damage has occurred.     

Thermal effects on optical properties of silver ruby glass

2 O·10 CaO·74 SiO₂ mol%) glass doped with 0.11 and 0.35 wt.% silver are investigated. Heating treatments are carried out in a temperature range between 400 and 575 °C for times ranging from 30 to 300 min in different atmospheres and cooling rates. The starting glasses show a colourless and transparent appearance, but after thermal treatments under a reducing atmosphere become coloured, confirming the presence of silver colloids related to the 410-nm absorption band. On the other hand, the main effects of thermal treatments on the PL spectra concern those from samples treated in a reducing atmosphere. Thus, the intensity of both excitation and emission spectra chiefly diminishes in the 220–230 nm and 325–350 nm ranges, respectively. In addition, time-resolved spectra show the main ultraviolet (UV) emission centred above 330 nm upon excitation with 228-nm light. In contrast to the starting glass, we notice no shift or even slight shifts of the peak position to longer wavelengths with increasing delay time after pulse excitation, even for delay times as short as 0.01 ms. The results are discussed on the basis of transitions in which Ag⁺ ions are involved. Received: 6 February 1998/Accepted: 9 March 1998     

The structure,composition, and dimensions of TiO<Subscript>2</Subscript> and ZnO nanomaterials in commercial sunscreens

TiO₂ and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO₂ and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO₂ pigments were generally rutile nanocrystals (dimensions ~25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO₂ and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.