Optical Bleaching Research Articles

Investigation of the Photobleaching Process of Eosin Y in Aqueous Solution by Thermal Lens Spectroscopy

Eosin Y is known to be a powerful probe of biological molecules and an efficient photosensitizing agent for the production of singlet molecular oxygen. Under continuous laser excitation, degradation through photobleaching is observed in aqueous solutions of eosin Y; this process is driven by the production of singlet oxygen. Optical bleaching in aqueous solutions is known to yield anomalous thermal lens transient signals, which can be evaluated by modeling the relaxation processes that give rise to the generation of heat in the solution. A model describing photobleaching in the thermal lens transient signal is derived and is applied to investigate eosin Y in aqueous solutions at different temperatures. Using this model, quantitative information regarding the molecular diffusion rate, optical bleaching, and fluorescence quantum efficiency is obtained.

Effects of antifreezes and bundled material on the stability and optical limiting in aqueous suspensions of carbon nanotubes

AbstractThis work gives data on the stability of dispersions of single wall carbon nanotubes stabilized by sodium dodecylbenzenesulfonate in binary polar solvents “water + antifreeze” (glycerol, polyethyleneglycole) with eutectic compositions. The absorption spectra of the suspensions demonstrate no changes during 1‐year storage with temperature spanning from −40 to +40 °C. The systems provide relevant optical power limiting properties, the one with glycerol showing good resistance to optical bleaching effects. We also demonstrate that aqueous dispersions of nanotubes exhibit considerable enhancement of optical limiting parameters alongside an increase of the bundled material populace.

Photothermal Spectrometry in Small Liquid Channels

A novel apparatus for performing photothermal lens spectroscopy is described. The apparatus uses a low-volume cylindrical sample cell, a chopped or pulsed excitation laser, and a continuous probe laser. The full volume of the sample is irradiated with constant, e.g., non-Gaussian, irradiance beam produced by the excitation laser. Constant irradiance excitation source does not directly produce the photothermal lens element in the sample. The lens element is formed by thermal diffusion from the irradiated sample volume, through the sample cell walls. Under continuous irradiation, thermal diffusion results in a parabolic temperature change profile. The apparatus has been found to work with cells designed to contain sample volumes from 6 μL down to 24 nL. Larger and smaller volume cells are practical but signals produced in the smallest sample cells exhibit deviation from that expected based on the theory. This is attributed to probe laser diffraction by the circular aperture of the sample cell. (Received on August 9, 2001, Accepted on......) Introduction Photothermal lens spectrometry is a novel means to measure optical absorption. It is one of several ultra-sensitive photothermal spectroscopy methods applicable to trace analysis. The applicability to trace analysis is due to the high sensitivity and small sample volumes needed for an analysis. There are several physical effects that limit sensitivity and influence the accuracy of measurements obtained using photothermal lens spectrometry. First, the photothermal lens signal is related to the lens formed the sample as a consequence of light absorption and subsequent energy transfer to the matrix. The optical element produced when laser beams are focussed into a homogeneous sample is not a simple lens. The aberrant nature of the photothermal lens results in signal magnitudes that are somewhat smaller than expected and also more difficult relate to sample absorbance. Second, sample irradiation can produce large temperature changes. In theory, the on-axis temperature change approaches infinity at long times for any excitation power when using continuous laser excitation sources. In practice, large temperature changes distort the thermal lens perturbation due to density differences and convection heat transfer or even boiling may occur. The later distorts the signal and ruins the analytical utility. Other factors resulting in inaccurate absorbance determination are related to the photophysics of sample excitation and solvent (matrix) relaxation. Nonlinear optical absorption and bleaching, transient volume changes, and excited state analyte absorbance can occur when using high irradiance laser excitation sources. These effects may generally be avoided only by using low irradiance. This is often accomplished by choosing continuous over pulsed lasers for sample excitation. An apparatus utilizing a two-laser photothermal lens apparatus that is immune to many problems associated with photothermal lens spectrometry and capable measuring optical absorbance in very small samples is described in this work. The apparatus uses a nanoliter-volume sample cell with a visible laser used as the excitation source. The sample cell is constructed from high thermal conductivity metal and has a large surface area and relatively large heat capacity. A simplified version of the theory for describing the photothermal lens developed in a cylindrical sample cell is given. A model for relating signals to sample absorbance is given and experimental evidence is presented. Timedependent photothermal signals are detected The technique exhibits high sensitivity and can be used for ultra-sensitive detection. Analyte excitation is often performed using laser light sources. The resulting photothermal lens is measured using a probe laser. Excitation and probe lasers may be the same. Laser light sources produce a small spot size at a focus. The small spot size allows one to probe extremely small sample volumes. Theory Theoretical time-dependent temperature changes and inverse photothermal lens focal lengths for both standard and cylindrical sample cells are described in the literature. The cylindrical sample cell used here has a large thermal conductivity compared to the solvent. Little temperature change occurs at the sample cell wall because of the high thermal conductivity ratio. The solution to the thermal diffusion equation for a zero temperature change at the cell wall temperature change is

Modelling the optical bleaching of the thermoluminescence of K2YF5:Pr3+

Abstract Optical bleaching of the thermoluminescence (TL) curve of K 2 YF 5 :Pr 3+ has been observed after optically stimulated luminescence (OSL) readout of pre-irradiated crystals. The traps being responsible for the TL signal are not emptied completely by the optical stimulation. Furthermore, if the illumination time is increased a constant intensity level of the residual TL glow curve is eventually achieved. On the other hand, if the low temperature peak of the glow curve is thermally cleaned, no subsequent OSL is measured. This behavior has been successfully explained by assuming that part of the electrons in the trap being responsible for the low temperature glow peak of K 2 YF 5 :Pr 3+ recombine with holes via localized transitions during optical stimulation. During TL all trapped electrons recombine via delocalized transitions. Simulations have been carried out in order to demonstrate the feasibility of the model.

Optical bleaching and radiation response of feldspar TL glow peaks separated by using computerized glow curve deconvolution

The thermoluminescence (TL) peaks of feldspar were separated using the computerized glow curve deconvolution (CGCD) method combined with the second-derivative technique and were investigated not only for bleaching with different light sources (blue and infrared) but also for luminescence response to radiation dose. In the results, the TL glow peak was separated into four peaks at 280 °C, 315 °C, 360 °C, and 440 °C. Each separated TL glow peak exhibited two exponential decays in the signal bleached using blue or infrared stimulation. In view of all four separated glow peaks, the bleaching of the first (second) exponential component was faster (slower) for both the blue and the infrared stimulation as the peak temperature increased, and the bleaching of the first (second) exponential component with blue stimulation was faster (slower) than that with infrared stimulation. In addition, we found that with added beta dose, the shapes of the growth curves showed no substantial differences for the separated glow peaks.

SU-E-T-69: A Novel Method Using Agfa-Kodak- Computer Radiography System for Routine Quality Assurance Tests on Linear Accelerators

Purpose: Since conventional radiographic films are becoming obsolete, we have developed a novel technique utilizing Computer Radiography (CR) plates to perform routine Linac quality assurance checks. Methods: A photostimulable CR plate can detect both direct and indirect ionization radiation, and is even sensitive to photons in the visible range. A technique involving optical bleaching of radiation field on CR plate is being established as the calibration tool for performing routine quality checks such as: light field radiation congruence, symmetric/asymmetric jaw positioning. The CR plate is removed from its cassette with minimal background light and is exposed to a known field size of 6/18 MV photons in air at a fixedsource to surface distance. The jaws are then moved in to form a smaller field size, and light field is then shone on the pre exposed plate. This causes photo bleaching of radiation field proportional to the jaw settings and thereby providing a suitable surrogate to establish the light and radiation coincidence. The plate is then read utilizing a Kodak (ACR 2000i) scanner which reads the photo stimulated luminescence and converts the signal into a digital image pixel map. Analysis using a MATLAB-based algorithm was done to compute the dose gradient at the junction of the light and radiation field. The technique has been tested against conventional methods of usingfilm and graph paper. Results: All light and radiation field measurements using the CR plate were within 1 mm from measurements. The method has been verified for its reproducibility and estimated uncertainty involving software based analysis has been found to be within +/− 0.2%. Conclusions: A method to efficiently, accurately and reproducibly perform routine QA has been developed. The technique has yielded a reproducible method to quantify the congruence between the light and the radiation field.

Efficient Synthesis of 6-Hydroxy-6-Aryloxymethyl-1,5-Diaryl-1,3,5-Triazinane-2,4-Dithiones

An efficient and convenient method for the synthesis of 6-hydroxy-6-aryloxymethyl-1,5-diaryl-1,3,5-triazinane-2,4-dithiones via condensation of 2 equiv. of 1-arylthioureas with aryloxyacetic acids using ferric chloride hexahydrate as catalyst is described. Triazine derivatives have important medicinal properties, are widely used in the textile, plastic and rubber industries, and have applications as pesticides, dyestuffs, optical bleaches, explosives and surface active agents.

The relation between optical bleaching and sedimentological features of fluvial deposits in the Toruń Basin (Poland)

Distributions of equivalent doses ( D E ) obtained by the Single Aliquot Regenerative-dose (SAR) OSL method applied for large aliquots of coarse quartz grains extracted from fluvial sediments are presented and analysed with respect to a fluvial palaeoenvironment. The Nowe Dąbie and Łochowo fluvial succession from the western part of Toruń Basin (eastern part of Noteć–Warta streamway, Toruń-Eberswalde ice-marginal valley) was analysed. The fluvial depositional conditions controlling the extent of daylight bleaching are reconstructed by sedimentological studies. The relation between the amount of bleaching and sedimentological properties of fluvial deposits indicate that ripple cross-laminated sands that accumulated on the floodplain and horizontally-bedded sands deposited in shallow channels are more appropriate for OSL dating than sands derived from the deep channel. Along with luminescence results obtained for the river deposits, data measured from an ancient pottery sample, ensuring complete reset of the OSL signal, are presented, compared to and discussed. On this base the poorly bleached sediment samples are identified and an adjustment factor is introduced for correcting their OSL dating results in order to avoid age inversion. The application of the adjustment factor is found to minimize overestimation of OSL ages of sediments. &nbsp

Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

Abstract Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ∼140 and ∼330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL225 °C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL50 °C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.

Investigation of nitrogen plasma effect on the nonlinear optical properties of PMMA

Effects of low power direct current nitrogen plasma on linear and nonlinear optical properties of red BS dye-doped poly(methyl methacrylate) (PMMA) film are studied employing different optical techniques. From spectrometry data, it is shown that applying plasma in such a low range of power does not affect the linear absorption coefficient, linear refractive index, and optical bandgap of this dye-doped polymer; however, nonlinear parameters are changed. Experiments are performed using the second harmonic of a continuous Nd-Yag laser beam at a 532-nm wavelength and 20-mW power. The effect of nonlinear refractive index of red BS dye-doped PMMA film in broadening the laser beam is observed. The optical bleaching behavior is investigated by measurement of the intensity of laser beam through the sample. Its third-order nonlinearity is measured using close and open Z-scan data. Nonlinear absorption coefficient and refractive index, as well as real and imaginary parts of the third-order nonlinear optical susceptibility χ 3 , are changed significantly due to plasma treatment.

Giant photoinduced optical bleaching at room and liquid helium temperatures in Sb/As 2S 3 multilayered films

We report the observation of giant photo induced optical bleaching in Sb/As 2S 3 multilayered film at room and liquid He temperatures, when irradiated with 532 nm laser at moderate intensities. The experimental results show a dramatic increase in transmittance near the band gap regime at both the temperatures; however the rates at which transmission change occurs are rather slow at low temperature. The huge change in transmission is due to the photo induced intermixing of As 2S 3 layer with Sb. Our XPS measurements show that photo induced intermixing occurs through the wrong homopolar bonds, which under actinic light illumination are converted into energetically favored hetropolar bonds.

Recovering laboratory doses using fine-grained quartz from Chinese loess

Abstract Here we report the results of dose recovery experiments carried out on fine-grained quartz from a Holocene sample in Chinese loess. Optical bleaching prior to giving a 9.35 Gy dose in the laboratory was carried out using artificial light sources, namely blue light emitting diodes (LEDs) and a solar simulator, followed by more than 24 h storage at room temperature. Stimulating the quartz with blue LEDs at room temperature resulted in overestimation of the recovered dose, whereas using the same stimulation time at temperatures above 150 °C resulted in the correct value for the recovered dose. Exposure to the solar simulator for times less than 200 min resulted in overestimation of the dose, whereas progressive underestimation was found for longer bleaching times. When doses of up 5333 Gy were given ahead of a 200 min exposure to the solar simulator, the dose recovered depended upon the magnitude of the previous dose, thus questioning the general application of a simple dose recovery experiment.

Source-trap characterization of thermally transferred OSL in quartz

Thermally transferred optically stimulated luminescence (TT-OSL) of quartz is the low intensity OSL measured after heating a previously optically zeroed quartz to temperatures below that erasing the OSL electron trap. We identify the source traps contributing to TT-OSL by studying the changes in TT-OSL and thermoluminescence (TL) caused by optical bleaching at various temperatures and by repeated TT-OSL measurements, and quantify source-trap parameters using the Hoogenstraaten method. We find that both the single transfer mechanism and the double transfer mechanism are contributing to TT-OSL production. Three source traps are identified when the samples are heated to 300 °C for 10 s to induce the thermal transfer. The first one corresponds to a TL peak at ∼200 °C. It captures electrons during the optical bleaching and releases these charges during subsequent heating. It provides ∼10% of the electrons that give rise to TT-OSL. The second trap corresponds to a TL peak at 290–300 °C and provides ∼80% of the electrons for TT-OSL through the single transfer mechanism. This electron trap has a depth of 1.34 ± 0.05 eV and a frequency factor in the order of 1011 s−1. It has a mean lifetime of 0.24 Ma at 10 °C. The third trap corresponds to a TL peak at ∼380 °C and provides ∼10% electrons for TT-OSL through the single transfer mechanism. It has a depth of 1.66 ± 0.07 eV and a frequency factor in the order of 1012 s−1. To validate the techniques used we also determined the parameters of the fast component OSL trap and received results consistent with published values. Most importantly, our results show that the relatively short lifetime of the main TT-OSL source trap limits possibilities of using TT-OSL to extend the age range of quartz OSL dating, as has been suggested by various authors.

SU‐E‐T‐229: Clinical Implementation and Validation of Optically Stimulated Luminescence Dosimeters (OSLDs) for Radiotherapy Dosimetry

Purpose: To experimentally validate and clinically implement a new OSLDs system containing Al2O3: C for measuring skin dose for the patients undergoing radiotherapy treatment. Methods and materials: The calibration measurements of the commercially available OSLDs were performed in a solid water phantom using therapeutic photon and electron beams. All measurements were carried out in a standard clinical set‐up using 100 cm SSD, 10 ×10 cm2 field size, and dmax depth for each photon and electron beam energies. In total, 100 OSLDs were irradiated with the same dose. Inter‐OSLD response variation was calculated by taking the difference between the average value and each OSLD response. A simple optical bleaching system was applied for the OSLDs using a regular fluorescent light. The accuracy of the OSLD measurement was assess by comparing with the expected ion chamber reading and MOSFET measurements carried out under the identical condition in patients. Results: In the phantom study, the overall inter‐OSLD response variations were 2.8% and 6.4% for 10 MV photon and 10MeV e‐beam, respectively. OSLD response variation between the different energies was clinically insignificant. Optical bleaching took less than 2 hours while using fluorescent light with residual signal of less than 0.3%. For the patient study, the OSLDs reading were comparable to MOSFET measurement. Summary and Discussion: Our preliminary results using OSLDs show good agreement with clinically used MOSFET measurement in patients. Screening of general purpose OSLDs is highly recommended before using in patient. The OSLDs are accurate, can be readout/use multiple times, single readout does not anneal the chip, and more importantly it is convenient to put in the patientˈs body. Further validation and clinical implementation of OSLDs for all therapeutic‐beams as well as on‐board‐imaging system will be advantageous for more accurate clinical dosimetry for advanced radiotherapy procedures such as SBRT, IGRT.

LiMgPO 4:Tb,B OSL phosphor – CW and LM OSL studies

In the adjoining paper, the authors have proposed LiMgPO 4:Tb,B (LMP) OSL phosphor as a potential alternative to α-Al 2O 3:C for dosimetry applications. This calls for developing an understanding on TL and OSL aspects of this highly sensitive LMP phosphor. CW and LM OSL processes were therefore studied experimentally and kinetic analysis was carried out using theoretical models. Continuous wave (CW) OSL curve for LMP phosphor was found not to follow single decaying exponential implying that the CWOSL curve does not follow first order kinetics. Under pre-readout annealing at 125, 200 and 300 °C for 10 s, the nature of decay profile was unaffected and same holds true for optically bleached CWOSL curves. From linearly modulated (LM) OSL studies, it was found that the shape/geometrical factor μ g was ∼0.72 ± 0.03 for wide range of doses (up to 12 Gy studied) and peak position “ t m ” was also independent of dose. The μ g was found to be unaffected with pre-readout annealing at 125, 200 and 300 °C for 10 s and optical bleaching, however it was found that peak position “ t m ” shifted towards higher side in time with increase of optical bleaching. Dose dependence tests were also carried out for LMOSL curves and it was found that peak position “ t m ” was independent of dose, which is typical characteristic of curves following first order kinetics. Hence LM-OSL curve might be mixture of more than one component. Further from CW and LM OSL studies, it was also found that the individual contribution from first, second and third TL peak toward OSL is ∼33%, ∼45% and ∼22%, respectively. Traps beyond 350 °C were found not to contribute towards OSL when stimulated using blue LEDs. In the present paper, the CW and LM OSL processes for LMP phosphor were studied experimentally and their kinetic analysis was carried out.

UV-induced bleaching of deep traps in Harshaw TLD LiF:Mg,Cu,P and LiF:Mg,Ti

The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P and LiF:Mg,Ti materials were investigated. During a normal heating cycle, LiF:Mg,Cu,P is limited to a maximum temperature of 240 °C. LiF:Mg,Ti can be read to higher temperatures; however, encapsulation in polytetrafluoroethylene limits the maximum readout temperature to 300 °C. Generally, for both materials, these respective temperatures are sufficient for emptying traps corresponding to the main dosemetric peaks. However, when the dosemeters are subjected to a high dose level, such as 1 Gy (much higher than individual monitoring dose levels), higher temperature traps are filled that cannot be emptied without exceeding the above-mentioned maximum temperatures. These high temperature traps tend to be unstable during normal readout and can significantly increase the residual TL signal. The purpose of this study was to investigate the applicability of a UV-induced bleaching technique for emptying higher temperature traps following high-dose applications. In addition, in the case of LiF:Mg,Cu,P, where the maximum readout temperature is significantly lower, we investigated the possibility of reducing the residual signal using the application of repeated readout cycles. The optical bleaching approach was found to be effective in the case of LiF:Mg,Ti; however, for LiF:Mg,Cu,P, no reduction in the residual signal was observed. For this latter material, the application of repeatable readout cycles is very effective and residual signals equivalent to dose levels as low as 0.01 mGy were observed following an initial dose of 5 Gy. To the best of our knowledge, this work is the first attempt to apply an 'optical annealing' technique to the Harshaw thermoluminescent dosemeter (TLD) materials.

Dating mortar by optically stimulated luminescence: A feasibility study

Quartz is the datable component in mortar. Although its luminescence properties are very well studied, the problem of mortar dating arises from a low level of optical bleaching. In order to reduce the time consuming efforts for dating lime mortar in monuments by optically stimulated luminescence, we investigated the most suitable methods of dose and dose rate determination, and we explored tests which are suitable to predict the datability of a given material. Reverting to the large number of publications on sedimentary partially bleached quartz we found linear modulation techniques especially useful, equally we also recommend the determination of the level of optical depletion before starting analyses. Single grain analysis is regarded as an ultimate but infallible tool to date very poorly bleached quartz from mortar. Dose rate measurements need to take into account the radioactive equilibrium of the uranium decay and the short range inhomogeneity of the environmental gamma radiation field: gamma spectrometry and on-site TLD measurements are best suited.

Examination of mechanisms of interaction of polyvinyl alcohol with optical bleaching agent

The rheological and spectrophotometric characteristics of polymer compositions containing optical bleaching agent were examined. The mechanism of interaction between the components of the polymer composition was studied.

Research of UV permeability properties of basic weft knitted structures

Sunlight is an indispensable life source for all organisms in the Earth. These rays arrive to the earth between 280 - 3000 nm wavelengths. Although, small doses of UV rays are useful for life, they cause effects such as sunburn, allergies, early aging in the skin, skin cancer, bruise formations and cataract on human body as far as this dose increases. These harmful effects are more seen in light skinned people. In this study the literature information was given concerning the definition of ultraviolet radiation (UVR) which is harmful sunlight’s, the relation between UVR and textile materials, is the protection from ultraviolet rays through textiles and the development of ultraviolet protective properties of textiles. As an addition to this information, after applied optical bleach and dying process on 100% cotton basic weft knitting fabrics, 4% absorber chemical substance was applied to these fabrics. After applied different treatment processes to these fabrics of different construction and grams, the effect of construction and grams on UV permeability of basic weft knit fabrics and the effect of processes on UV permeability were searched experimentally, and the found values were examined by means of formed tables and graphics. Key words: UVR, UPF, UV absorbent substance, weft knitting fabric.

Reduced bleaching in organic nanofibers by bilayer polymer/oxide coating

Para-hexaphenylene (p-6P) molecules exhibit a characteristic photoinduced reaction (bleaching) resulting in a decrease in luminescence intensity upon UV light exposure, which could render the technological use of the nanofibers problematic. In order to investigate the photoinduced reaction in nanofibers, optical bleaching experiments have been performed by irradiating both pristine and coated nanofibers with UV light. Oxide coating materials (SiOx and Al2O3) were applied onto p-6P nanofibers. These treatments caused a reduction in the bleaching reaction but in addition, the nanofiber luminescence spectrum was significantly altered. It was observed that some polymer coatings [a statistical copolymer of tetrafluoroethylene and 2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole, P(TFE-PDD), and poly(methyl methacrylate), PMMA] do not interfere with the luminescence spectrum from the p-6P but are not effective in stopping the bleaching. Bilayer coatings with first a polymer material, which should work as a protection layer to avoid modifications of the p-6P luminescence spectrum, and second an oxide layer used as oxygen blocker were tested and it was found that a particular bilayer polymer/oxide combination results in a significant reduction in bleaching without affecting significantly the emission spectrum from the nanofibers.