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Possibility of Using the Beet Dyes As a Laser Gain Medium

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Vol.5, No.11, 1183-1188 (2013) Natural Science http://dx.doi.org/10.4236/ns.2013.511144 Possibility of using the beet dyes as a laser gain medium Abdelaziz Hagar Abdelrahman1,2*, Malik A. Abdelrahman3,4, Mohammed Khaled Elbadawy3 1Laser Institute, Sudan University for Science and Technology (SUST), Khartoum, Sudan; *Corresponding Author: [email protected] 2Physics Department, Collage of Science & Arts, Muznab, Qassim University, Qassim, KSA 3Chemistry Department (SUST), Khartoum, Sudan 4Chemistry Department, Collage of Applied Medical Sciences, (TURUBA), Taif University, Taif, KSA Received 27 July 2013; revised 27 August 2013; accepted 4 September 2013 Copyright © 2013 Abdelaziz Hagar Abdelrahman et al. This is an open access article distributed under the Creative Commons Attribu- tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT flow through the laser cavity to avoid thermal problems and the buildup of photo degradated dye molecules which Nowadays the dye lasers play as an important decrease the lasing efficiency [3]. tool and are used in many applications including The knowledge of fluorescence quantum efficiency of spectroscopy, medicine and dermatology. This organic dyes is important in selecting efficient dye laser research was carried out to study the possibility media [4]. Organic dyes dissolved in suitable liquid sol- of using the beet dyes as a laser gain medium. vent have found wide application in laser technology The fluorescence quantum yield was determined serving as an active gain medium for generation of co- by the comparative method with rodamine b as herent tunable radiation [5]. an organic dye standard. The value of the fluore- A dye laser is a laser which uses an organicdye as the scence quantum yield was found about (0.14) lasing medium, usually as a liquidsolution. For effective and the fluorescence quantum yield was devel- performance, dye molecules should have strong absorp- oped until reaching about (0.323). The increas- tion at excitation wavelength and minimal absorption at ing of fluorescence quantum yield of dye solu- lasing wavelength. Applications of lasers are wide and tion as a result of increasing the viscosity of varied today. They are found in communication tech- solvent was observed clearly. The study con- niques, microsurgery and medicine [6]. cluded that the beet dyes are so sensitive to fluorescence and it is very suitable to be used as 2. QUANTUM YIELD a laser gain medium. The quantum yield of a radiation-induced process is the Keywords: Beets; Lasing; Solvents; Quantum Yield number of times that a defined event occurs per photon absorbed by the system. Thus, the quantum yield is a 1. INTRODUCTION measure of the efficiency with which absorbed light produces some effect [7]. From the mid 60s, dye lasers have been attractive Quantum yield is essentially the emission efficiency of sources of coherent tunable radiation because of their a given fluoro chrome. Since not all photons are absorbed unique operational flexibility [1]. Light amplification by productively, the typical quantum yield will be less than 1 stimulated emission of radiation, that is lasers, has be- [8]. come an important tool in chemistry and many sciences. A The fluorescence quantum yield is defined as the ratio dye laser can be defined as a laser utilizing dye [2]. Some of the number of photons emitted to the number of pho- of the most popular and heavily investigated are the rho- tons absorbed or we can written as .[9]. damines and coumarins. Dye lasers have many advan- number of photons emitted tages over their liquid counterparts. They are nontoxic, QY (2.1) nonflammable, and can be engineered to be rugged and number of photons absorbed compacted by eliminating the dye flow hardware that is In comparative method, the same for different sample necessary in a liquid system. Liquid dye lasers rely on dye solutions compared under identical conditions of excita- Copyright © 2013 SciRes. OPEN ACCESS 1184 A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188 tion [9]. We may re-write Equation (2.1) as: Ax Fs QYxs QY (2.8) number of photons detected A F QY (2.2) s x fraction of light absorbedF where all terms on the right hand side of Equation (2.7) where α and β are constants related to the fraction of are known. It is assumes that measurements on solutions emitted light entering the light collection optics of the of X and S are made under identical conditions of excita- fluorimeter and the intensity of the excitation source at the tion wavelength and aperture settings. If different solvents excitation wavelength, respectively. In this equation, the are used for X and S, then Equation (2.7) should be further number of photons detected is the integrated area under modified to allow for the effect of refractive index on the the corrected fluorescence spectrum and the fraction of relative amount of fluorescence collected by the fluori- light absorbed (F) is obtained from the absorbance at the meter detection optics. The final equation for estimation excitation wavelength by; of fluorescence quantum yields by the Comparative Method then becomes: D F 110 (2.3) 2 AFxs n x where (D) defined as an optical density of a medium is the QYxs QY (2.9) AF n measure of its transmittance for a radiation of particular sx s wavelength. The relationship between the optical density where the ns and nx are the refractive indices of the sol- and transmittance (T) is an inverse, which expressed as vents used for the two solutions fluorescence spectra are [10]. always fully corrected using the installed correction D log 1 T (2.4) function of the Jobin Yvon Fluorolog spectro fluorimeter. 10 This function corrects for the variation with wavelength of Hence, for sample X, we can write: the sensitivity of the photomultiplier and the spectral A characteristics of the detection optics (gratings, mirrors, QY x (2.5) etc.) [9]. x F x In practice at nanotechnologies, solutions of quantum where Ax is the integrated area under the corrected fluo- yield material are compared with solutions of organic rescence spectrum. For a “standard” material, S, for which fluorophores of known quantum yield under the same the quantum yield of fluorescence is already known, we conditions of excitation. Absorbance’s of all solutions are can similarly write: adjusted so as to be preferably in the range (0.02 - 0.07) and not greater than ca. 0.1 at the excitation wavelength. If A s possible, it is best to arrange for the absorbencies of the QYs (2.6) Fs sample and standard solutions to be the same (or nearly Comparative measurements on solutions of sample X the same) at the exciting wavelength. Organic controls and a suitable standard, S, can then be used to estimate the that have been used are as shown in Table 1 [9]. fluorescence quantum yield of X by dividing Equation (2.4) by Equation (2.5): 3. CHOICE OF SOLVENT QY A F Prepared laser dye solutions usually contain very small x xs (2.7) quantities of dye. Typical dye concentrations are 10−2 to QY A F s sx 10−5 molar. For this reason, the solvent in which the dye is where upon the unknown constants α and β cancel out. dissolved plays an important role when defining physical Hence: properties and potential hazards. Table 1. Quantum yields determined by this method are reliable to about ±10%. Standard Solvent QY Fluorescence max (nm) Useful excitation range (nm) 9.10-diphenylanthracene Ethanol 0.90 406 - 4.27 320 - 370 Coumarin 1 Ethanol 0.70 450 320 - 370 Rhodamine 123 Ethanol 0.96 535 440 - 490 Rhodamine 6G Ethanol 0.95 560 450 - 500 Sulphorhodamine 101 Ethanol 0.95 600 500 - 550 Copyright © 2013 SciRes. OPEN ACCESS A. H. Abdelrahman et al. / Natural Science 5 (2013) 1183-1188 1185 Lasing wavelength and energy are very sensitive to the root vegetable known as the beetroot or garden beet. choice of solvent. Most laser dyes are polar molecules, However, other cultivated varieties include the leaf and excitation into their lowest-lying singlet state is ac- vegetables chard and spinach beet, as well as the root companied by an increase in the dipole moment. Ac- vegetables sugar beet, which is important in the produc- cordingly, solvent polarity plays an important role in tion of table sugar, and mangel-wurzel, which is a fodder shifting the lasing wavelength. In a majority of circum- crop. Three subspecies are typically recognized. All cul- stances, increasing solvent polarity will shift the gain tivated varieties fall into the subspecies Beta vulgaris curve toward longer wavelength. In the case of more polar subsp. vulgaris, while Beta vulgaris subsp. maritima, dyes, the shift can be as high as 20 - 60 nm. commonly known as the sea beet, is the wild ancestor of The output power of dye lasers is strongly dependent on these and is found throughout the Mediterranean, the the purity of the solvent. Impurities and additives may Atlantic coast of Europe, the Near East, and India. A strongly affect upper state lifetime of the dye or may second wild subspecies, Beta vulgaris subsp. adanensis, catalyse photochemical reactions. Therefore, for best occurs from Greece to Syria. results, only high quality solvents are to be recommended Betacyanins (Bc) is extracted dyes from beetroot or [11]. beet red (Beta vulgaris). The two hydro-soluble com- With the exception of water, all solvents should be pounds: betacyanin (Bc) and betaxanthins (Bx), which considered hazardous. In many instances, the solvent in present absorption bands at 540 and 480 nm, respectively which the dye is dissolved plays a major role in the hazard are obtained from aqueous extraction of beet red [13] as presented by the final solution.
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