Study of Output Lasers of Rhodamine 6G Pumped by N2laser

Full Length Research Paper

Study of output Lasers of Rhodamine 6G pumped by N2laser

A.H. Abdelrahman Physics Department, Collage of Science& Arts Muznab, Gassim University, KSA

Accepted 8 April 2014

Abstract: In this work, dyes (Rhodamine 6G) dye was dissolved in three different solvents (acetone, methanol and ethanol) with two concentration levels values (1.4 & 1.6) g/l). Optical properties of dyes solvents and solutions were successfully determined. These solutions optically pumped by N2 laser (337nm) using Hansch cavity configuration to produce laser. The results of these detailed found that the (Rhodamine 6G) dyeis so sensitive to use as a laser gain medium with the concentration 1.6g/l. The output peaks of Rhodamine 6G dye dissolved in acetone, ethanol but in methanol concentration (1.6, 0.8, and 0.4g/l) at (572.61, 574.05, 571.54, 575.12and 573.69nm) respectively.

Keywords: Rhodamine 6g, laser, pumped, solvent

Introduction Nowadays, the Dye lasers used in many applicationsas spectroscopy, medical, photochemistry. [1,2] The structure and composition of a laser dye has an important influence on the spectral emission from a dye laser. Many of laser dyes are available for use in the gain medium of a dye laser. Energy may be emitted from the ultraviolet to the near infrared by using different dyes. In this research,Rhodamine 6G dye pumped by N2 laser was used to determine the absorption and emission of it. Many different techniques have been used to excite the gain medium in dye lasers (another laser or flash lamb); this has led to the generation of an output beam of ultra-short pulses, in the femto second class, to continuous wave output from a similar dye laser scheme.[3] In the absence of shielding the interaction with the surrounding medium would cause non-radiative (collisional) decay to dominate. In that case, the energy lost when the electron jumps to the ground state would be transferred to the surrounding medium, thereby heating up the medium. [4] The use of solid matrices containing laser dyes is an attractive alternative to the conventional liquid dye solutions. The first solid-state dye lasers demonstrated stimulated emission from polymeric matrices doped with organic dyes. However work on solid-state dye lasers was not pursued for over a decade due to low lasing efficiencies and fast photo degradation of the dye. The structure and composition of a laser dye has an important influence on the spectral emission from a dye laser[5]. Many of laser dyes are available for use in the gain medium of a dye laser. Energy may be emitted from the ultraviolet to the near infrared by using different dyes. ______Correspondence Email:: [email protected]

. Solvents Solvents and solutes can be broadly classified into polar and non-polar. The polarity can be measured as the dielectric constant or the dipole moment of a compound. The polarity of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible. Asa rule of thumb, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: Laser dyes often dissolve in arrange of solvents, in fact, the solvent can have a very strong influence on the emission, governing of output power, as well as influencing the rate of degradation of the dye solution. Prepared laser dye solutions usually contain very small quantities of dye. Typical dye concentrations are 102 to 105 molar. Lasing wavelength and energy are very sensitive to the choice of solvent. Most laser dyes are polar molecules, and excitation into their lowest-lying singlet state is accompanied by an increase in the dipole moment. Accordingly, solvent polarity plays an important role in shifting lasing wavelength. In majority of circumstances, increasing solvent polarity will shift the gain curve towared longer wavelength. In the case of more polar dyes, the shift can be as high as 20-60 nm. Although very often a specific is recommended for use with a particularly dye, it is important to recognize that other solvents can also be used, particularly if the user is interested in shifting the gain curve to different wavelengths. The most common solvent in everyday live is water. Most other commonly used solvents are organic chemicals. These are called organic solvents. Solvents usually have low boiling point and evaporate easily, or can be removed by distillation, thereby leaving the dissolved substance behind. Solvents should therefore not react chemically with the dissolved compounds. Solvents can also be used to extract soluble compounds from a mixture. Solvents are usually clear and colorless liquids and many of them have a characteristic Oder. The concentration of a solution is the amount of compound that is dissolved in a certain volume of solvent. The solubility is the maximal amount of compound that is soluble in a certain volume of solvent at a specified temperature. Different solvents cause slight shifts in the energy levels of dye molecules, leading to slight variations in the radiative spectrum of those molecules. In order to be used in a dye laser, the solvents must be transparent for both the pump radiation and the laser wavelength (9, 15). We used three different solvents in this work.

Acetone This chemical compound (also known as propane, dimethly1 ketones) is the simplest representative of the ketones. The molecular formula of it is CH3COCH3. Acetone is a colorless, mobile, flammable liquid with melting point of -95.4 C and boiling point of 56.53 C. It has a relative density of 0.819 (at 0 C). It is readily soluble in water, ethanol, ether, etc, and itself serves as an important solvent. [6]

Methanol Methanol, known as methyl alcohol, is a chemical compound with chemical formula CH3OH. It can be described as colorless and poisonous liquid with a distinctive smell, so it should be kept carefully. We must put the methanol in suitable containers tightly closed and keep it away from sources of ignition because it is a volatile and flammable solvent. It is a polar solvent used to dissolve laser dyes like cyanine and Rhoda mines and it can be used as antifreeze. It can be considered as an ideal solvent for UV-pumped dye lasers because of its transparency. Methanol is usually containing 0.01-0.04% water[4,6].

Ethanol Ethanol, also known as ethyl alcohol or green alcohol, is a flammable, colorless, slightly toxic chemical compound. Its molecular formula is C2H6O. At the molecular level, liquid ethanol consists of hydrogen-bonded pairs of ethanol molecules. Ethanol is used as a solvent in dissolving laser dyes. Ethanol can dissolve both polar and non-polar substances. Organic solids of low molecular weight are usually soluble in ethanol. Among ionic compounds, many monovalent salts are at least somewhat soluble in ethanol, with salts of large, polarizable ions being more soluble than salts of smaller ions. Most salts of polyvalent ions are practically insoluble in ethanol. [6] In addition, like the methanol, it should be placed in suitable containers appropriately labeled.

Criteria for the choice of appropriate solvents for laser dyes are 1. The solvent must be transparent at the pump wavelength and the emission wavelength of the dye laser. 2. The dye should be soluble in the solvent under consideration. 3. The solvent must be photo chemicallystablewhen exposed to the pump light (15).

Literature review In 2000 Ulrich Brack Mann studied the absorption and emission of Coumarin 500 and Rhodamine 6G dyes and determines the Absorption maximum of coumarin500 in ethanol is 395nm and the emission peak is 503 nm with concentration 1.4g/l and the efficient laser dye for pulsed operation tunable around 500nm. In addition, Rhodamine 6G absorbance maximum wavelength is 530and the emission is 556nm.When this dye pumped by nitrogen laser, and the emission peak is 581nm in methanol with concentration 1.6g/l.Moreover, the efficient laser dye for pulsed operation tunable around 590nm [4]. Bushra Ahmed Izeerig in 2011 studied the enhanced optical properties of coumarin500 dye blended with gum Arabic. This study presented the effect of gum Arabic on the absorption and emission spectrum of coumarin500 dye and found the emission peak is 499.2nm [7].

Experimentalsetup

In this chapter, all materials used in the experiments and the procedureare described.

Rhodamine 6G

Dye was defined as an organic compound which can absorb and emit not in the visible spectrum only but also in the ultraviolet and near infrared. Here we used two different dyes dissolved in two different concentrations (1.4 and 1.6g/l) [4]. Rhodamine 6Gis afamily of related chemical compounds, fluorine dyes,examples are Rhodamine B and Rhodamine 6G.The chemical formula of this dye is C28H31N2O3Cl as shown in Fig.(1).Its molecular weight (mw) is 479.02g/mol, and its appearance is red solid. The absorbance maximum wavelength is 530and the emission is 556nm.When this dye pumped by nitrogen laser, and the emission peak is 581nm in methanol with concentration 1.6g/l.Moreover, the efficient laser dye for pulsed operation tunable around 590nm [4].

Fig. (1) Chemical formula of Rhodamine dye.

UV-VIS spectrophotometer

This device was used to measure the absorption and the transmission of the solutions and solvents before using in cavity its covering a wavelength from 190-1100 nm with auto lamp switch from visible to ultraviolet range. UV- VIS spectrophotometer from SHIMADZO contains a cell of thickness 0.1mm as a sample holder. . Upon completion of the spectral scan, the peaks and valleys can be marked within a few seconds; Optical specifications of UV – VIS 1240 Spectrophotometer are listed in Table (1). The standard peak pick function allows for clear and accurate detection of the most sensitive wavelengths[8].

Table (1): Optical specifications of UV – VIS 1240 spectrophotometer.

Wavelength range 190 nm to 1100

Display wavelength 0.1 nm step (1nm step in spectrum mode)

Monochromator Incorporates aberration-correcting concave blazed holographic grating

Light source Auto adjustment for maximum sensitivity correction with the computer memory halogen lamp and deuterium lamp

Measurement method Single beam measurement

Detector Silicon photodiode

The UV 1240 spectrophotometer may connected to PC via the standard RS_232C port the UV Data manager software designed to help organize and store data files in memory of computer ,the spectrophotometer or data packs (9).

USB2000 fiber optics spectrometer

Is a small-foot print, plug and-play, ocean Optics Company as shown in table (2). It automatically reads the wavelength calibration coefficient of the spectrometer and configures operating software. We use with it light sources, collimating lenses, sampling holders, filter holders, flow cell, fiber optic probes and sensors, and optical fibers to create the optimal system for their application. We used it to detect the florescence, emission and laser output. It can detect wavelength from 400-1100nm.

Table (2): The specifications of USB 2000 spectrometer.

Wavelength Numerical aperture Fiber core Fiber profile Cladding jacketing optimization

200-1100 nm 0.22+/-0.02(24.80) Pure Step-index multi- Doped fused Silicone silica mode silica Monocoil

* SMA Connector:The SMA Connector secures the input fiber to the spectrometer. Light from the input fiber enters the optical bench through this connector. * Slit:The Slit is a dark piece of material containing a rectangular aperture, which is mounted directly behind the SMA Connector. The size of the aperture regulates the amount of light that enters the optical bench and controls spectral resolution. * Filter:The Filter is a device that restricts optical radiation to pre-determined wavelength regions. * Collimating Mirror:The Collimating Mirror focuses light entering the optical bench towards the Grating of the spectrometer. * Grating:The Grating diffracts light from the Collimating Mirror and directs the diffracted light onto the Focusing Mirror. * Focusing Mirror:The Focusing Mirror receives light reflected from the Grating and focuses the light onto the Detector. * L2 Detector Collection Lens:The L2 Detector Collection Lens (optional) is attached to the CCD Detector. It focuses light from a tall slit onto the shorter CCD Detector elements. The L2 Detector Collection Lens should be used with large diameter slits or in applications with low light levels. * CCD Detector (UV or VIS):The CCD Detector collects the light received from the Focusing Mirror or L2 Detector Collection Lens and converts the optical signal to a digital signal. The spectrometer then transmits the digital signal to the OOIBase32 application. OOIBase32 is operating software for all Ocean Optics spectrometers; OOIBase32 is a user-customizable, advanced acquisition and display program that provides a real-time interface to a variety of signal-processing functions. With OOIBase32, user has the ability to perform spectroscopic measurements (such as absorbance, reflectance, and emission), control all system parameters, collect and display data in real time, and perform reference monitoring and time acquisition experiments [9]. nThe CUV-ALL 4-WAY is a cuvette holder for 1 cm cuvettes that has fiber optic couplings at four collimators, the cuvette holder that attaches directly to light

sources. When combined with the spectrometers and light sources, it can measure absorbance, fluorescence, scattering, or any combination of these optical phenomena.

Transmission, absorption and emission measurements The transmissions of solvents using UV-VIS spectrophotometer were measured to be sure that they were transparent in the range 190 to 1100nm. The two dyes were dissolved in the solvents and its absorption was measured to know the suitable pump source, which is convenient to the absorption wavelength using UV-VIS also. To measure the emission of these solutions we used the USB spectrometer with its operating software OOIBase 32.

N2LASER A home built N2 laser in AL-Neelain University was used to pump source for dyes in our experiments. It is composed of a laser tube, spark gab capacitors, and high voltage. Its output wavelength is337nmand power 0.04mW.

Hansch cavity Laser was used for pumping the dyes, a quartz cuvet to put the solutions inside the cylindrical lens, a grating that can be rotated, an end mirror, a fabry-Perot (etalon) also can be rotated, a pinhole, and telescope composed of two lenses L1 and L2. This configuration is known by Hansch cavity design. The N2-laser beam passes the cylindrical lens in a rectangular cross-section from to focus it onto the front face of the dye cell. If the focusing is correct, a narrow beam of fluorescence will emerge from other side of the cuvet. The optical cavity was about 40cm, it contains a tuning grating at one end and at the other end,and there is a plane mirror. The output of the high-gain laser medium pass the telescope to make the beam more collimated when arrived to the diffraction grating, which is used to make the beam sharper. We can get a narrow beam of output by rotating the grating and the Fabry-Perot etalon [10] as shown in Fig. (2) (3.4).

Nitrogen Iaser

Cylindrical Pinhol Iens e L L 2 1 laUT put laser Mirror Dye cell

Telescope Grating Fabry- PerotEtalon

Fig. (2) schematic diagram of Hansch cavity

The procedure: Conclusion of 0.050 g /36 ml and 0.0502 g /31 ml of rhodamine 6G of the sample was prepared, and then diluted (0.8 - 0.4) g/l of rhodamine 6G solve in methanol. Using the UV- VIS spectrophotometer, the transmission, absorption and emission were measured. Then, nitrogen laser system was used. The laser beam was obtained by moving the cell, mirror, and grating, was recorded as analog signal.

RESULTS

In this chapter the resultsis presented obtained during our work and their analysis. The results obtained by using the nitrogen laser available in the laser applications laboratory of Al-Neelain University and delivering output laser of 337nm. Dyes were dissolved in different solvents like acetone, methanol and ethanol with two concentrations (1.4 and 1.6g/l) rhodamine 6G.The pumping beams characteristics were fixed during the experiments.Below are the obtained results.

5characteristics of the materials used The characteristics (transmission, absorption and emission) of solvents and dyes were measured to be sure that they are in the spectral range of our experiments.

Transmissions of solvents The transmission of the three solvents was measured using UV-VIS spectrophotometer and it is shown in Figs. (3), (4) and (5).

130 120 ethanol transmission 130 110 120 acetone transmission 100 110 90 100 80 90 80 70 70 60 60 50

transmission% 50 transmission% 40 40 30 30 20 20 10 10 0 0 300 350 400 450 500 550 600 650 700 750 800 200 250 300 350 400 450 500 550 600 650 700 750 800 wavelength(nm) wavelength(nm) Fig(3). Transmission of acetone.Fig(4). Transmission of ethanol.Fig(5). Transmission of methanol. These figures show the transmission spectra of acetone, ethanol, and methanol, respectively. It is clear that all of the three solvents are fully transparent between 300-800nm, leading to the conclusion that the nitrogen laser energy is not affected the solvents in use.

Absorption and emission of Rhodamine 6G dyes

Absorption and emission are very important characteristics in dye lasers. We can choose the suitable pumping source depending on the absorption peaks.

1.1 527 610.75 absorption 1.0 emission 0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2 NormalizedAbs./Emis.(a.u.) 311 270 0.1234

0.0 300 400 500 600 700 800 900 1000 1100 215.5249.5312.5 wavelength(nm)

Fig (6) Absorption and emission of Rhodamine 6G dye dissolved in acetone.

531600.1 absorption 1.0 emission

0.8

0.6

0.4

0.2 292.5 NormalizedAbs./Emis.(a.u.)

0.0 200 300 400 500 600 700 800 900 1000 1100 wavelength(nm) Fig (7) Absorption and emission of Rhodamine 6G dye dissolved in ethanol.

1.1 529 594.41 absorption 1.0 emission 0.9

0.8

0.7

0.6

0.5

0.4

NormalizedAbs./Emis.(a.u.) 0.3 292.5 0.2 347.5

0.1

0.0 319.5 300 400 500 600 700 800 wavelength(nm) Fig (8) Absorption and emission of Rhodamine 6G dye dissolved in methanol.

Figs. (6), (7) and (8) show the absorption and emission spectra of the second dye (Rhodamine 6G) dissolved in acetone with absorption peak is at527 nm and emission peak at610.75 nm. In ethanol, the absorption peak is at531 nm and the emission peak at600.1 nm. Finally, at529 nm is the absorption peak and at594.41 nm is its emission peak in methanol.Table (3) below shows the main parameters of Rhodamine 6G in different solvents.

Table (3): The basic parameters of Rhodamine 6G dye.

Solvents Parameters Acetone Ethanol Methanol Absorption (nm) 527 531 529 Emission (nm) 610.75 600.1 594.41 Stoke shift (nm) 83.7 69.1 65.4

The output obtained with Hansch Cavity:

Rhodamine 6G dyes were dissolved in the solvents chosen with concentrations 1.4 g/l and 1.6 g/l.Nitrogen laser pumped the medium.The follow figures showed asset of graphs of output beam power against the wavelength.

In Fig. (9), the solvent used was acetone. With concentration 1.6g/l the emission peak was at572.61nm. Methanol was the solvent used as seen in Fig. (10a), (10b), (10c), shows the emission peak at571.54nm with 1.6g/l, the emission peak at575.12 nm with 0.8g/l, while for concentration 0.4g/l it is at573.69nm, respectively. In addition, in Fig. (11), the solvent used was ethanol. Its emission peak was at574.05nm with concentration1.6g/l.

3500 571.54 Rhod Methanol 3500 572.61 Rhod Acetone 3000

3000 2500 2500 2000 2000

1500 Emis.(a.u.) Emis.(a.u) 1500

1000 1000

500 500

0 0 400 500 600 700 800 900 1000 400 500 600 700 800 900 1000 wavelength(nm) wavelength(nm) Fig. (9) Output of Rhodamine dye dissolved in acetone.Fig. (10a) Output of Rhodamine dye dissolved in methanol

1600 Rhod methanol 573.69 575.12 Rhod methanol 1400 2500

1200 2000 1000

1500 800

1000 Emis.(a.u.) Emis.(a.u.) 600

400 500

200 0 0 300 400 500 600 700 800 900 1000 1100 300 400 500 600 700 800 900 1000 1100 wavelength(nm) wavelength(nm)

Fig. (10b) Output of Rhodamine dye dissolved in methanol.Fig. (10c) Output of Rhodamine dye dissolved in methanol.

1800 574.05 Rhod ethanol

1600

1400

1200

1000

Emis.(a.u.) 800

600

400

200

0 400 500 600 700 800 900 1000 wavelength(nm)

Fig. (11) Output of Rhodamine dye dissolved in ethanol.

Table (4): Specification of the emission obtained with Hansch cavity. Parameters λ(nm) Δλ(nm) O/P(a.u.) Concentration(g/l) Solvents 1.6 Acetone 572.61 6.7 3371.10 1.6 Methanol 571.54 6.7 3194.15 0.8 Methanol 575.12 19.3 2507.75 0.4 Methanol 573.69 21.5 1399.64 1.6 Ethanol 574.05 5.1 1720.48

Table (5): Show specifications of the laser beam obtained from the hansch cavity. Characteristics Laser beam output Typical value obtained Laser wavelength(λmax)(nm) 572.61 574.05 573.69 573-618 FWHM (Δλ)(nm) 6.7 5.1 6.7 25-30 Dyes concentration*10- 1.6 1.6 1.6 10-3-10-4 3(molar) Solvents Ace eth meth eth,meth Operating temperature Room temperature Room temperature Mode of operation Pulsed Pulsed Pumping method Optical ( laser) Optical ( laser)

Discussion

In our trails to obtain laser we used cavity configurations of the type Hansch cavity design. For Rhodamine 6G dissolved in different solvents with concentration (1.6g/l), in acetone, ethanol but in methanol concentration (1.6, 0.8 and 0.4g/l). The output peaks of Rhodamine 6G dye dissolved in acetone, ethanol but in methanol concentration (1.6, 0.8, and 0.4g/l) at (572.61, 574.05, 571.54, 575.12and 573.69nm) respectively. The emission obtained

from these media represented laser signal. The obtained laser wavelengths from the Rhodamine 6G dyeIS presented in tables (4). Rhodamine 6G, the absorption peaks are 527, 531, and529nm, respectively. There were shifts in its absorption spectra about (1-3) nm in comparisons with literature [4].Moreover, the emission peaks had a shift of about 54, 44 and 38nm respectively between these peaks and the peaks found in literature (556nm) [11].

Conclusion

From the results obtained in the previous chapter, it was observed that:  The solvents (acetone, ethanol and methanol) used were suitable for the dyes selected. They were highly transparent, which mean that they did not reduce the incident energy used for pumping the dye molecules.  In principle, the two laser dyes were optically characterized. We notice that the full width at half maximum (FWHM) of the laser beams are smaller than the others due to the properties of laser .  The relation between the concentrations and the wavelengths was measured; the results showed that when the concentration increases the wavelength increases.  The intensity of the laser output beam changes from solvent to another and the results showed that rhodamine 6G is very good laser dye medium.

References

1- Drexhage, K. H, Structure and Properties of Laser Dyes in Topics in Applied Physics, Dye Laser Springer-Verlag, Berlin, Germany, (1990), p 21-22, 167-169. 2- William T. Silfast.” Laser Fundamentals”, 2nd edition, Cambridge University Press (2004). 3- Ulrich Brack Mann.‟‟ Lambdachrome: Laser Dyes‟‟, 3rd Edition Lambda Physik (January 2000). 4- Frank L. Pedrotti, S. J. lenos. Pedrotti. “Introduction to optics”, 2and edition prentice. Hall. Inc. New jersy. (1993). 5- G S Shankarling and K J Jarag, Laser Dyes,September 2010. 6- H. H.Amir, R.R. Paxton,Matthew Van Winkle, Methanol –Ethanol- Acetone, Ind. Eng. Chem., 1956, 48 (1), pp 142–146 7- Bushra Ahmed Izeerig.‟‟Enhanced Optical Properties of Coumarin500 dye blended with Gum Arabic‟‟. M. Sc. Thesis, EL-Neelain University, Khartoum, Sudan. (2011). 8- Shimadzu Spectrophotometer UV Mini 1240‟‟, Operation Manual. 9- USB 2000 – Fiber Optic Spectrometer, Installation and Operation Manual. 10- Hussein Gar alnaby Abdullah Teih. „‟Testing of Manually Operated Hansch Cavity for Some Laser Dyes‟‟. M. Sc. Thesis, EL-Neelain University, Khartoum, Sudan. (2005). 11- Henry R. Aldag David H. Tittron, „‟ from flash lamp pumped liquid dye laser to diode-pumped solid-state dye laser ‟‟, Presented at SPIE Photonics, west (January 2005).

Cite this article as: Abdelrahman (2014). Physics Department, Collage of Science& Arts Muznab, Gassim University, KSA. Sci. Res. Impact. 3(1): 32- 42.

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