Study of the Properties of laser Beam Propagation Through the (ReactiveRed) dye
Saddam Flayeh Haddawi1*,Jinan Ali Abd2,
Wasan Mnati Mohmmed3,Hassan A.majeed4
University of Babylon, College of Science for women, Department of Laser Physics, Babylon, IRAQ
Shaddawi@yahoo.com
Abstract
The beam of laser properties in this research were studied, using the (He- Ne) laser ((? =632.8nm , p=1.04mw) optical system and beam of solid state laser (422nm ,P=14.64 mW). The parameters of the beam of laser such as spot, profile distribution ,and intensity in the (Reactive Red dye ) with concentration 10-9 mole L-1 were studied at different distance. Measurement was obtained by using a CCD camera. Absorption spectrum of the dye has been measured by using the Ultraviolet –Visible Spectrometer. Absorption coefficient value for Reactive Red was calculated in the two cases.
Key word: dyes, He- Ne laser solid state laser
1 – Introduction
The shaping of Laser beam that redistributes the phase and irradiance of an incident beam (usually Gaussian beam) to get a preferred distribution of intensity has been exhaustively studied using techniques of polarization and segmentation (1-7). Beam characteristics developed from the wavelength, polarization, beam waist radius, continuity and coherence of lasers and complex index of propagation medium deeply affect the applications (8). There are lots of applications in which the exact understanding of the diameter and divergence of the laser beam is critical (9). More fast and accurate measurements of the width of the laser beam are found by a CCD camera that offers a direct and real time view of the profile of laser beam (10). For an ideal Gaussian beam, this factor has been termed as M2 = 1. Beams of real laser have factors greater than 1. For example, lasers of helium neon typically have an M2 factor of less than 1. For many optical designs and laser measurements, the beam quality is important, where the M2 factor cannot be ignored (11). Many beams of lasers were emitted by a Gaussian profile, in this case the laser is supposed to work on the fundamental transverse or "TEM00” modes of the optical resonator of laser (12). The propagation during random media of the optical waves such the biological material, the ocean and the atmosphere is very significant for several applications as astronomical imaging and optical communications (13, 14).

Experimental part
1- Absorption spectral measurement for used Reactive Red
The spectrophotometer has been used to measure absorption and transmission spectra of the dyes in the range (190 – 800 nm). The light intensity, that is passing during a sample (I), measures and contrasts with the light intensity prior to pass throughout the sample (I?). I / I? ratio is named the transmittance and typically uttered as a percentage (T %). A, the absorbance, is estimated as of the transition.
A= - log (T/100) (15)
2- Measurement of two lasers beam profile in GRL dye at 10-7 of concentration
The spot, intensity and profile distribution of the laser beam is measured by two lasers systems, which are different in wavelength and power, solid state laser of (422nm and p=14.64mW) and He-Ne laser of (632.8nm and p=1.04mW). The factors as the shape, the laser beams intensity and the spot were determined by putting reactive dye of 10-9mole.L-1 of concentration in pure water, and located dye in the glassy tube and fixed it in a stand stuck between the CCD camera and the laser. Next as shown in figure (2), the beam of laser was centered to the centerof camera. After that as shown in figure (3), in the presence of the software in the computer, the best spot of the laser beam for all lasers was measured.

Figure (1) Experimental setup of the Red Reactive dye with concentration 10-9



Figure (2) image of the spot beam in the Reactive red dye

Result and dissection
1- Absorption spectral measurement for used GRL dye
Absorption spectrum of red reactive dye of (10-9) concentration was represented in Figure (3) at (UV-Visible) region. As shown in the figure, there are two maximum peaks, the first in UV region at 280 nm in and the second at 475nm in the visible region of the spectrum.

Figure (3) Absorption spectrum of Reactive Red with concentration of 10-9
2 – The beam of He-Ne laser in Red reactive dye of10-9mole.L-1 concentration
As shown in Figure ( a, b, c, d - 4), the fairly regular circular of the beam spot and the shape of the distribution intensity was Gaussian shaped for He-Ne laser at different distances (10,20,30,40) cm by Red reactive dye. While as shown in table (1), the intensity (peak values) werechanged (89.2, 92.7, 91.4, 95.8%) as the distances were changed (10, 20, 30, 40 cm) .

Figure (4) the spot and profile of of He-Ne laser beam at different distances
(a) 10 cm (b) 20 cm in Reactive Red Dye.

Figure (4) the spot and profile of of He-Ne laser beam at different distances
(c) 30 cm (d) 40cm in Reactive Red Dye.
Table (1) and Figure (5) show the variation of beam intensity and spot diameter with distance:
a- Intensity increases a little increased at distance 20cm and then occurs decrease at 30cm and then increase at value 92% .
b- Decrease mean until reached 30 and then a little increased from 30cm to 40cm.
C-Intensity increases until reaches maximum value at distance 40cm.




Table (1) variation of the diameter and peak of beam with the distances of He-Ne laser of Reactive Red dye


Figure (5) the intensity of peak and diameter variation with distances in
Reactive Red of He-Ne laser
3- Laser beam of solid state (422nm), P= 14.64mw in Reactive Red dye at concentration 10-9
As shown in Figure (6) there are different circular spots when using Reactive Red dye, and there was a small variation in the intensity distribution shape of Gaussian shape. It had been observed that the changing values of the intensity were irregular at different distance. The changing intensity values were (52.1, 41.2, 42.6, 37.6) %. as different values of distances (10, 20, 30, 40) cm Respectively, as shown in table (2). Concentration Reactive Red dye in water was a little effect on the shape spot and Gaussian distribution shape while the effect on the intensity was clear.


Figure(6 ) the spot and profile of solid state laser beam at different distances (a) 10cm (b) 20cm (c) 30 cm (d) 40 cm in Red Reactive Dye
Table (2) and Figure (7) show the variation of the intensity of beam and spot diameter with distance
a- decrease intensity until reached at distance 20cm then increase at distance 30 cm and then decrease at 40cm
b- Noticed that mean is decrease and then increase
c- Intensity is increase to distance 20cm and suddenly decrease at distance 40cm.

Table (2) variation of the diameter and peak of beam with the distances of solid state laser of Reactive Red dye



Figure (7) the intensity of peak and diameter variation with distances in
Reactive Red of solid state laser
4- The coefficient of absorption calculation of the Reactive Red dye
Coefficient of absorption of Reactive Red absorption for two laser systems of different powers and wavelength was calculated from equation (1).

Table (3) the absorption Coefficient of two lasers for Reactive Red dye

Conclusion
1- It was clearly that there was a relatively regular circular of the beams spot and the intensity shape of the distribution of He-Ne laser was shaped as Gaussian in air. Obviously there was changing in the shape of spot and intensity of distribution by using laser of semi-conductor system of short wavelength (422nm) and power of (14.64mW) and it was found a great broadening in the shape of the intensity distribution in air.
2- The coefficient value of absorption of the two cases was varied with the laser type.
3- The coefficient value of absorption of solid state laser was smaller so the laser might be using in under water communications.
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