CC BY
3CHARACTERISTICS OF RADIATION OF THE LAYER EXCITED BY THE LIGHT OF THE R6G ALCOHOL SOLUTION OF THE RECTANGULAR GEOMETRICAL
FORM OPTICAL CELL
Wardosanidze Zurab V.
PhD, Lead Researcher, Institute of Cybernetics of Georgian Technical University Oniani David
Technician, Institute of Cybernetics of Georgian Technical University Nakhutsrishvili Irakli
PhD, Senior Researcher, Institute of Cybernetics of Georgian Technical University Tkhinvaleli Rafiel
PhD, Senior Researcher, Institute of Cybernetics of Georgian Technical University
The divergence of laser radiation depends on the design of the resonator and its geometric dimensions (the diameter of the active element and the length of the resonator). For cavity less lasers (for example, for fiber lasers), the radiation divergence depends on the diameter of the active medium. The present lecture concern to the laser with plane directional circular radiation. In particular, the spectral and spatial characteristics of the lateral radiation of a layer of Rhodamine 6G solution, with a regular geometric shape, were experimentally studied.
The studied layer is a part of the laser dye solution, which is in optical contact with the bottom of optical rectangular cell, the shapes of which determine the geometric shape of the excited layer.
The investigated layer in combination with an optical cell can be considered as a monolithic ring resonator (MRR), operating on the basis of total internal reflection (TIR) [1,2]. In this case, the main directions of maximal Q-factor (lasing) inside of cells, must satisfy n^-the condition
„ . n
of total internal reflection (TIR): a = p> arcsin —,, where a = P are the angles of incidence
n2
and reflection, n2is the refractive index of the optical cell wall, n1 is the refractive index of air. The main directions coincide with the sides of the inscribed rectangles parallel to the diagonals, which can ensure lasing, practically, in the entire dye layer (Fig. 1).
Fig. 1. Main directions of intracavity lasing (MRR - TIR) for rectangular cell.
For observing and investigation of radiation of the dye solution layer, the experiments were carried out with an alcohol (ethyl alcohol) solution of the laser dye Rhodamine 6G, placed in rectangular and cylindrical optical cells made of isotropic optical glass K8 with a refractive index Hg=1.51. The alcohol solutions of Rodhamine 6G (R6G) were prepared with various concentrations: 0.15, 0.12, 0.09, 0.06 and 0.03 wt%; with an average refraction index «2=1.37.
Inside size of the rectangular cell is 18x20mm and the thickness of their glass walls is 3mm, quite satisfying the conditions of a MRR. Optical excitation (pumping) was carried out by the second harmonic of a Nd: YAG (X = 532nm), from the side of the bottom of the optical cell, at a strict perpendicularity of the luminescent layer of the dye solution to the walls of the cell and to the pumping beam.
Was investigated the spectral characteristics of radiation in the different dye concentrations in solution. It turned out that with a decrease in the concentration of the dye, the peak energy of the radiation pulses increases and reaches the saturation value (Fig. 2).
Pumping
7000060000-з 50000-
^ 40000-&
300000)
2000010000500 520 540 560 580 600 620 640
Wavalength, (X,nm)
Fig.2. The spectrums of emission of the excited layer for the different concentrations of the dye (1 - 0.12, 2 - 0.09, 3 - 0.06, 4 - 0.03wt%) for the rectangle cell.
The spectral curves of the radiation of the excited layer of the solution were obtained at identical pump radiation energy (X =532 nm). According to Fig.2, with a decrease in the concentration of the dye from 0.12wt% to 0.06wt%, the radiation energy increases from the very beginning, and at a minimum concentration of 0.03wt% it already decreases, which is probably associated with concentration effects (concentration quenching, quantum yield). At the same time, with a decrease in the concentration of the dye, the radiation spectrum narrows and already at a concentration of 0.03 (wt%), the half-width of the radiation spectrum reaches 3-4 nm, which is typical for superradiance, superluminescence, and even for lasing (Fig.2 (4)). A further decrease in the concentration of the dye leads to a significant decrease in the intensity of radiation and to a broadening of the emission spectrum up to usual luminescence.
So, was obtained narrowband (3-14nm) radiation of the thin layer, of rectangle geometrical form, of the laser dye R6G solution. This radiation is characterized with uniform circular distribution of emitted light in the layer plane with sufficient low vertical divergence (2-10mrad). So, was obtained narrowband (3-14 nm) radiation of the thin layer, of rectangle geometrical form, of the laser dye R6G solution. This radiation is characterized with uniform circular distribution of emitted light in the layer plane with sufficient low vertical divergence (2-10mrad). With a change in the dye concentration, the penetration depth of pump radiation into the dye solution (in the case of linear absorption) changes according to the law [3, 4]: d =
ini0 ln,act,where I0 is the intensity of the incident pump light, Iact is the intensity of the
kx
penetrated pump light in the absorbing solution of the dye which is sufficient for the population inversion, and kX is the absorption coefficient at the pump wavelength X=532nm.
From the point of view of applied optics, the resulting laser with circular, plane directional radiation can be used in both ground-based and aerospace navigation systems. It can also be used in optical information technology, photonics, spectroscopy as well as holography to display large-scale 3D scenes [5, 6].
References:
1. S.Schiller, M.M.Fejer, R.L.Byer, A.Sizmann, M.Karim.Monolithic total internal reflection resonators: principles and applications.Conference on Lasers and Electro-Optics, Anaheim, California United States. 10-15 May 1992, 1-2, 10-15.
2. G.Lin, Y.K. Chembob.(INVITED) Monolithic total internal reflection resonators for applications in photonics.Optical Materials: X, 2019, 2, 100017(1-13).
3. M.Born, E.Wolf. Principles of Optics, 1964, Second (Revised) Edition, Pergamon Press, 936.
4. R.W.Wood. Physical Optics. 1988, 3rd ed., Optical Society of America, Washington, 46.
5. Z.V.Wardosanidze. Radiation of the Light Excited Layer of the Alcohol Solution of the Dye Rhodamine 6G. European J. Appl. Sciences,2021, 9, 4, 197-206.
6. Z.V.Wardosanidze. Circular, Plane-Directional Radiation from the Edges of a Light-Excited Layer of a Laser Dye Solution with the Regular Geometric Form. Intern. J. Opt. and Photonic Eng., 2021, 6, 041, 2-10.
