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Optical distortion in a nitrogen laser pumped, dye laser
Volume 15, number 2
OPTICS COMMUNICATIONS
October 1975
OPTICAL DISTORTION IN A NITROGEN LASER PUMPED, DYE L A S E R M.M. LOIKO Physical lnstitute o: the Bielorussian Academy of Sciences, Minsk, USSR and ZS..BOR, L. KOZMA, B. RACZ and I. KETSKEMI~TY Institute of Experimental Physics, Attila J6zsef University, Szeged, Hungary Received 11 June 1975, revised manuscript received 28 July 1975
The deviation of the laser beam from the axis of a nitrogen laser pumped, dye laser cavity is investigated. It is found that the angle of deviation depends on the dye concentration, on the solvent and on the pumping power.
In the present paper an effect observed by the authors, concerning the deviation of the beam from the axis of a nitrogen laser pumped, dye laser cavity is described. This effect develops during the lasing, as it can be observed to the same extent b o t h at a repetition frequency of 0.1 Hz and at single pulse operation. Thus this effect does not occur only at higher repetition frequencies, as the Schlieren phenomena described in ref. [1 ]. The experimental arrangement used is shown in fig. 1. The radiation o f the nitrogen laser o f 250 kW peak power and 5 nsec pulse duration is focused by a cylindrical lens on the cuvette containing the dye solution. The generation o f the dye laser is produced in transverse arrangement without external mirrors, between the walls o f the cuvette which has an active path length o f 1 cm. The dye is uniformly excited throughout the full path length o f the cuvette.
I Z
cuvetteo~?~
3371,~ Fig. 1. Experimental arrangement.
Table 1 Dye, solvent
Rhodamine 6G, ethanol
Fluorescein, ethanol
c k (mole/~) (cm -1 )
cz (mrad)
2×10 -3
30
11
4×10 -3 1Xl0 -2
60 150
12 16.5
2X10 -2
300
22
4X10 -2
600
29
5×10 -3
42.5
10.4
1×10 -2
85
10.9
Fluorescein, H20
5X10 -3
-
7-diethilamino-4-methylcoumazin, ethanol
1 × 10 -3 1 X10-2
25 250
9.4 83 66
Table 2 c(mole/•)
2 × 10 -2
U(kW)
150
~(mrad)
22
4 X 10-2 90 17.5
150
90
29
24
We found that the direction o f the light beam of the dye laser does not coincide with the X axis o f the resonator and deviates by an angle a in the direction o f propagation o f the exciting radiation (see fig. 1). 173
Volume 15, number 2
OPTICS COMMUNICATIONS
The angle a depends on the properties and the concentration of the dye, on the solvent and on the pumping power. The results of the measurements are given in tables 1 and 2, where c is the dye concentration in mole/~, k the absorption coefficient of the solution at the pumping wavelength (~ = 337.1 nm), ot the deviation of the dye laser beam from the resonator X axis, and U the peak pumping power. (Table 2 presents the data for the dye Rhodamine 6G.) The observed effect indicates that the pumping radiation induces a refractive index gradient in the Z direction. Further investigations showed that the deviation of the laser beam from the optical axis is not caused by the non-parallellity of the cuvette walls. The refractive index gradient in the excited dye may be ascribed to the following causes: 1. The temperature gradient produced by the exponential decrease of the pumping intensity and the heating effect with depth of the solution.
174
October 1975
2. Shock waves produced by the pumping pulse in the zone of generation. 3. The population of the excited state decreasing with the depth of the solution, having a maximum at Z = 0, while the population of the ground state shows an inverse change. Proceeding further in the direction of the Z axis the refractive index of the solution depends linearly on the concentration of the excited states, therefore the changes in the population of the ground and the excited states with the depth of the solution may lead to an increase of the refractive index in the Z direction Further investigations are necessary for a rigorous quantitative analysis of the observed effect.
References [1] G.A. Abakumov, M.A. Kasimdjanov, V.P. Protasov, A.P. Simonov, V.V. Fadeev and P.B. Khokhlov, Zhur. Prikl. Spektr. 15 (1971) 415.
OPTICS COMMUNICATIONS
October 1975
OPTICAL DISTORTION IN A NITROGEN LASER PUMPED, DYE L A S E R M.M. LOIKO Physical lnstitute o: the Bielorussian Academy of Sciences, Minsk, USSR and ZS..BOR, L. KOZMA, B. RACZ and I. KETSKEMI~TY Institute of Experimental Physics, Attila J6zsef University, Szeged, Hungary Received 11 June 1975, revised manuscript received 28 July 1975
The deviation of the laser beam from the axis of a nitrogen laser pumped, dye laser cavity is investigated. It is found that the angle of deviation depends on the dye concentration, on the solvent and on the pumping power.
In the present paper an effect observed by the authors, concerning the deviation of the beam from the axis of a nitrogen laser pumped, dye laser cavity is described. This effect develops during the lasing, as it can be observed to the same extent b o t h at a repetition frequency of 0.1 Hz and at single pulse operation. Thus this effect does not occur only at higher repetition frequencies, as the Schlieren phenomena described in ref. [1 ]. The experimental arrangement used is shown in fig. 1. The radiation o f the nitrogen laser o f 250 kW peak power and 5 nsec pulse duration is focused by a cylindrical lens on the cuvette containing the dye solution. The generation o f the dye laser is produced in transverse arrangement without external mirrors, between the walls o f the cuvette which has an active path length o f 1 cm. The dye is uniformly excited throughout the full path length o f the cuvette.
I Z
cuvetteo~?~
3371,~ Fig. 1. Experimental arrangement.
Table 1 Dye, solvent
Rhodamine 6G, ethanol
Fluorescein, ethanol
c k (mole/~) (cm -1 )
cz (mrad)
2×10 -3
30
11
4×10 -3 1Xl0 -2
60 150
12 16.5
2X10 -2
300
22
4X10 -2
600
29
5×10 -3
42.5
10.4
1×10 -2
85
10.9
Fluorescein, H20
5X10 -3
-
7-diethilamino-4-methylcoumazin, ethanol
1 × 10 -3 1 X10-2
25 250
9.4 83 66
Table 2 c(mole/•)
2 × 10 -2
U(kW)
150
~(mrad)
22
4 X 10-2 90 17.5
150
90
29
24
We found that the direction o f the light beam of the dye laser does not coincide with the X axis o f the resonator and deviates by an angle a in the direction o f propagation o f the exciting radiation (see fig. 1). 173
Volume 15, number 2
OPTICS COMMUNICATIONS
The angle a depends on the properties and the concentration of the dye, on the solvent and on the pumping power. The results of the measurements are given in tables 1 and 2, where c is the dye concentration in mole/~, k the absorption coefficient of the solution at the pumping wavelength (~ = 337.1 nm), ot the deviation of the dye laser beam from the resonator X axis, and U the peak pumping power. (Table 2 presents the data for the dye Rhodamine 6G.) The observed effect indicates that the pumping radiation induces a refractive index gradient in the Z direction. Further investigations showed that the deviation of the laser beam from the optical axis is not caused by the non-parallellity of the cuvette walls. The refractive index gradient in the excited dye may be ascribed to the following causes: 1. The temperature gradient produced by the exponential decrease of the pumping intensity and the heating effect with depth of the solution.
174
October 1975
2. Shock waves produced by the pumping pulse in the zone of generation. 3. The population of the excited state decreasing with the depth of the solution, having a maximum at Z = 0, while the population of the ground state shows an inverse change. Proceeding further in the direction of the Z axis the refractive index of the solution depends linearly on the concentration of the excited states, therefore the changes in the population of the ground and the excited states with the depth of the solution may lead to an increase of the refractive index in the Z direction Further investigations are necessary for a rigorous quantitative analysis of the observed effect.
References [1] G.A. Abakumov, M.A. Kasimdjanov, V.P. Protasov, A.P. Simonov, V.V. Fadeev and P.B. Khokhlov, Zhur. Prikl. Spektr. 15 (1971) 415.