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Broadband tuning of dye laser frequency using electrochemical reactions
Volume 23, number 1
OPTICS COMMUNICATIONS
October 1977
BROADBAND TUNING OF DYE LASER FREQUENCY USING ELECTROCHEMICAL REACTIONS V.A. ZHIVNOV, l.Yu. RUMYANTSEV, V.I. TOMIN, A.N RUBINOV Instttute of Phystcs. Academy of Sciences, USSR, Mtnsk Recewed 16 February 1976 Rewsed manuscript recewed 22 March 1977
A new way of dye laser frequency tuning which does not need the dye solution change is suggested The method is based on the use of electrochemical reactmns m an orgame dye solutmn. The electrochemical tuning of 4-methylumbelhferon solutmn as an actwe medium is achieved experimentally. The shift of the dye laser spectra of 80 nm (from 408 up to 484 nm) under the current transmission via an active medium IS obtained
The most important advantage of dye lasers is connected with their abdlty to a stimulated emission m any part of the broad spectral regmn of 3 4 0 - 1 2 0 0 nm. As the laser emission spectrum o f dye solution Ires w~thm the limits of its luminescence bands, ~t is necessary to change the solution for lasmg in another spectral region [1,2]. In the present paper a new way o f dye broadband laser frequency tuning which does not need the dye solution change Is suggested. The method zs based on the use o f electrochemical reactions m an organic dye soluuon. It is known that the transmlssmn o f electrical current through an organic dye solution may lead to the production of dye anion- and cation-radicals on the electrodes. The radicals diffuse into the bulk o f the solution and can participate in different chemical reactions. The processes are considered by several authors because of the problems o f an electrochemical excltatmn of dye luminescence and sumulated emlssmn [3-5]. In ttus paper we focus our attention on the potentmlmes o f electrochemical changing m dye solution spectral properties and its use for dye laser frequency tuning. In the experiments a 1.5 X 2.0 X 2.5 cm dye cell with two metallic wire electrodes inserted m it was used (see the top o f fig. 1). A dc voltage up to 10 V was apphed to the electrodes, and so a fast polarity change has been provaded.
Some characteristics of the absorpuon and luminescence spectra for three dyes are presented in table 1 In all cases the electrolysis products are seen to have mamma in the absorpnon and luminescence spectra which strongly differ from those in the mitml solution. It ~s necessary to underline that the fluorescence quantum yield of the electrolysis products can be higher than that of the mmal molecules (see table 1). The absorption and luminescence spectra of the neutral molecules are shown, for example, m fig. 1. The lumines-
I {ab
.
2 .
Wlum.
:m I
( arbzt, urn.)
1,2
%
0,9
\ \
i
0,6
% \
\\
0,3
•
I \
J
O! 270
310
350
IIIU
390
430
470
.
510
,
~.
~nm
Fxg. 1 AbsorpUon and luminescence spectra of the neutral molecules (sohd hnes) and the 4-methylumbelhpheron electrochemmal reaction products spectra (dotted line)
33
Volume 23, number 1
OPTICS COMMUNICATIONS
October 1977
Table 1 Spectral characteristics of the dyes and thmr electrolysis products on the cathode xabs (nm)
xlum (nm)
0 5
322 365
390 455
22
0 2
322 365
385 455
113
N, N-dmlethylformamide (C3H7NO)
0 10
520
415 550
2.15
ethanol (C2HsOH)
0 10
335
395 435
2 25
NN
The medmm under investigation
Solvent
1
4-MU
N, N-dlinethylformamade (C3H7NO) methanol (Ctt3OH)
2.
3
Fluoresceln
Pyren
Voltage (V)
r~m/no
V is the potential of the cathode, Z.abs, Xturn are the wavelengths of absorption and luminescence maxima rn the near-cathode region in the solutrons, rim~no is the quantum ymld of the electrolysis products relative to their aqueous solutmn The absorption spectra were recorded by a SP-800 spectrophotometer and the luminescence spectra by a Fica-50 spectrofluorometer
cence spectra are obtained by the excitation of a solution with ultraviolet radiation Fig. 1 shows the productIon of a luminescent species with the maximum of radiation shifted into the red region by 45 nm The absorption spectra of 4-methylumbelhferon (4-MU) electrochemical products are shifted by 43 nm The spectra of electrolysis products turned out to be identical to those of 4-MU anion form produced In a chemical way [6]. These data and voltamperographIc lnvestxgatlon results let us conclude that electrochemical process xn 4-MU solution leads to the production of dye anions. The dynamics of dye concentration increase in the near electrode region was investigated For this purpose the solution near the electrode was excited by the mercury lamp and luminescence of the electrolysis products was filtered and registered over definite time intervals (fig 2). Fig 3 represents the experimental dependence of the average cloud radius of 4-MU anion-radicals on the electric current l ransmIssion time. The cloud radius xs seen to be about 2 mm in 60 s. The electrochemical reactions of dyes can be used for tuning of a laser spectrum if the concentration of their luminescence products will be statable for lasIng We have found that for the dyes listed In table 1 it is possible to keep the concentration of electrochemical reaction products high enough for lasmg In a very large 34
region (several mm) near the electrode. We achieved electrochemmal tumng of dye laser spectra experimentally using 4-MU as an active medium The excitation was made by the second harmonic of a Q-switched 2 MW ruby laser. A transverse geometry of pumping was used. The dye laser resonator consisted of two mirrors with reflectivmes of 0.99 and 0.5. The full rectangles an fig. 1 denote the position of the laslng region for neutral and anion forms of 4-methylumbelllferon. The dye laser spectra registered with the help of a DC-13 grating spectrograph (resolution is 0 2 n m / m m ) are shown in fig. 4. As is seen from fig. 4 the current transmission via the solution under lnvestigatmn leads to the shift of dye laser spectra of 80 nm {from 408 up to 484 nm). It is possible to obtain the dye laser emission In any part of this spectral region by changing the voltage applied to the electrodes. This leads to change m proportion between the concentrations of neutral and amon forms and hence to laser frequency tuning It is known that a few dyes are required to cover this region by usual way. One of the important advantages of the electrochemical tuning IS its reversibility. The reversible reaction on transformation of the anion-radical into the neutral molecules takes place near the cathode after
Volume 23, number 1
OPTICS COMMUNICATIONS
October 1977
/0__~
~-'0
.0 /
2
o/
/
i
O/
i
i
,
.
J
Fig 3 Experimental dependence of the mean cloud radius of the 4-methylumbelhpheron anion-radicals on the elecmc current transmission time
Fig. 4 The methylumbelhpheron solution generation spectra a) before tile electric current transmission, b) during the electric current transmission changing the current polarity. As a result o f this reaction the dye laser s p e c t r u m does go back Into the blue regmn. Usually the electrochemical reactions on the electrode are under the &ffuslon control, and the tuning time o f the laser is d e t e r m m e d by the dimension l o f the active volume t ~ 12/6D,
where D is the diffusion coefficient. F r o m the expression follows that the value o f t is 2 × 10 - 2 s for D ~ 10 - 5 cm2/s and the dimension o f the active volume is ~ 10 3 cm. The value o f t can decrease up to Fig. 2 Photograph of the near-cathode region during the 4methylumbelhpheron solution electrolysis (electrode diameter is 0.5 ram) 35
October 1977
OPTICS COMMUNICATIONS
Volume 23, number 1
L I
|
I
I
Fig. 5. Photograph of the mare reversible tuning of laser emission spectra of Escuhn In ethanol. 1 is the basic solution, 2 represents the solution 20 s after the voltage was supphed, 3 represents the solution 15 s after the polarity was reversed
10 - 3 s b y a d d i n g s u p p o r t i n g e l e c t r o l y t e s t o the solutions. T h e m e t h o d s h o w s a n e w simple way for t h e electrical b r o a d b a n d t u n i n g o f d y e lasers.
References [ 1] B.I. Stepanov and A.N Rudmov, Usp. FLz Nauk. 95 (1968) 45
36
[2] Dye lasers, ed. F P Schafer (Springer Verlag, Berlin, Heidelberg, N Y , 1973). [3] C P. Keszthelyl, J Electrochem Soc 120 (1973) 39 [4] R M Measures, Appl Opt 13 (1974)1121 [5] R M Measures, Appl. Opt 14 (1975) 909 [6] A Dlenes, C.V. Shank and R.L. Kohn, IEEE J Quant Electron QE-9 (1973) 833.
OPTICS COMMUNICATIONS
October 1977
BROADBAND TUNING OF DYE LASER FREQUENCY USING ELECTROCHEMICAL REACTIONS V.A. ZHIVNOV, l.Yu. RUMYANTSEV, V.I. TOMIN, A.N RUBINOV Instttute of Phystcs. Academy of Sciences, USSR, Mtnsk Recewed 16 February 1976 Rewsed manuscript recewed 22 March 1977
A new way of dye laser frequency tuning which does not need the dye solution change is suggested The method is based on the use of electrochemical reactmns m an orgame dye solutmn. The electrochemical tuning of 4-methylumbelhferon solutmn as an actwe medium is achieved experimentally. The shift of the dye laser spectra of 80 nm (from 408 up to 484 nm) under the current transmission via an active medium IS obtained
The most important advantage of dye lasers is connected with their abdlty to a stimulated emission m any part of the broad spectral regmn of 3 4 0 - 1 2 0 0 nm. As the laser emission spectrum o f dye solution Ires w~thm the limits of its luminescence bands, ~t is necessary to change the solution for lasmg in another spectral region [1,2]. In the present paper a new way o f dye broadband laser frequency tuning which does not need the dye solution change Is suggested. The method zs based on the use o f electrochemical reactions m an organic dye soluuon. It is known that the transmlssmn o f electrical current through an organic dye solution may lead to the production of dye anion- and cation-radicals on the electrodes. The radicals diffuse into the bulk o f the solution and can participate in different chemical reactions. The processes are considered by several authors because of the problems o f an electrochemical excltatmn of dye luminescence and sumulated emlssmn [3-5]. In ttus paper we focus our attention on the potentmlmes o f electrochemical changing m dye solution spectral properties and its use for dye laser frequency tuning. In the experiments a 1.5 X 2.0 X 2.5 cm dye cell with two metallic wire electrodes inserted m it was used (see the top o f fig. 1). A dc voltage up to 10 V was apphed to the electrodes, and so a fast polarity change has been provaded.
Some characteristics of the absorpuon and luminescence spectra for three dyes are presented in table 1 In all cases the electrolysis products are seen to have mamma in the absorpnon and luminescence spectra which strongly differ from those in the mitml solution. It ~s necessary to underline that the fluorescence quantum yield of the electrolysis products can be higher than that of the mmal molecules (see table 1). The absorption and luminescence spectra of the neutral molecules are shown, for example, m fig. 1. The lumines-
I {ab
.
2 .
Wlum.
:m I
( arbzt, urn.)
1,2
%
0,9
\ \
i
0,6
% \
\\
0,3
•
I \
J
O! 270
310
350
IIIU
390
430
470
.
510
,
~.
~nm
Fxg. 1 AbsorpUon and luminescence spectra of the neutral molecules (sohd hnes) and the 4-methylumbelhpheron electrochemmal reaction products spectra (dotted line)
33
Volume 23, number 1
OPTICS COMMUNICATIONS
October 1977
Table 1 Spectral characteristics of the dyes and thmr electrolysis products on the cathode xabs (nm)
xlum (nm)
0 5
322 365
390 455
22
0 2
322 365
385 455
113
N, N-dmlethylformamide (C3H7NO)
0 10
520
415 550
2.15
ethanol (C2HsOH)
0 10
335
395 435
2 25
NN
The medmm under investigation
Solvent
1
4-MU
N, N-dlinethylformamade (C3H7NO) methanol (Ctt3OH)
2.
3
Fluoresceln
Pyren
Voltage (V)
r~m/no
V is the potential of the cathode, Z.abs, Xturn are the wavelengths of absorption and luminescence maxima rn the near-cathode region in the solutrons, rim~no is the quantum ymld of the electrolysis products relative to their aqueous solutmn The absorption spectra were recorded by a SP-800 spectrophotometer and the luminescence spectra by a Fica-50 spectrofluorometer
cence spectra are obtained by the excitation of a solution with ultraviolet radiation Fig. 1 shows the productIon of a luminescent species with the maximum of radiation shifted into the red region by 45 nm The absorption spectra of 4-methylumbelhferon (4-MU) electrochemical products are shifted by 43 nm The spectra of electrolysis products turned out to be identical to those of 4-MU anion form produced In a chemical way [6]. These data and voltamperographIc lnvestxgatlon results let us conclude that electrochemical process xn 4-MU solution leads to the production of dye anions. The dynamics of dye concentration increase in the near electrode region was investigated For this purpose the solution near the electrode was excited by the mercury lamp and luminescence of the electrolysis products was filtered and registered over definite time intervals (fig 2). Fig 3 represents the experimental dependence of the average cloud radius of 4-MU anion-radicals on the electric current l ransmIssion time. The cloud radius xs seen to be about 2 mm in 60 s. The electrochemical reactions of dyes can be used for tuning of a laser spectrum if the concentration of their luminescence products will be statable for lasIng We have found that for the dyes listed In table 1 it is possible to keep the concentration of electrochemical reaction products high enough for lasmg In a very large 34
region (several mm) near the electrode. We achieved electrochemmal tumng of dye laser spectra experimentally using 4-MU as an active medium The excitation was made by the second harmonic of a Q-switched 2 MW ruby laser. A transverse geometry of pumping was used. The dye laser resonator consisted of two mirrors with reflectivmes of 0.99 and 0.5. The full rectangles an fig. 1 denote the position of the laslng region for neutral and anion forms of 4-methylumbelllferon. The dye laser spectra registered with the help of a DC-13 grating spectrograph (resolution is 0 2 n m / m m ) are shown in fig. 4. As is seen from fig. 4 the current transmission via the solution under lnvestigatmn leads to the shift of dye laser spectra of 80 nm {from 408 up to 484 nm). It is possible to obtain the dye laser emission In any part of this spectral region by changing the voltage applied to the electrodes. This leads to change m proportion between the concentrations of neutral and amon forms and hence to laser frequency tuning It is known that a few dyes are required to cover this region by usual way. One of the important advantages of the electrochemical tuning IS its reversibility. The reversible reaction on transformation of the anion-radical into the neutral molecules takes place near the cathode after
Volume 23, number 1
OPTICS COMMUNICATIONS
October 1977
/0__~
~-'0
.0 /
2
o/
/
i
O/
i
i
,
.
J
Fig 3 Experimental dependence of the mean cloud radius of the 4-methylumbelhpheron anion-radicals on the elecmc current transmission time
Fig. 4 The methylumbelhpheron solution generation spectra a) before tile electric current transmission, b) during the electric current transmission changing the current polarity. As a result o f this reaction the dye laser s p e c t r u m does go back Into the blue regmn. Usually the electrochemical reactions on the electrode are under the &ffuslon control, and the tuning time o f the laser is d e t e r m m e d by the dimension l o f the active volume t ~ 12/6D,
where D is the diffusion coefficient. F r o m the expression follows that the value o f t is 2 × 10 - 2 s for D ~ 10 - 5 cm2/s and the dimension o f the active volume is ~ 10 3 cm. The value o f t can decrease up to Fig. 2 Photograph of the near-cathode region during the 4methylumbelhpheron solution electrolysis (electrode diameter is 0.5 ram) 35
October 1977
OPTICS COMMUNICATIONS
Volume 23, number 1
L I
|
I
I
Fig. 5. Photograph of the mare reversible tuning of laser emission spectra of Escuhn In ethanol. 1 is the basic solution, 2 represents the solution 20 s after the voltage was supphed, 3 represents the solution 15 s after the polarity was reversed
10 - 3 s b y a d d i n g s u p p o r t i n g e l e c t r o l y t e s t o the solutions. T h e m e t h o d s h o w s a n e w simple way for t h e electrical b r o a d b a n d t u n i n g o f d y e lasers.
References [ 1] B.I. Stepanov and A.N Rudmov, Usp. FLz Nauk. 95 (1968) 45
36
[2] Dye lasers, ed. F P Schafer (Springer Verlag, Berlin, Heidelberg, N Y , 1973). [3] C P. Keszthelyl, J Electrochem Soc 120 (1973) 39 [4] R M Measures, Appl Opt 13 (1974)1121 [5] R M Measures, Appl. Opt 14 (1975) 909 [6] A Dlenes, C.V. Shank and R.L. Kohn, IEEE J Quant Electron QE-9 (1973) 833.