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Photobleaching of rhodamin 6 G dye laser by flashlamp exciting
Volume 37A, number 3
PHYSICS LETTERS
22 November 1971
PHOTOBLEACHING OF RHODAMIN 6 G DYE BY FLASHLAMP EXCITING
LASER
J. W E B E R I. P h y s i k a l i s c h e s Institut d e r Technischen Universititt Berlin, Germany
Received 2 October 1971
Photobleaching of rhodamin 6 G dye laser by flashlamp-excitiag induces a decrease of the quantum yield and an increase of the threshold energy.
The e l e c t r i c a l t h r e s h o l d e n e r g y f o r f l a s h l a m p e x c i t a t i o n of r h o d a m i n 6 G l a s e r (2x 105 W / c m 3-) c o r r e s p o n d s to 6 x 103 W / c m 3 optical pump powe r d e n s i t y [1]. Under t h e s e conditions a b l e a c h i n g of the dye m o l e c u l e s is o b s e r v e d [2,3]. The p u r p o s e of the p r e s e n t p a p e r is to r e p o r t that the b l e a c h e d f o r m of the dye i n d i c e a d e c r e a s e of the quantum y i e l d by f l u o r e s c e n c e quenching and an i n c r e a s e in the t h r e s h o l d e n e r g y . A solution of r h o d a m i n 6 G m e t h a n o l o r w a t e r was c i r c u l a t e d by a p u m p s y s t e m . Oxygen o r CBH 8 w e r e u s e d fo r t r i p l e t quenching. In the c a s e of CsH 8 oxygen was r e m o v e d by bubbling N 2 through the r e s e r v o i r . Two plan m i r r o r s of 99% r e f l e c t a n c e f o r m e d the optical cavity. The b r e w s t e r angle dye c e l l was of q u a r t z o r Schott G 20 g l a s s of 4 m m i n n e r d i a m e t e r and a length of 80 mm. The dye was e x c i t e d with a l i n e a r xenon f l a s h l a m p . The dye was b l e a c h e d by e x c i t i n g a v o l u m e of 10 m l with pumplight p u l s e s of 1.2 m s e c FWHM and 1350 Ws e l e c t r i c a l e n e r g y . By the b l e a c h i n g the t r a n s m i s s i o n , the f l u o r e s c e n c e i n t e n s i t y and the t h r e s h o l d e n e r g y changes. The t r a n s m i s s i o n (~= 5300 AE) i n c r e a s e s with the n u m b e r of e x c i t i n g p u l s e s (fig. 1). F r o m the change in the t r a n s m i s s i o n , the e x c i t e d v o l u m e and the known c o n c e n t r a t i o n the n u m b e r of b l e a c h e d m o l e c u l e s w e r e c a l c u l a t e d (table 1). The b l e a c h i n g r a t e is dependent of the a b s o r b e d e n e r g y (fig. 1), the s o l v e n t and n e a r l y independent of the dye c o n c e n t r a t i o n (table 1). The
TrQnsrnission
15"
ethano~ in quo r tzcuvettl
I0
I j I L./~-
.,~.....--- - ' ~ ' ~ H20in G20cuvette ~
~.methanolinG20cuvette
Fig. 1 Normalized transmission versus the number of exciting pulses. Measured at ~ -- 5300 AE. s m a l l e s t b l e a c h i n g r a t e was obtained by e x c i t i n g without the UV light of the f l a s h l a m p by u si n g a dye c e l l of G 20 g l a s s . This g l a s s a b s o r b s the w a v e l e n g t h s s h o r t e r than 3500 AE. By e x c i t i n g with 80 p u l s e s the f l u o r e s c e n c e i n t e n s i t y J F changes f r o m 1.0 to 0.65 (fig. 2). T h i s d e c r e a s e of J F is not only p r o d u c e d by the d e c r e a s e of the c o n c e n t r a t i o n by bleaching. F o r the dilution of a 5× 10 -5 m o l a r solution with p u r e m e t h a n o l to 3X 10 -5 m o l a r , c o r r e s p o n d i n g to b l e a c h i n g of 10 ml in a q u a r t z cu v et t e with 80 p u l s e s , i n d u ces only a change of the i n t en si t y J F f r o m 1.0 to 0.9 (curve A, fig. 2). It is supposed that the d e c r e a s e of the f l u o r e s -
Table 1. Number of bleached molecules by exciting with 80 pulses. 16 x 1015 17 x l 0 -5 7 x 1015 2 x l015
cm -3 cm -3 cm -3 cm -3
with with with with
a a a a
5 x 10 -5 1 x l 0 -4 5 x 10-5 5 x 10 -5
tool mol tool tool
solution solution solution solution
in in in in
methanol ) methanol H20 methanol
1
quartz cuvette G 20 glass-cuvette
179
Volume 37A, number 3
1~HYSICS LETTERS
Fluorescence intensity JF
22 November 1971
2.0
02
1.0 curveA
~
::::::,:::::"'
0.8
0.6-
~
~
'
~
a
~o
t
a 60
methanoiinquartzcuvette
S _~ 1.5
02 methanol
1.0
A ,
I
a 20
D
~o
Fig. 2. Normalized fluorescence intensity J F v e r s u s the number of exciting pulses. Excited with )t = 5200 AE, m e a s u r e d at X = 5600 AE. cence intensity JF is produced by fluorescence q u e n c h i n g . F ~ r s t e r [4] d e s c r i b e d two p o s s i b i l i t i e s for fluorescence quenching. 1. T h e b l e a c h e d f o r m of t h e dye a n d t h e d y e m o l e c u l e s i n t e r a c t s o t h a t t h e e n e r g y of t h e e x cited dye molecule is transfered to the bleached f o r m of t h e dye. In t h i s c a s e t h e f l u o r e s c e n c e decay time will become shorter ('dynamic fluorescence quenching'). 2. T h e b l e a c h e d a n d u n b l e a c h e d d y e m o l e c u l e s form a molecule aggregate. This aggregate has the same absorption coefficient as an unbleached m o l e c u l e b u t t h e r e w i l l b e no f l u o r e s c e n c e . In this case the fluorescence decay time will be constant ('static fluorescence quenching'). T h e m e a s u r e d d e c a y t i m e ( r = 5.5X 1 0 - ' 9 s e c ) w a s i n d e p e n d e n t of b l e a c h i n g , s o it s e e m e d to b e a 'static fluorescence quenching'. B e c a u s e of t h i s f l u o r e s c e n c e q u e n c h i n g t h e q u a n t u m y i e l d b e c o m e s s m a l l e r a n d g i v e s r i s e to a n i n c r e a s e of t h e t h r e s h o l d e n e r g y . T o d e m o n s t r a t e t h e s t r o n g i n f l u e n c e of b l e a c h e d d y e o n t h e threshold energy the following experiment is m a d e . B l e a c h e d d y e i s a d d e d to a v o l u m e of 100 m l u n b l e a c h e d dye. T h e n t h e t h r e s h o l d i s i n c r e a s e d (fig. 3). T h i s t h r e s h o l d i n c r e a s i n g i s n o t
180
,
,
1
.
.
.
. 2' .0 .
.
3 bleached ' ' dy "0 [ml]
number of pulses
Fig. 3. Norma]ized threshold energy v e r s u s the volume of added bleached dye. Curve A: Pure methanol is added, 02 for triplettquenching. Curve B: C8H 8 for triplettquenching. Curve C: 02 for triplettquenching.
produced by a change of the concentration, because by adding pure methanol the threshold energy did not change (fig. 3, A). By neglecting thermal effects it is possible to calculate from the bleaching rate and the increase of the threshold energy the pulselength that can be obtained with an active volume of I ml. By using 0 2 as triplettquencher the laseremission should finish after t = 4 msec, by using C8H8 after l = 5 msec. By exciting without UV-light, the bleaching rate is smaller and therefore the pulselength should grow up to t = 40 - 50 msec. T h e a u t h o r w i s h e s to e x p r e s s h i s g r a t i t u d e f o r t h e d i s c u s s i o n s of t h e p r o b l e m w i t h P r o f e s s o r Boersch.
References [1] B. Snavely and F. P. Seh~lfer, Phys. L e t t e r s , VoI. 28A (1968) 728. [2] J. Weber, Z. angew. Phys. 31 (1971) Heft 1. [3] E. P. Ippen, C.V. Shank and A. Dienes, JEEQE (1971) p. 178-179. [4] H. Meier, Photoehemie der organischen Farbstoffe, (Springer Berlin, 1963).
PHYSICS LETTERS
22 November 1971
PHOTOBLEACHING OF RHODAMIN 6 G DYE BY FLASHLAMP EXCITING
LASER
J. W E B E R I. P h y s i k a l i s c h e s Institut d e r Technischen Universititt Berlin, Germany
Received 2 October 1971
Photobleaching of rhodamin 6 G dye laser by flashlamp-excitiag induces a decrease of the quantum yield and an increase of the threshold energy.
The e l e c t r i c a l t h r e s h o l d e n e r g y f o r f l a s h l a m p e x c i t a t i o n of r h o d a m i n 6 G l a s e r (2x 105 W / c m 3-) c o r r e s p o n d s to 6 x 103 W / c m 3 optical pump powe r d e n s i t y [1]. Under t h e s e conditions a b l e a c h i n g of the dye m o l e c u l e s is o b s e r v e d [2,3]. The p u r p o s e of the p r e s e n t p a p e r is to r e p o r t that the b l e a c h e d f o r m of the dye i n d i c e a d e c r e a s e of the quantum y i e l d by f l u o r e s c e n c e quenching and an i n c r e a s e in the t h r e s h o l d e n e r g y . A solution of r h o d a m i n 6 G m e t h a n o l o r w a t e r was c i r c u l a t e d by a p u m p s y s t e m . Oxygen o r CBH 8 w e r e u s e d fo r t r i p l e t quenching. In the c a s e of CsH 8 oxygen was r e m o v e d by bubbling N 2 through the r e s e r v o i r . Two plan m i r r o r s of 99% r e f l e c t a n c e f o r m e d the optical cavity. The b r e w s t e r angle dye c e l l was of q u a r t z o r Schott G 20 g l a s s of 4 m m i n n e r d i a m e t e r and a length of 80 mm. The dye was e x c i t e d with a l i n e a r xenon f l a s h l a m p . The dye was b l e a c h e d by e x c i t i n g a v o l u m e of 10 m l with pumplight p u l s e s of 1.2 m s e c FWHM and 1350 Ws e l e c t r i c a l e n e r g y . By the b l e a c h i n g the t r a n s m i s s i o n , the f l u o r e s c e n c e i n t e n s i t y and the t h r e s h o l d e n e r g y changes. The t r a n s m i s s i o n (~= 5300 AE) i n c r e a s e s with the n u m b e r of e x c i t i n g p u l s e s (fig. 1). F r o m the change in the t r a n s m i s s i o n , the e x c i t e d v o l u m e and the known c o n c e n t r a t i o n the n u m b e r of b l e a c h e d m o l e c u l e s w e r e c a l c u l a t e d (table 1). The b l e a c h i n g r a t e is dependent of the a b s o r b e d e n e r g y (fig. 1), the s o l v e n t and n e a r l y independent of the dye c o n c e n t r a t i o n (table 1). The
TrQnsrnission
15"
ethano~ in quo r tzcuvettl
I0
I j I L./~-
.,~.....--- - ' ~ ' ~ H20in G20cuvette ~
~.methanolinG20cuvette
Fig. 1 Normalized transmission versus the number of exciting pulses. Measured at ~ -- 5300 AE. s m a l l e s t b l e a c h i n g r a t e was obtained by e x c i t i n g without the UV light of the f l a s h l a m p by u si n g a dye c e l l of G 20 g l a s s . This g l a s s a b s o r b s the w a v e l e n g t h s s h o r t e r than 3500 AE. By e x c i t i n g with 80 p u l s e s the f l u o r e s c e n c e i n t e n s i t y J F changes f r o m 1.0 to 0.65 (fig. 2). T h i s d e c r e a s e of J F is not only p r o d u c e d by the d e c r e a s e of the c o n c e n t r a t i o n by bleaching. F o r the dilution of a 5× 10 -5 m o l a r solution with p u r e m e t h a n o l to 3X 10 -5 m o l a r , c o r r e s p o n d i n g to b l e a c h i n g of 10 ml in a q u a r t z cu v et t e with 80 p u l s e s , i n d u ces only a change of the i n t en si t y J F f r o m 1.0 to 0.9 (curve A, fig. 2). It is supposed that the d e c r e a s e of the f l u o r e s -
Table 1. Number of bleached molecules by exciting with 80 pulses. 16 x 1015 17 x l 0 -5 7 x 1015 2 x l015
cm -3 cm -3 cm -3 cm -3
with with with with
a a a a
5 x 10 -5 1 x l 0 -4 5 x 10-5 5 x 10 -5
tool mol tool tool
solution solution solution solution
in in in in
methanol ) methanol H20 methanol
1
quartz cuvette G 20 glass-cuvette
179
Volume 37A, number 3
1~HYSICS LETTERS
Fluorescence intensity JF
22 November 1971
2.0
02
1.0 curveA
~
::::::,:::::"'
0.8
0.6-
~
~
'
~
a
~o
t
a 60
methanoiinquartzcuvette
S _~ 1.5
02 methanol
1.0
A ,
I
a 20
D
~o
Fig. 2. Normalized fluorescence intensity J F v e r s u s the number of exciting pulses. Excited with )t = 5200 AE, m e a s u r e d at X = 5600 AE. cence intensity JF is produced by fluorescence q u e n c h i n g . F ~ r s t e r [4] d e s c r i b e d two p o s s i b i l i t i e s for fluorescence quenching. 1. T h e b l e a c h e d f o r m of t h e dye a n d t h e d y e m o l e c u l e s i n t e r a c t s o t h a t t h e e n e r g y of t h e e x cited dye molecule is transfered to the bleached f o r m of t h e dye. In t h i s c a s e t h e f l u o r e s c e n c e decay time will become shorter ('dynamic fluorescence quenching'). 2. T h e b l e a c h e d a n d u n b l e a c h e d d y e m o l e c u l e s form a molecule aggregate. This aggregate has the same absorption coefficient as an unbleached m o l e c u l e b u t t h e r e w i l l b e no f l u o r e s c e n c e . In this case the fluorescence decay time will be constant ('static fluorescence quenching'). T h e m e a s u r e d d e c a y t i m e ( r = 5.5X 1 0 - ' 9 s e c ) w a s i n d e p e n d e n t of b l e a c h i n g , s o it s e e m e d to b e a 'static fluorescence quenching'. B e c a u s e of t h i s f l u o r e s c e n c e q u e n c h i n g t h e q u a n t u m y i e l d b e c o m e s s m a l l e r a n d g i v e s r i s e to a n i n c r e a s e of t h e t h r e s h o l d e n e r g y . T o d e m o n s t r a t e t h e s t r o n g i n f l u e n c e of b l e a c h e d d y e o n t h e threshold energy the following experiment is m a d e . B l e a c h e d d y e i s a d d e d to a v o l u m e of 100 m l u n b l e a c h e d dye. T h e n t h e t h r e s h o l d i s i n c r e a s e d (fig. 3). T h i s t h r e s h o l d i n c r e a s i n g i s n o t
180
,
,
1
.
.
.
. 2' .0 .
.
3 bleached ' ' dy "0 [ml]
number of pulses
Fig. 3. Norma]ized threshold energy v e r s u s the volume of added bleached dye. Curve A: Pure methanol is added, 02 for triplettquenching. Curve B: C8H 8 for triplettquenching. Curve C: 02 for triplettquenching.
produced by a change of the concentration, because by adding pure methanol the threshold energy did not change (fig. 3, A). By neglecting thermal effects it is possible to calculate from the bleaching rate and the increase of the threshold energy the pulselength that can be obtained with an active volume of I ml. By using 0 2 as triplettquencher the laseremission should finish after t = 4 msec, by using C8H8 after l = 5 msec. By exciting without UV-light, the bleaching rate is smaller and therefore the pulselength should grow up to t = 40 - 50 msec. T h e a u t h o r w i s h e s to e x p r e s s h i s g r a t i t u d e f o r t h e d i s c u s s i o n s of t h e p r o b l e m w i t h P r o f e s s o r Boersch.
References [1] B. Snavely and F. P. Seh~lfer, Phys. L e t t e r s , VoI. 28A (1968) 728. [2] J. Weber, Z. angew. Phys. 31 (1971) Heft 1. [3] E. P. Ippen, C.V. Shank and A. Dienes, JEEQE (1971) p. 178-179. [4] H. Meier, Photoehemie der organischen Farbstoffe, (Springer Berlin, 1963).