- Email: [email protected]
High efficiency superradiant traveling-wave dye laser
Volume
3, number 5
HIGH
OPTICS COMMUNICATIONS
EFFICIENCY
SUPERRADIANT
Laboratoire
July 1971
TRAVELING-WAVE
S. L. CHIN and G. BEDARD d’optique et Hyperfrlquences, D&?partement lJniversit& Laval, Q&bee, Canada Received
DYE
LASER
*
de Physique,
1 June 1971
High-efficiency (> 40%) superradiant traveling-wave rhodamine 6G dye emission has been observed using a dye cell pumped transversely by the second harmonic of a Q-switched Nd:glass laser. A wavelength shift with concentration was observed as well as an additional shift with pump power at a fixed concentration.
tion. The length of the focal line was made greater than that of the dye cell to ensure a strong uniform pumping of the cell containing rhodamine 6G in ethanol solution at various concentrations. Intense superradiant emission (0.5 MW) was observed through the curved walls of the dye cell, in both transverse directions. The overall efficiency (total output superradiant radibation energy/ input pump radiation energy at 5300 A) was measured to be as high as 40%. Since the length of the pump radiation focal line was greater than that of the active gain region by about 1 mm, only part of the pump pulse was focused into the dye cell. Consequently, the efficiency is actually greater than 40%. The waveiength shift with concentration, usually observed in dye laser, was also observed
Observation of superradiant traveling-wave emission from dyes has recently been reported [l-3]. The purpose of the present paper is to report the observation of a high-efficiency (> 40%) transversely pumped superradiant rhodamine 6G traveling-wave dye laser emission. The pump radiation was the second harmonic ,of a Q-switched Nd:glass laser (fig. 1). The 5300A incident 2MW pulse was focused by a cylindrical lens (f= 10 cm) through one of the flat windows of a cylindrical dye cell (20 mm in diameter by 10 mm thickness). The pump radiation focal line was located in the vicinity of the front window of the cell, but at 2 mm below its central axis to prevent regenera* Work supported by the National Research
Council
of
Canada under grant no. C. N. R. A-5795.
TO
OSCILLOSCOPE
SUPERRADIANT EMISSION
5300
DYE CELL
BEAM
ii
SPLITTER
CYLINDRICAL
u SECOND HARMONIC
LENS
Q- SWITCHED Nd
= GLASS
USER
CRYSTAL SUPERRADIANT EMISSION
Fig. 1. Superradiant
traveling-wave
dye laser:
experimental
set-up. 299
Volume 3, number 5
OPTICS COMMUNICATIONS
July 1971
5710 -
5700 -
-l-H-
-I-
1
-7
I b z
5690-
d
+
$
t
5680 5690 WAVELENGTH
5;15 -7-65
e
(i,
Fig. 2. Concentration versus wavelength for rhodamine 6G. (fig. 2) in the present traveling-wave case. However, an additional wavelength shift-to-the-red of the center of the superradiant spectral band was also observed at a fixed concentration (low3 M) with increase in pump power (fig. 3). The shift was about 30 A per ten-fold increase in pump power. Such a wavelength shift-to-thered with pump power might be due to saturation effects in the focal line region. At low pump power, most of the energy of the pump pulse was strongly absorbed at the focal line gain region, as demonstrated by the observation of a rather small superradiant output diameter (measured as 2 mm at a distance of 15 cm in front of any of the output cell curved walls). The pump radiation diverging away from the focal line region was not intense enough to initiate superradiant traveling-wave emission elsewhere in the dye cell. As the pump power was increased, the superradiant-active gain region elongated, in the forward direction with respect to the incident pump pulse, as demonstrated by the observation of a 10 mm superradiant output diameter as measured at same distance away from the cell. Saturation of the pump radiation absorption in the focal line region occurred during the initial part of the pump pulse. The focal line region then became transparent to the remainder of the pump pulse, which was still intense enough to initiate super300
5670’ 0
0.5
1.0 PUMP
15 PEAK
2.0
2.5
3.0
POWER (Mw)
Fig. 3. Wavelength of the center of the spectral band for rhodamine 6G in ethanol (lo-3M) versus pump peak power. radiant traveling-wave emission from the diverging part of the gain region. However, as the pump beam diverges away from the focal line region, the flux is no more sufficient to saturate the dye molecules. The higher the pump peak power, the faster the saturation occurred in the focal region. Hence, more and more of the pump energy was transmitted in the region outside the focal region and was used to pump the dye molecules. The superradiant traveling-wave emission then came out in the longer wavelength, where the gain is higher, and the center of the spectral band was shifted to the red. The same saturation effects would account for the high efficiency of the superradiant emission.
REFERENCES [l] M. E. Mack, Appl. Phys. Letters 15 (1969) 166. [2] C. V. Shank, A. Dienes and W. T. Silfvast, Appl. Phys. Letters 17 (1970) 307. [3] P. Peretti and P. Ranson, Opt. Commun. 3 (1971) 63.
3, number 5
HIGH
OPTICS COMMUNICATIONS
EFFICIENCY
SUPERRADIANT
Laboratoire
July 1971
TRAVELING-WAVE
S. L. CHIN and G. BEDARD d’optique et Hyperfrlquences, D&?partement lJniversit& Laval, Q&bee, Canada Received
DYE
LASER
*
de Physique,
1 June 1971
High-efficiency (> 40%) superradiant traveling-wave rhodamine 6G dye emission has been observed using a dye cell pumped transversely by the second harmonic of a Q-switched Nd:glass laser. A wavelength shift with concentration was observed as well as an additional shift with pump power at a fixed concentration.
tion. The length of the focal line was made greater than that of the dye cell to ensure a strong uniform pumping of the cell containing rhodamine 6G in ethanol solution at various concentrations. Intense superradiant emission (0.5 MW) was observed through the curved walls of the dye cell, in both transverse directions. The overall efficiency (total output superradiant radibation energy/ input pump radiation energy at 5300 A) was measured to be as high as 40%. Since the length of the pump radiation focal line was greater than that of the active gain region by about 1 mm, only part of the pump pulse was focused into the dye cell. Consequently, the efficiency is actually greater than 40%. The waveiength shift with concentration, usually observed in dye laser, was also observed
Observation of superradiant traveling-wave emission from dyes has recently been reported [l-3]. The purpose of the present paper is to report the observation of a high-efficiency (> 40%) transversely pumped superradiant rhodamine 6G traveling-wave dye laser emission. The pump radiation was the second harmonic ,of a Q-switched Nd:glass laser (fig. 1). The 5300A incident 2MW pulse was focused by a cylindrical lens (f= 10 cm) through one of the flat windows of a cylindrical dye cell (20 mm in diameter by 10 mm thickness). The pump radiation focal line was located in the vicinity of the front window of the cell, but at 2 mm below its central axis to prevent regenera* Work supported by the National Research
Council
of
Canada under grant no. C. N. R. A-5795.
TO
OSCILLOSCOPE
SUPERRADIANT EMISSION
5300
DYE CELL
BEAM
ii
SPLITTER
CYLINDRICAL
u SECOND HARMONIC
LENS
Q- SWITCHED Nd
= GLASS
USER
CRYSTAL SUPERRADIANT EMISSION
Fig. 1. Superradiant
traveling-wave
dye laser:
experimental
set-up. 299
Volume 3, number 5
OPTICS COMMUNICATIONS
July 1971
5710 -
5700 -
-l-H-
-I-
1
-7
I b z
5690-
d
+
$
t
5680 5690 WAVELENGTH
5;15 -7-65
e
(i,
Fig. 2. Concentration versus wavelength for rhodamine 6G. (fig. 2) in the present traveling-wave case. However, an additional wavelength shift-to-the-red of the center of the superradiant spectral band was also observed at a fixed concentration (low3 M) with increase in pump power (fig. 3). The shift was about 30 A per ten-fold increase in pump power. Such a wavelength shift-to-thered with pump power might be due to saturation effects in the focal line region. At low pump power, most of the energy of the pump pulse was strongly absorbed at the focal line gain region, as demonstrated by the observation of a rather small superradiant output diameter (measured as 2 mm at a distance of 15 cm in front of any of the output cell curved walls). The pump radiation diverging away from the focal line region was not intense enough to initiate superradiant traveling-wave emission elsewhere in the dye cell. As the pump power was increased, the superradiant-active gain region elongated, in the forward direction with respect to the incident pump pulse, as demonstrated by the observation of a 10 mm superradiant output diameter as measured at same distance away from the cell. Saturation of the pump radiation absorption in the focal line region occurred during the initial part of the pump pulse. The focal line region then became transparent to the remainder of the pump pulse, which was still intense enough to initiate super300
5670’ 0
0.5
1.0 PUMP
15 PEAK
2.0
2.5
3.0
POWER (Mw)
Fig. 3. Wavelength of the center of the spectral band for rhodamine 6G in ethanol (lo-3M) versus pump peak power. radiant traveling-wave emission from the diverging part of the gain region. However, as the pump beam diverges away from the focal line region, the flux is no more sufficient to saturate the dye molecules. The higher the pump peak power, the faster the saturation occurred in the focal region. Hence, more and more of the pump energy was transmitted in the region outside the focal region and was used to pump the dye molecules. The superradiant traveling-wave emission then came out in the longer wavelength, where the gain is higher, and the center of the spectral band was shifted to the red. The same saturation effects would account for the high efficiency of the superradiant emission.
REFERENCES [l] M. E. Mack, Appl. Phys. Letters 15 (1969) 166. [2] C. V. Shank, A. Dienes and W. T. Silfvast, Appl. Phys. Letters 17 (1970) 307. [3] P. Peretti and P. Ranson, Opt. Commun. 3 (1971) 63.