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High-power dye laser in the near infrared
Volume
16, number
3
RlarchI Y7h
OPTIC’S COMMUNICATIONS
HIGH-POWER DYE LASER IN THE NEAR INFRARED
Received
28 Novcmhcr
I975
A tunable ivavelenpth, laser beam of very high qxctral luminance in the near infrared IS obtained by amplification 01 ,t monochromatic laser tine etnitted by a tunable dye oscillator. Optical pumping of the oscillator and the four-stage amphticl is effected by a giant pulse ruby laser. The energq obtained with a solution of 3.3’ dimethyl 2.2’ o\atricarhocyaninc iodide (D.O.T.C.) in dimethyl rulfoxyde is 1 J at 7699 A. The laser pulse of spectral width 4h = 0.065 4 is cmittcd at a ratt 01 0 I 111.The half-peak pulse duration is 15 nl.
The oscillator
Excitation from the ground of the atmospheric potassiutn D, line 7698.968 at an altitude of about 90 km so as to observe
the resonance
light requires
shown a
powerful light source of small spectral width, stable in wavelength and with a small beam spread. These recluirements tunable
led us to design a system
laser oscillator
fier. This technique
followed
is efficient
with a low power
by an energy
ampli-
both with flash pump-
and four-stage
the atnplifying stages by use of beam splitters ferent reflectivities (high-energy multidielectric
dow for pumping. angle. The thickness
(tluorescence
beam
of ditcoa-
ings). Each stage consists of a duralumin cell with two windows for passage of the laser beam and a side win-
[3--S]. The plurality of the amplifying stages makes it possible to excite each stage with an optimum flux auto-stimulation
used a~-c
(2.8 J, 15 ns at half peak; 12 mm diameter: rep. rate 0.1 Hz. vertical linear polarisation) is distributed ovet
ing [ I,?] and with giant pulse, ruby laser pumping
limiting
amplifiet-
in fig. I The giant pulse, ruby excitation
The cells are tilted
at Brewstzt-‘s
of the cell is such that the win-
amplification)
and parasite laser etnission between cell walls. We give here performances obtained when using ruby laser excitation. LB
A4
L7
A3
Lb
L5
A2
Al
L4
I:&. 1. Experimental set-up. I>: oscillator dye cell; a: diaphragm; PI:: Fabry-Perot etalon; MI: Mirror with mum reflection coefficient: Mz: Out-put mirror; E2. expander; Al to &: amplifier stages; L-J to La: beam or mirror: L, : cylindrical leny.
310
Ml
0.8 mm maxiEl : beam splitter
Fig. 2. Absorption and fluorescence DMSO, (‘= I .s x 10-4 M/l.
spectra
of D.0.T.C‘.
in
Volume
16, number
OPTICS COMMUNICATIONS
3
l! 0.065A
7698.96
A
Fig. 3. Densitogram of the laser line obtained with the use of all 3 Fabry-Perot etalons (20 shots are superimposed).
dows are not opposite to each other and parasite laser action is thus avoided. The useful length of amplification is 1.2 cm. Laser emission around 7700 8, was obtained with a solution of 3,3’ dimethyl 2,2’ oxatricarbocyanin iodide (D.O.T.C.) in dimethyl sulfoxyde Merck Uvasol. The D.O.T.C. comes from NipponKankoh-Shikiso Co and is used without purification. The concentration in the oscillator is 10V4 M/Q so as to center the wide laser band obtained without selector in the cavity at 7700 A. The amplifier concentration is 5 X 10V5 M/Q in order to obtain maximum energy. The absorption coefficient of D.O.T.C. at 6943 A is E = 180000I1M-f cm- 1 (fig. 2). The dye solution circulates through the cells by means of 2 teflon pumps and teflon tubing. The flow rate is about 8 cm3 s-l. The 2 mirrors of the oscillator are 63 cm apart and have reflection coefficients of 0.46 and > 0.99 at 7700 8. Spectral selection is made by means of 3 Fabry-Perot etalons of which the thicknesses and reflection coefficients at 7700 A are respectively: 12 pm and 0.8; 180 pm and 0.66, and 1.33 mm and 0.78. The 3 etalons as well as the output mirror are placed in a housing maintained at 32 + 0.1 “C in order to insure the wavelength stability of the laser line. A 0.8 mm diaphragm is placed in the cavity near the R,, mirror in order to reduce the number of transverse modes. A five-fold beam expander (f/40) placed in the cavity protects the coatings and reduces the beam divergence on the etalons. A second two-fold beam expander is placed at the oscillator outlet in order to adapt the beam geometrically to the amplifier. The different elements are aligned by means of a He-Ne laser when the cells are filled with pure solvent (D.O.T.C. absorbs strongly in the red).
March 1976
Table 1 Excitation and output energies of the different amplifying stages at 7698.96 A with Ah = 0.065 A. Wp: excitation energy for the stage; Wout: output energy; P: output peak power; n: energy conversion efficiency for the stage n = (Wout - Win)/ wP.
~~~~.
W out
wP
m
___
__
P
rl (MW) (%J) 0) ~~~ ~~~~ _~ ~_~~~ ~~
Oscill.
0.35
0.005
0.3
1.4
Ampli I
0.35
0.022
1.46
4.9
Ampli II
0.4
0.195
13
43
Ampli III
0.63
0.470
31.3
44
Ampli IV
1.12
1.oo
66 ~_~~ ~~__
47
Wavelength sweeping is done by rotation of the 3 etalons. The wavelength is first adjusted near the resonance line within +O.lS A by means of a grating spectrometer; it is centered at 7698.96 A within +0.013 A by means of a resonance oven containing potassium [6] which is placed behind the R,, mirror. The resonance light is detected by a photomultiplier and recorded on an oscilloscope. The spectral width was measured with a high-resolution spectrograph on photographic plate (fig. 3). Output energies are measured with a TRG 102 thermopile. With an excitation energy of 2.8 J at 6943 A the energy emitted around 7699 A is over 1 J. With no etalon in the cavity the spectral width of the amplified laser is 150 A. With etalons PFl , PF2 and PF3, laser line widths obtained are respectively 3,0.9 and 0.065 A. Energies obtained after each stage are given in table 1. The output pulse duration (15 ns) is the same as that of the exciting pulse. The beam spread after the amplifier is small: 60% of the energy is contained in 0.7 mrad. Photolysis of the D.O.T.C. solution is negligible after about 2000 shots under continuous operation: no energy loss was observed for 250 cm3 of solution in the oscillator and 500 cm3 in the amplifier. No wavelength drift was noted during 8 hours of continuous operation. The authors thank R. Astier, P. Flamant and G. Megie for fruitful discussions.
311
Volu~nc
16, number
3
OPTIC’S ~‘OMMUNICATIONS
Keferences [I]
P. I~larnant and Y.11. Meyer.
Appl. Phys. I.ett.
19 (1971
)
A91 I
,
.
,
P. I~larnant and Y.tI. Meyer, Opt. (‘ornmun.
7 (1973) 146. 7 (1974)
121C. Lath and G. Megic, 3. Phys. E. Sci. Instrum. 80.
312
14 1 K. I.rcy anti IL.Prudere, Opl. (‘u~nmun. 12 ( 1974) 98. 151 A.M. Bench-Bruevich, T.K. kuunwa end 1.0.
16, number
3
RlarchI Y7h
OPTIC’S COMMUNICATIONS
HIGH-POWER DYE LASER IN THE NEAR INFRARED
Received
28 Novcmhcr
I975
A tunable ivavelenpth, laser beam of very high qxctral luminance in the near infrared IS obtained by amplification 01 ,t monochromatic laser tine etnitted by a tunable dye oscillator. Optical pumping of the oscillator and the four-stage amphticl is effected by a giant pulse ruby laser. The energq obtained with a solution of 3.3’ dimethyl 2.2’ o\atricarhocyaninc iodide (D.O.T.C.) in dimethyl rulfoxyde is 1 J at 7699 A. The laser pulse of spectral width 4h = 0.065 4 is cmittcd at a ratt 01 0 I 111.The half-peak pulse duration is 15 nl.
The oscillator
Excitation from the ground of the atmospheric potassiutn D, line 7698.968 at an altitude of about 90 km so as to observe
the resonance
light requires
shown a
powerful light source of small spectral width, stable in wavelength and with a small beam spread. These recluirements tunable
led us to design a system
laser oscillator
fier. This technique
followed
is efficient
with a low power
by an energy
ampli-
both with flash pump-
and four-stage
the atnplifying stages by use of beam splitters ferent reflectivities (high-energy multidielectric
dow for pumping. angle. The thickness
(tluorescence
beam
of ditcoa-
ings). Each stage consists of a duralumin cell with two windows for passage of the laser beam and a side win-
[3--S]. The plurality of the amplifying stages makes it possible to excite each stage with an optimum flux auto-stimulation
used a~-c
(2.8 J, 15 ns at half peak; 12 mm diameter: rep. rate 0.1 Hz. vertical linear polarisation) is distributed ovet
ing [ I,?] and with giant pulse, ruby laser pumping
limiting
amplifiet-
in fig. I The giant pulse, ruby excitation
The cells are tilted
at Brewstzt-‘s
of the cell is such that the win-
amplification)
and parasite laser etnission between cell walls. We give here performances obtained when using ruby laser excitation. LB
A4
L7
A3
Lb
L5
A2
Al
L4
I:&. 1. Experimental set-up. I>: oscillator dye cell; a: diaphragm; PI:: Fabry-Perot etalon; MI: Mirror with mum reflection coefficient: Mz: Out-put mirror; E2. expander; Al to &: amplifier stages; L-J to La: beam or mirror: L, : cylindrical leny.
310
Ml
0.8 mm maxiEl : beam splitter
Fig. 2. Absorption and fluorescence DMSO, (‘= I .s x 10-4 M/l.
spectra
of D.0.T.C‘.
in
Volume
16, number
OPTICS COMMUNICATIONS
3
l! 0.065A
7698.96
A
Fig. 3. Densitogram of the laser line obtained with the use of all 3 Fabry-Perot etalons (20 shots are superimposed).
dows are not opposite to each other and parasite laser action is thus avoided. The useful length of amplification is 1.2 cm. Laser emission around 7700 8, was obtained with a solution of 3,3’ dimethyl 2,2’ oxatricarbocyanin iodide (D.O.T.C.) in dimethyl sulfoxyde Merck Uvasol. The D.O.T.C. comes from NipponKankoh-Shikiso Co and is used without purification. The concentration in the oscillator is 10V4 M/Q so as to center the wide laser band obtained without selector in the cavity at 7700 A. The amplifier concentration is 5 X 10V5 M/Q in order to obtain maximum energy. The absorption coefficient of D.O.T.C. at 6943 A is E = 180000I1M-f cm- 1 (fig. 2). The dye solution circulates through the cells by means of 2 teflon pumps and teflon tubing. The flow rate is about 8 cm3 s-l. The 2 mirrors of the oscillator are 63 cm apart and have reflection coefficients of 0.46 and > 0.99 at 7700 8. Spectral selection is made by means of 3 Fabry-Perot etalons of which the thicknesses and reflection coefficients at 7700 A are respectively: 12 pm and 0.8; 180 pm and 0.66, and 1.33 mm and 0.78. The 3 etalons as well as the output mirror are placed in a housing maintained at 32 + 0.1 “C in order to insure the wavelength stability of the laser line. A 0.8 mm diaphragm is placed in the cavity near the R,, mirror in order to reduce the number of transverse modes. A five-fold beam expander (f/40) placed in the cavity protects the coatings and reduces the beam divergence on the etalons. A second two-fold beam expander is placed at the oscillator outlet in order to adapt the beam geometrically to the amplifier. The different elements are aligned by means of a He-Ne laser when the cells are filled with pure solvent (D.O.T.C. absorbs strongly in the red).
March 1976
Table 1 Excitation and output energies of the different amplifying stages at 7698.96 A with Ah = 0.065 A. Wp: excitation energy for the stage; Wout: output energy; P: output peak power; n: energy conversion efficiency for the stage n = (Wout - Win)/ wP.
~~~~.
W out
wP
m
___
__
P
rl (MW) (%J) 0) ~~~ ~~~~ _~ ~_~~~ ~~
Oscill.
0.35
0.005
0.3
1.4
Ampli I
0.35
0.022
1.46
4.9
Ampli II
0.4
0.195
13
43
Ampli III
0.63
0.470
31.3
44
Ampli IV
1.12
1.oo
66 ~_~~ ~~__
47
Wavelength sweeping is done by rotation of the 3 etalons. The wavelength is first adjusted near the resonance line within +O.lS A by means of a grating spectrometer; it is centered at 7698.96 A within +0.013 A by means of a resonance oven containing potassium [6] which is placed behind the R,, mirror. The resonance light is detected by a photomultiplier and recorded on an oscilloscope. The spectral width was measured with a high-resolution spectrograph on photographic plate (fig. 3). Output energies are measured with a TRG 102 thermopile. With an excitation energy of 2.8 J at 6943 A the energy emitted around 7699 A is over 1 J. With no etalon in the cavity the spectral width of the amplified laser is 150 A. With etalons PFl , PF2 and PF3, laser line widths obtained are respectively 3,0.9 and 0.065 A. Energies obtained after each stage are given in table 1. The output pulse duration (15 ns) is the same as that of the exciting pulse. The beam spread after the amplifier is small: 60% of the energy is contained in 0.7 mrad. Photolysis of the D.O.T.C. solution is negligible after about 2000 shots under continuous operation: no energy loss was observed for 250 cm3 of solution in the oscillator and 500 cm3 in the amplifier. No wavelength drift was noted during 8 hours of continuous operation. The authors thank R. Astier, P. Flamant and G. Megie for fruitful discussions.
311
Volu~nc
16, number
3
OPTIC’S ~‘OMMUNICATIONS
Keferences [I]
P. I~larnant and Y.11. Meyer.
Appl. Phys. I.ett.
19 (1971
)
A91 I
,
.
,
P. I~larnant and Y.tI. Meyer, Opt. (‘ornmun.
7 (1973) 146. 7 (1974)
121C. Lath and G. Megic, 3. Phys. E. Sci. Instrum. 80.
312
14 1 K. I.rcy anti IL.Prudere, Opl. (‘u~nmun. 12 ( 1974) 98. 151 A.M. Bench-Bruevich, T.K. kuunwa end 1.0.