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additive flame laser output spectra
Volume 77A, number 6
PHYSICS LETTERS
23 June 1980
EXJ’ERJMENTAL STUDY OF CS2/02/ADDITIVE FLAME LASER OUTPUT SPECTRA M. TRTICA and N. KONJEVIC Institute of Applied Physics, 11001 Beograd, P.O. Box 24, Yugoslavia Received 28 February 1980
This letter describes an experimental investigation of the spectral composition ofthe output of CS2 /02/N2 0 and CS2/02/C02 flame lasers with nondispersive optical cavity. CO-additive V-V exchange probabilities were used to explain spectral composition of the laser power output.
It has been pointed additives apart from total power output canout alsothat change the spectral distribution of the output power in CW transverse-flow CO chemical lasers [1]. In case of CO flame laser some authors reported details of CS 2/02/N2O multiline output spectra [2—4]but no attempt has been made to study output spectra in presence of other additives than N20. The aim of this paper is to report the comparative study of the spectral composition of the output spectra of free burning CS2/02/Additive flame laser with nondispersive optical cavity, The details of our CO flame laser have been described elsewhere [5] and only minimum details are given here for the sake of completeness. The burner which was used in this study was 36 cm long and 0.8 cm wide. The burner top consisted of a brass cylinder containing about 700 holes 1 mm in diameter, having a center-to-center spacing 1.5 mm. To stabilize flame a 36 mesh stainless steel screen was placed 3 mm above the burner top. Prior to arrival at the entrance part of the burner, oxygen and additives are premixed. The carbon bisulfide is added to the oxygen—additive mixture in front of the entrance to the burner where the pressure is low and fast mixing occurs. The burner was mounted on a pipe which extends through the bottorn of the housing into the vacuum chamber of the total volume of about 9 1. This chamber was connected to the root pump placed in series with two stage mechanical vacuum pump. The overall capacity
3/h. of vacuum about 170 m of a 5 m radius The laserpumps opticalwas cavity consisted of curvature total reflector of the gold coated metal type and one flat ZnSe partial reflector with the reflectivity of 98.5% at 5.3 pm. Total laser power output measurements were performed with Coherent radiation power meter Model 210. For spectroscopic studies of laser output spectra 0.5 m Jarrel-Ash scanning spectrometer was used with 80 pm slits and 74 lines/mm grating blazed for 5 pm. The laser beam was chopped at 600 Hz and detected with a piroelectric detector (Plessy, Model PSC 222) whose output was connected to a lock-in amplifier (PAR, Model 124A), and further to a strip chart recorder. Speed of spectra recording was 8000 A/mm. The wavelength was calibrated with HE-Ne laser at 3.39 pm in the 1st, 2nd and 3rd orders. For the comparative spectroscopic study of the laser output spectra additives N2O and CO2 were chosen. Spectra recordings were taken with the following flows of CS2, 02 and additives: CS2 = 1.8 mmoles/s 02
=
14.1 with N2O and 12.2 mmoles/s with CO2
N20 = 6.1—1L7 mmoles/s CO2
=
5.3—13.3 mmoles/s
Total pressure in the flame chamber varied between 16 and 19 rnbar with N2O and 14 and 17 mbar with CO2. 435
Volume 77A, number 6
23 June 1980
PHYSICS LETTERS
CS2 /02/N20 Irt
7—6
I
10-9
‘~~-
8-7
FLOW RATES: 02 = 14.1 mmoles•s’ CS2= 1.Bmmoles-s’
11-10
1 PRESSURE = 16 mbcir N2O~6.1mmoIess P -1W
0) -
9-8
tot
—
6-5 ‘—“-—S
0
0) — c—I
—~
.4
)D (~~1
~..
0)
)‘I
— (SI
CS
2/02/ CO~ 9-8 FLOW RATES: 0
10-9
Ø.~7
5.1
5.2
5.3
02 = 12.2 mmoles-s’ CS2= 1.8mmoIes.s~ C02= 5.3mmoles.s’ PRESSURE =l4mbcir P~0~ = 0.2 W
11-10
5.4
5.5
5.6
Fig. 1. Typical spectra recordings for CS2/02/N20 and CS2/02/C02 flame laser.
Typical set of spectra recordings is given in fig. 1. Since these spectra are going to be compared, the examples of spectra in fig. 1 are taken with similar flow rates of the additives. This is crucial since the variation of the additive flow rate may induce variations in the output spectrum as well [5]. In order to 436
compare lasing from various vibrational levels of CO, experimental data of laser output spectra, fig. 1, are given in another form, fig. 2. Here, total power output obtained at all transitions within a single vibrational transition is proportional to the length of a single line. Together with the spectral composition of the
Volume 77A, number 6
PHYSICS LETTERS
23 June 1980
On the basis of the comparison of V-V probability curves and spectral composition of the laser power
CO-N,O
output data, fig. 2, one can make following conclusions: (a) N20 has much larger V-V exchange proba-
10’
bifities and therefore it is more efficient additive and (b) CO2 is more spectrally selective additive in comparison with N2 0. First conclusion has been proven already in the early experiments [7,3]. As regards to the second conclusion it is clear from fig. 2 that spectral distribution curves of the laser power output can be related to the shape of V-V probability curves. Therefore, the effect of additives to the power output spectrum can be explained by the influence of the V-V transfer rates for additive CO collisions which vary considerably over the range of CO vibrational levels active in the laser. This changes the inversion ratio of various vibrational levels and hence gain coefficients which are responsible for the laser power output and its spectrum composition.
-
6
—
CO-CO~
5
-
i0
References 0
El]
2
I
-~
W.Q. Jeffers and C.E. Wiswail, J. Quant. Electron. QE-lO (1974) 860.
[2] H.S. Pifioff, S.K. Searles and N. Djeu, App!. Phys. Lett. 19 (1971) 9. and R.A. Carabetta, Appi. Phys. Lett. 22 [3] M.J. Linevsky
I
(1973) 288.
[4] K.D. Foster, G.H. Kimbeil and D.R. Sneiling, J. Quant. ______________________________________________ 1
2
3
4
5
6
7
8
Vibrational
Fig. 2.
Reduced
9
10
11
12
13
14
15
level V
Electron. QE-Il (1975) 253. [5] Z. Babarogié, N. Konjevié and M. Trtica, Rev. Sd Inst., to be published. [6] G. Hancock and LW.M. Smith, AppL Opt. 10 (1971)
V-V exchange probabilities for C0-N
20 and CO-CO2 [6] together with typical spectral composition of the output of CO flame laser. Experimental conditions are same as in fig. 1.
1827. [7] S.K. Searles and N. L~eu,Chem. Phys. Left. 12 (1971) 53~
laser power output in the same figure are given reduced CO-N20 and CO-CO2 V-V exchange probabilities [6].
437
PHYSICS LETTERS
23 June 1980
EXJ’ERJMENTAL STUDY OF CS2/02/ADDITIVE FLAME LASER OUTPUT SPECTRA M. TRTICA and N. KONJEVIC Institute of Applied Physics, 11001 Beograd, P.O. Box 24, Yugoslavia Received 28 February 1980
This letter describes an experimental investigation of the spectral composition ofthe output of CS2 /02/N2 0 and CS2/02/C02 flame lasers with nondispersive optical cavity. CO-additive V-V exchange probabilities were used to explain spectral composition of the laser power output.
It has been pointed additives apart from total power output canout alsothat change the spectral distribution of the output power in CW transverse-flow CO chemical lasers [1]. In case of CO flame laser some authors reported details of CS 2/02/N2O multiline output spectra [2—4]but no attempt has been made to study output spectra in presence of other additives than N20. The aim of this paper is to report the comparative study of the spectral composition of the output spectra of free burning CS2/02/Additive flame laser with nondispersive optical cavity, The details of our CO flame laser have been described elsewhere [5] and only minimum details are given here for the sake of completeness. The burner which was used in this study was 36 cm long and 0.8 cm wide. The burner top consisted of a brass cylinder containing about 700 holes 1 mm in diameter, having a center-to-center spacing 1.5 mm. To stabilize flame a 36 mesh stainless steel screen was placed 3 mm above the burner top. Prior to arrival at the entrance part of the burner, oxygen and additives are premixed. The carbon bisulfide is added to the oxygen—additive mixture in front of the entrance to the burner where the pressure is low and fast mixing occurs. The burner was mounted on a pipe which extends through the bottorn of the housing into the vacuum chamber of the total volume of about 9 1. This chamber was connected to the root pump placed in series with two stage mechanical vacuum pump. The overall capacity
3/h. of vacuum about 170 m of a 5 m radius The laserpumps opticalwas cavity consisted of curvature total reflector of the gold coated metal type and one flat ZnSe partial reflector with the reflectivity of 98.5% at 5.3 pm. Total laser power output measurements were performed with Coherent radiation power meter Model 210. For spectroscopic studies of laser output spectra 0.5 m Jarrel-Ash scanning spectrometer was used with 80 pm slits and 74 lines/mm grating blazed for 5 pm. The laser beam was chopped at 600 Hz and detected with a piroelectric detector (Plessy, Model PSC 222) whose output was connected to a lock-in amplifier (PAR, Model 124A), and further to a strip chart recorder. Speed of spectra recording was 8000 A/mm. The wavelength was calibrated with HE-Ne laser at 3.39 pm in the 1st, 2nd and 3rd orders. For the comparative spectroscopic study of the laser output spectra additives N2O and CO2 were chosen. Spectra recordings were taken with the following flows of CS2, 02 and additives: CS2 = 1.8 mmoles/s 02
=
14.1 with N2O and 12.2 mmoles/s with CO2
N20 = 6.1—1L7 mmoles/s CO2
=
5.3—13.3 mmoles/s
Total pressure in the flame chamber varied between 16 and 19 rnbar with N2O and 14 and 17 mbar with CO2. 435
Volume 77A, number 6
23 June 1980
PHYSICS LETTERS
CS2 /02/N20 Irt
7—6
I
10-9
‘~~-
8-7
FLOW RATES: 02 = 14.1 mmoles•s’ CS2= 1.Bmmoles-s’
11-10
1 PRESSURE = 16 mbcir N2O~6.1mmoIess P -1W
0) -
9-8
tot
—
6-5 ‘—“-—S
0
0) — c—I
—~
.4
)D (~~1
~..
0)
)‘I
— (SI
CS
2/02/ CO~ 9-8 FLOW RATES: 0
10-9
Ø.~7
5.1
5.2
5.3
02 = 12.2 mmoles-s’ CS2= 1.8mmoIes.s~ C02= 5.3mmoles.s’ PRESSURE =l4mbcir P~0~ = 0.2 W
11-10
5.4
5.5
5.6
Fig. 1. Typical spectra recordings for CS2/02/N20 and CS2/02/C02 flame laser.
Typical set of spectra recordings is given in fig. 1. Since these spectra are going to be compared, the examples of spectra in fig. 1 are taken with similar flow rates of the additives. This is crucial since the variation of the additive flow rate may induce variations in the output spectrum as well [5]. In order to 436
compare lasing from various vibrational levels of CO, experimental data of laser output spectra, fig. 1, are given in another form, fig. 2. Here, total power output obtained at all transitions within a single vibrational transition is proportional to the length of a single line. Together with the spectral composition of the
Volume 77A, number 6
PHYSICS LETTERS
23 June 1980
On the basis of the comparison of V-V probability curves and spectral composition of the laser power
CO-N,O
output data, fig. 2, one can make following conclusions: (a) N20 has much larger V-V exchange proba-
10’
bifities and therefore it is more efficient additive and (b) CO2 is more spectrally selective additive in comparison with N2 0. First conclusion has been proven already in the early experiments [7,3]. As regards to the second conclusion it is clear from fig. 2 that spectral distribution curves of the laser power output can be related to the shape of V-V probability curves. Therefore, the effect of additives to the power output spectrum can be explained by the influence of the V-V transfer rates for additive CO collisions which vary considerably over the range of CO vibrational levels active in the laser. This changes the inversion ratio of various vibrational levels and hence gain coefficients which are responsible for the laser power output and its spectrum composition.
-
6
—
CO-CO~
5
-
i0
References 0
El]
2
I
-~
W.Q. Jeffers and C.E. Wiswail, J. Quant. Electron. QE-lO (1974) 860.
[2] H.S. Pifioff, S.K. Searles and N. Djeu, App!. Phys. Lett. 19 (1971) 9. and R.A. Carabetta, Appi. Phys. Lett. 22 [3] M.J. Linevsky
I
(1973) 288.
[4] K.D. Foster, G.H. Kimbeil and D.R. Sneiling, J. Quant. ______________________________________________ 1
2
3
4
5
6
7
8
Vibrational
Fig. 2.
Reduced
9
10
11
12
13
14
15
level V
Electron. QE-Il (1975) 253. [5] Z. Babarogié, N. Konjevié and M. Trtica, Rev. Sd Inst., to be published. [6] G. Hancock and LW.M. Smith, AppL Opt. 10 (1971)
V-V exchange probabilities for C0-N
20 and CO-CO2 [6] together with typical spectral composition of the output of CO flame laser. Experimental conditions are same as in fig. 1.
1827. [7] S.K. Searles and N. L~eu,Chem. Phys. Left. 12 (1971) 53~
laser power output in the same figure are given reduced CO-N20 and CO-CO2 V-V exchange probabilities [6].
437