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Second harmonic generation in proustite using a HF laser as the fundamental
Volume 15, number 1
OPTICS COMMUNICATIONS
September 1975
SECOND HARMONIC GENERATION IN PROUSTITE USING A HF LASER AS THE FUNDAMENTAL D.P. JUYAL* and G.C. THOMAS Department of Electronics, The University, Southampton S095NH, UK Received 21 May 1975 Second harmonic generation in proustite is reported for the first time using a HF laser as the fundamental. The angular dependence of the S.H. power has been studied. A conversion efficiency of about 3% has been obtained. The proustite crystal (Ag3AsS3) , first synthesized by Royal Radar Establishment [ 1 - 3 ] , is birefringent and acentric, and has a good transmission band from 0.6 to beyond 13/am which makes it a potential nonlinear optical material for the development of tunable infrared sources [4,5] and also for the image-upconversion o f the 10.6/am radiation from the CO 2 laser into the visible (6). The crystal belongs to the point group 3m and is negative uniaxial with a birefringence of n o - n e = 0.2. The Sellmeier equations of the form 9.4454 n 2 = 9.220 +~2 _ 0.1264
1733 1 0 0 0 - ~2
and n 2 = 7.007 +
0.3230 X2-0.1192
660 1 0 0 0 - X2
can be used to calculate the ordinary and extraordinary indices between 0.6 and 20/am at 20°C (X in /am). From Miller's rule, we expect that the high refractive index of proustite would indicate a large nonlinearity. Measurements of the nonlinear coefficients have confirmed this, as the values are: d22 = 50d36(KDP ) and d31 = 30d36(KDP). The coefficient d33 was not measured and the Kleinman condition was assumed (d15 = d31 ). In view o f the suitability of proustite as a frequency doubler we studied for the first time S.H.G. in this crystal using HF laser [7] wavelengths as fundamentals. The HF laser was designed and developed at our * Present address: Instruments Research and Development Establishment, Dehra Dun, India.
26
laboratory and operated on eight rotational lines selectively in the TEM00 mode. A simple computer program (table 1) was run to evaluate the phase-matching angles o f HF laser wavelengths for two types of proustite crystal. However, the S.H.G. was tried only in one type. The experimental setup is shown in fig. 1. The crystal used was a BDH sample (SP 4) of 1 cm length, refractive index (r.i.) = 2.7 and cut at 25 ° from the face normal. The phase-matching angle (X = 2.705/am) of the crystal is 22.76 ° , therefore the normal is to be rotated by an angle 25 ° - 22.76 ° = 2.24 ° internally in order to match the indices of the fundamental and the second harmonic signals. The external phasematching angle will be 2.24 ° X r.i. ~ 6 °. The following expression was used to evaluate the S.H. power (erg/sec) in proustite using the appropriate values of the different parameters. W(2w) - 512n5d2L 2 W(w)
n( 2w )n 2 (co) ~,2cA ' where d = nonlinear coefficient (C.G.S.) = 7 × 10 -8 e.s.u., L = length of the crystal = 1 cm, W(co) = pump power = 500 watt, n(2co) = second harmonic r.i., n(co) = fundamental r.i., ~, = pump wavelength = 2.705/am, c = velocity of light, A = spot area of the pump laser beam on the crystal focussed by KBr lens = 3 X 10 - 3 cm 2. We observed S.H. for all the rotational lines o f the H.F. laser having peak power of 1 kW for single wavelength and TEM00 mode. Fig. 2 shows the fundamental (2.705/am) and the S.H. signal (1.35/am). Incidently the S.H. frequency coincides with the iodine laser wavelength. A conversion efficiency of about 3% has been obtained which agrees well with the calculated
September 1975
OPTICAL COMMUNICATIONS
Volume 15, number 1 Table 1 Phase-matching angles in proustite for S.H.G. Wavelength 6um)
2.5000 2.6000 2.7000 2.8000 2.9000 3.0000 2.6726 2.7074 2.7440 2.7604 2.7825 2.7952 2.8350 2.8705
HF
r.i. (ordinary) fundamental
2.7475 2.7463 2.7453 2.7443 2.7434 2.7425 2.7455 2.7452 2.7448 2.7447 2.7444 2.7443 2.7439 2.7436
r i. (ordinary) S.H.
r.i. Int. (extraordinary) angle S.H.
External angle 25 ° crystal
(b) 26.5 ° crystal
2.7919 2.7873 2.7832 2.7797 2.7765 2.7736 2.7843 2.7830 2.7816 2.7810 2.7803 2.7798 2.7785 2.7774
2.5632 2.5596 2.5564 2.5537 2.5512 2.5487 2.5573 2.5562 2.5552 2.5547 2.5541 2.5538 2.5528 2.5519
- 0.84 - 3.55 - 6.00 - 8.23 -10.27 -12.14 -- 5.35 - 6.17 - 7.01 - 7.37 - 7.86 - 8.13 - 8.86 - 9.69
- 4.96 - 7.68 -10.15 -12.41 -14.47 -16.37 - 9.50 -10.33 -11.17 -11.54 -12.03 -12.31 -13.02 -13.88
24.70 23.71 22.82 22.01 21.27 20.60 23.05 22.76 22.45 22.32 22.14 22.04 21.80 21.48
(a)
HF LASER BEAM
0 DEIECTOR
50CM FOCAL LENGTH K Br LENS
PROUSTITE CRYSTAL LENS.
Fig. 1. Experimental set up for S.H.G. in proustite using a HF laser.
Fig. 2a. HF fundamental (2.705 pm). Horiz. scale: 100 ns/div; vert. scale: 200 mV/div.
Fig. 2b. S.H. signal (1.35 pm) in proustite. Horiz. scale: 100 ns/div; vert. scale: 5 mV/div.
27
Volume 15, number 1
gu
p~n
OPTICAL COMMUNICATIONS
We wish to thank Dr. R.C. Smith, Dr. D.C. Hanna, Dr. Bary-Luther Davies and Mr. A.J. Turner for fruitful discussions. One of us (D.P.J.) is grateful to the Jawahar lal Nehru Memorial Trust (U.K.) for awarding a scholarship. This work is supported by a grant from the Science Research Council.
20-
;I
W | ,o =C U~
References
,/
t ~Am~L~S
| iN OEGRtlI~.
Fig. 3. Angular dependence of S.H. power in proustite using the 2.71 pm line from the HF laser as fundamental.
value. Fig. 3 shows the angular dependence of S.H. power for the 2.705/am fundamental. The BDH sample was not of satisfactory quality, but it is expected that the conversion efficiency would further improve if a crystal of better quality is employed and the pump beam on the crystal is properly tightened.
28
September 1975
[1] W. Bardsley, P.H. Davies, M.V. Hobden, K.F. Hulme, O. Jones, W. Pomeroy and J. Warner, Opto-electronics 1 (1969) 29. [2] M.V. Hobden, Opto-electronics 1 (1969) 159. [3] K.F. Hulme, O. Jones, P.H. Davies and M.V. Hobden, Appl. Phys. Letters 10 (1967) 133. [4] D.C. Hanna, R.C. Smith and C.R. Stanley, Opt. Commun. 4 (1971) 300. [5] D. Cotter, D.C. Hanna, B. Luther-Davies, R.C. Smith and A.J. Turner, Opt. Commun. 11 (1974) 54. [6] E.S. Veronin, V.S. Solomation and V. Shuvalov, Optoelectronics 6 (1974) 189. [7] D.P. Juyal, 'Design and Operation of Transversely excited pulsed HF laser', Techn. Rep. (Nov. 1974), Dep. of Electronics, The University, South., U.K.
OPTICS COMMUNICATIONS
September 1975
SECOND HARMONIC GENERATION IN PROUSTITE USING A HF LASER AS THE FUNDAMENTAL D.P. JUYAL* and G.C. THOMAS Department of Electronics, The University, Southampton S095NH, UK Received 21 May 1975 Second harmonic generation in proustite is reported for the first time using a HF laser as the fundamental. The angular dependence of the S.H. power has been studied. A conversion efficiency of about 3% has been obtained. The proustite crystal (Ag3AsS3) , first synthesized by Royal Radar Establishment [ 1 - 3 ] , is birefringent and acentric, and has a good transmission band from 0.6 to beyond 13/am which makes it a potential nonlinear optical material for the development of tunable infrared sources [4,5] and also for the image-upconversion o f the 10.6/am radiation from the CO 2 laser into the visible (6). The crystal belongs to the point group 3m and is negative uniaxial with a birefringence of n o - n e = 0.2. The Sellmeier equations of the form 9.4454 n 2 = 9.220 +~2 _ 0.1264
1733 1 0 0 0 - ~2
and n 2 = 7.007 +
0.3230 X2-0.1192
660 1 0 0 0 - X2
can be used to calculate the ordinary and extraordinary indices between 0.6 and 20/am at 20°C (X in /am). From Miller's rule, we expect that the high refractive index of proustite would indicate a large nonlinearity. Measurements of the nonlinear coefficients have confirmed this, as the values are: d22 = 50d36(KDP ) and d31 = 30d36(KDP). The coefficient d33 was not measured and the Kleinman condition was assumed (d15 = d31 ). In view o f the suitability of proustite as a frequency doubler we studied for the first time S.H.G. in this crystal using HF laser [7] wavelengths as fundamentals. The HF laser was designed and developed at our * Present address: Instruments Research and Development Establishment, Dehra Dun, India.
26
laboratory and operated on eight rotational lines selectively in the TEM00 mode. A simple computer program (table 1) was run to evaluate the phase-matching angles o f HF laser wavelengths for two types of proustite crystal. However, the S.H.G. was tried only in one type. The experimental setup is shown in fig. 1. The crystal used was a BDH sample (SP 4) of 1 cm length, refractive index (r.i.) = 2.7 and cut at 25 ° from the face normal. The phase-matching angle (X = 2.705/am) of the crystal is 22.76 ° , therefore the normal is to be rotated by an angle 25 ° - 22.76 ° = 2.24 ° internally in order to match the indices of the fundamental and the second harmonic signals. The external phasematching angle will be 2.24 ° X r.i. ~ 6 °. The following expression was used to evaluate the S.H. power (erg/sec) in proustite using the appropriate values of the different parameters. W(2w) - 512n5d2L 2 W(w)
n( 2w )n 2 (co) ~,2cA ' where d = nonlinear coefficient (C.G.S.) = 7 × 10 -8 e.s.u., L = length of the crystal = 1 cm, W(co) = pump power = 500 watt, n(2co) = second harmonic r.i., n(co) = fundamental r.i., ~, = pump wavelength = 2.705/am, c = velocity of light, A = spot area of the pump laser beam on the crystal focussed by KBr lens = 3 X 10 - 3 cm 2. We observed S.H. for all the rotational lines o f the H.F. laser having peak power of 1 kW for single wavelength and TEM00 mode. Fig. 2 shows the fundamental (2.705/am) and the S.H. signal (1.35/am). Incidently the S.H. frequency coincides with the iodine laser wavelength. A conversion efficiency of about 3% has been obtained which agrees well with the calculated
September 1975
OPTICAL COMMUNICATIONS
Volume 15, number 1 Table 1 Phase-matching angles in proustite for S.H.G. Wavelength 6um)
2.5000 2.6000 2.7000 2.8000 2.9000 3.0000 2.6726 2.7074 2.7440 2.7604 2.7825 2.7952 2.8350 2.8705
HF
r.i. (ordinary) fundamental
2.7475 2.7463 2.7453 2.7443 2.7434 2.7425 2.7455 2.7452 2.7448 2.7447 2.7444 2.7443 2.7439 2.7436
r i. (ordinary) S.H.
r.i. Int. (extraordinary) angle S.H.
External angle 25 ° crystal
(b) 26.5 ° crystal
2.7919 2.7873 2.7832 2.7797 2.7765 2.7736 2.7843 2.7830 2.7816 2.7810 2.7803 2.7798 2.7785 2.7774
2.5632 2.5596 2.5564 2.5537 2.5512 2.5487 2.5573 2.5562 2.5552 2.5547 2.5541 2.5538 2.5528 2.5519
- 0.84 - 3.55 - 6.00 - 8.23 -10.27 -12.14 -- 5.35 - 6.17 - 7.01 - 7.37 - 7.86 - 8.13 - 8.86 - 9.69
- 4.96 - 7.68 -10.15 -12.41 -14.47 -16.37 - 9.50 -10.33 -11.17 -11.54 -12.03 -12.31 -13.02 -13.88
24.70 23.71 22.82 22.01 21.27 20.60 23.05 22.76 22.45 22.32 22.14 22.04 21.80 21.48
(a)
HF LASER BEAM
0 DEIECTOR
50CM FOCAL LENGTH K Br LENS
PROUSTITE CRYSTAL LENS.
Fig. 1. Experimental set up for S.H.G. in proustite using a HF laser.
Fig. 2a. HF fundamental (2.705 pm). Horiz. scale: 100 ns/div; vert. scale: 200 mV/div.
Fig. 2b. S.H. signal (1.35 pm) in proustite. Horiz. scale: 100 ns/div; vert. scale: 5 mV/div.
27
Volume 15, number 1
gu
p~n
OPTICAL COMMUNICATIONS
We wish to thank Dr. R.C. Smith, Dr. D.C. Hanna, Dr. Bary-Luther Davies and Mr. A.J. Turner for fruitful discussions. One of us (D.P.J.) is grateful to the Jawahar lal Nehru Memorial Trust (U.K.) for awarding a scholarship. This work is supported by a grant from the Science Research Council.
20-
;I
W | ,o =C U~
References
,/
t ~Am~L~S
| iN OEGRtlI~.
Fig. 3. Angular dependence of S.H. power in proustite using the 2.71 pm line from the HF laser as fundamental.
value. Fig. 3 shows the angular dependence of S.H. power for the 2.705/am fundamental. The BDH sample was not of satisfactory quality, but it is expected that the conversion efficiency would further improve if a crystal of better quality is employed and the pump beam on the crystal is properly tightened.
28
September 1975
[1] W. Bardsley, P.H. Davies, M.V. Hobden, K.F. Hulme, O. Jones, W. Pomeroy and J. Warner, Opto-electronics 1 (1969) 29. [2] M.V. Hobden, Opto-electronics 1 (1969) 159. [3] K.F. Hulme, O. Jones, P.H. Davies and M.V. Hobden, Appl. Phys. Letters 10 (1967) 133. [4] D.C. Hanna, R.C. Smith and C.R. Stanley, Opt. Commun. 4 (1971) 300. [5] D. Cotter, D.C. Hanna, B. Luther-Davies, R.C. Smith and A.J. Turner, Opt. Commun. 11 (1974) 54. [6] E.S. Veronin, V.S. Solomation and V. Shuvalov, Optoelectronics 6 (1974) 189. [7] D.P. Juyal, 'Design and Operation of Transversely excited pulsed HF laser', Techn. Rep. (Nov. 1974), Dep. of Electronics, The University, South., U.K.