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Efficient up-conversion in CdSe
Volume
17, number
OPTICS COMMUNICATIONS
2
EFFICIENT UP-CONVERSION
A. FERRARIO
May 1976
IN Cd Se *
and M. GARB1
USE, P.O. Box 3986, 20100 Milano, Italy Received
15 January
1976
In this work up-conversion in CdSe with a HF laser as a pump and an experimental quantum 40% is reported. With this device, it is possible to obtain up-conversion in the 8-25 fi wavelength
An up-conversion in CdSe with an electric discharge HF laser as a pump and a quantum efficiency higher than 40% is reported. Many papers reported several theoretical and experimental investigations on the efficiency of infrared wavelength up-conversion. A total conversion efficiency was obtained with a SOmm long LiNbO, crystal, and a ruby laser as a pump [ 11. Up-conversion devices utilizing ADP, LiNbO, and Ag,AsS, were made for the enhancement in the threshold sensitivity of infrared radiation detectors [2], for optical light gates with picosecond resolution [3], and for image converters [4]. Bloom [5] reported efficient infrared up-conversion in metal vapours. The CdSe crystal has a high non-linear coefficient (d = 4,s X 10e8 e.s.u.) with a figure of merit six times larger than that of the LiNb03 crystal and a 0.75 to 25 /J transparency range. It is “phase matchable” in a large range of wavelengths, and the pump wavelength giving the widest tuning range is close to the most intense HF laser lines. Moreover, commercial crystals 4 or 5 cm in length and with very good optical quality are today available. (The measured absorption coefficient at 3.39 /.J of the CdSe crystal supplied by Gould Inc. is 0.01 cm-l). Our up-conversion setup is shown in fig. 1. The HF laser was constructed in a transverse excitation configuration. The oscillator emission was restricted to a TEMOO mode and a single line with a diffraction grating. The output pulses were obtained with 4 kW peak power, 250 nsec duration and 5 p.p.s. * Work supported 158
by Contract
CNR-CISE
no 73.01435
efficiency range.
higher
than
Ll
Detector
Fig, 1. Diagram
of up-conversion
experiment.
repetition rate. The CO2 laser is cw, with oscillation in the TEMOO mode and in one single line. Two ZnSe lenses with different focal length are used to obtain the same beam waist size and position in the crystal. A set fused silica, Brewster angle windows behind the crystal is a very simple and efficient filter for the CO2 and HF lasers (the borosilicate glass could also be used as an efficient filter). The 3-cm long CdSe crystal is oriented with the geometrical axis at 80” to the optical axis and for type II phase-matching. The angular tuning curve for up-conversion is shown in fig. 2. In our experimental condition the crystal aperture length 1, is 4 cm, the double refraction parameter B [6] is 0.82 and the focusing parameter ,$ is 0.4. With this geometrical condition the effective crystal length is I* = &i& where 1 is the crystal length, b the confocal parameter in the crystal and h a dimensionless quantity derived from the Boyd and Kleinmann theory [6]. In our condition I* = 2.738 cm. The exact expression for the up-converted electric
OPTICS COMMUNICATIONS
Volume 17, number 2
May 1976
matching curve of fig. 2, and the measurement of the sinc2 (4 AKl) curve shows an external angle with 2” + 0.5” full base width to be compared with a theoretical value of 2.5”. The spectral bandwidth for the crystal in our experimental condition is 10 cm-l. This bandwidth was checked by changing the wavelengths of the CO2 laser.
Fig. 2. Angular tuning for CdSe up-conversion, with 2.72 IJ wavelength as laser pump.
field strength with ideal phase matching is given by
In conclusion, we have demonstrated a very efficient up-conversion process in CdSe crystal. Moreover, using a HF laser as a pump with several strong lines in the 2.7-3 P range, it is possible to obtain the phase-matching for the up-conversion in a very wide range of wavelengths (8 to 25 P of the infrared signal). Other experiments are in progress to achieve the total up-conversion, using a AgGaSe, crystal which is phase-matchable in the IO- 17 P range with a Nd-YAG laser as a pump. The merit figure of AgGaSe, is three times higher than that of prousite and two times higher than that of CdSe crystal.
[71: El sin (I*//,_),
E3 = (~:kl/ti:k3)~‘~
where 4nde
1, = -
C2
(w2 w2/k 13
k
13
The authors acknowledge the useful discussions with dr. M. Musci and Mr. R. Canevari for the construction of the CO, laser.
)1’2E 2.
w3, w1 are the angular frequencies of the up-converted radiation of the pump laser and the infrared radiation, respectively, K, and KS are the wave vectors, de is the effective non-linear coefficient, c the light velocity, E2 and El are the electric field strengths of the laser pump (HF laser) and the infrared radiation (CO2 laser). The quantum conversion efficiency is: r14 = sin2([*/I,). For a laser pump intensity of 6 MW/cm2, the theoretical quantum conversion is 75.5%, the measured efficiency conversion is higher than 40% and the power gain is 2. The experimental phase-matching angle en, = 70.5” + 0.5” is in good agreement with the phase-
References [l] T.R. Gurski, Appi. Phys. Lett. 23 (1973) 273. (21 E.S. Voronin, I.N. Matveev, S.M. Pshenichnikov, S.V. Solomatin and V.V. Shuvalov, Sov. J. Quant. Electron. 5 (1975) 126. (31 H. Mahr and M.D. Hirsch, Optics. Commun. 13 (1975) 96. [4] G.P. Arumov, E.S. Voronin, Yu A. Il’inskii, V.E. Prokopenko and VS. Solomatin, Sov. J. Quant. Electron, 4 (1975) 1163. [5] D.M. Bloom, JamesT. Yardley, J.F. Young and S.E. Harris, Appl. Phys. Lett. 24 (1974) 427. (61 G.D. Boyd and D.A. Kleinman, J. Appl. Phys. 39 (1968) 3597. [7] J.A. Armstrong, M. Bloembergen, I. Ducuing and P.S. Pershan, Phys. Rev. 127 (1962) 1918.
159
17, number
OPTICS COMMUNICATIONS
2
EFFICIENT UP-CONVERSION
A. FERRARIO
May 1976
IN Cd Se *
and M. GARB1
USE, P.O. Box 3986, 20100 Milano, Italy Received
15 January
1976
In this work up-conversion in CdSe with a HF laser as a pump and an experimental quantum 40% is reported. With this device, it is possible to obtain up-conversion in the 8-25 fi wavelength
An up-conversion in CdSe with an electric discharge HF laser as a pump and a quantum efficiency higher than 40% is reported. Many papers reported several theoretical and experimental investigations on the efficiency of infrared wavelength up-conversion. A total conversion efficiency was obtained with a SOmm long LiNbO, crystal, and a ruby laser as a pump [ 11. Up-conversion devices utilizing ADP, LiNbO, and Ag,AsS, were made for the enhancement in the threshold sensitivity of infrared radiation detectors [2], for optical light gates with picosecond resolution [3], and for image converters [4]. Bloom [5] reported efficient infrared up-conversion in metal vapours. The CdSe crystal has a high non-linear coefficient (d = 4,s X 10e8 e.s.u.) with a figure of merit six times larger than that of the LiNb03 crystal and a 0.75 to 25 /J transparency range. It is “phase matchable” in a large range of wavelengths, and the pump wavelength giving the widest tuning range is close to the most intense HF laser lines. Moreover, commercial crystals 4 or 5 cm in length and with very good optical quality are today available. (The measured absorption coefficient at 3.39 /.J of the CdSe crystal supplied by Gould Inc. is 0.01 cm-l). Our up-conversion setup is shown in fig. 1. The HF laser was constructed in a transverse excitation configuration. The oscillator emission was restricted to a TEMOO mode and a single line with a diffraction grating. The output pulses were obtained with 4 kW peak power, 250 nsec duration and 5 p.p.s. * Work supported 158
by Contract
CNR-CISE
no 73.01435
efficiency range.
higher
than
Ll
Detector
Fig, 1. Diagram
of up-conversion
experiment.
repetition rate. The CO2 laser is cw, with oscillation in the TEMOO mode and in one single line. Two ZnSe lenses with different focal length are used to obtain the same beam waist size and position in the crystal. A set fused silica, Brewster angle windows behind the crystal is a very simple and efficient filter for the CO2 and HF lasers (the borosilicate glass could also be used as an efficient filter). The 3-cm long CdSe crystal is oriented with the geometrical axis at 80” to the optical axis and for type II phase-matching. The angular tuning curve for up-conversion is shown in fig. 2. In our experimental condition the crystal aperture length 1, is 4 cm, the double refraction parameter B [6] is 0.82 and the focusing parameter ,$ is 0.4. With this geometrical condition the effective crystal length is I* = &i& where 1 is the crystal length, b the confocal parameter in the crystal and h a dimensionless quantity derived from the Boyd and Kleinmann theory [6]. In our condition I* = 2.738 cm. The exact expression for the up-converted electric
OPTICS COMMUNICATIONS
Volume 17, number 2
May 1976
matching curve of fig. 2, and the measurement of the sinc2 (4 AKl) curve shows an external angle with 2” + 0.5” full base width to be compared with a theoretical value of 2.5”. The spectral bandwidth for the crystal in our experimental condition is 10 cm-l. This bandwidth was checked by changing the wavelengths of the CO2 laser.
Fig. 2. Angular tuning for CdSe up-conversion, with 2.72 IJ wavelength as laser pump.
field strength with ideal phase matching is given by
In conclusion, we have demonstrated a very efficient up-conversion process in CdSe crystal. Moreover, using a HF laser as a pump with several strong lines in the 2.7-3 P range, it is possible to obtain the phase-matching for the up-conversion in a very wide range of wavelengths (8 to 25 P of the infrared signal). Other experiments are in progress to achieve the total up-conversion, using a AgGaSe, crystal which is phase-matchable in the IO- 17 P range with a Nd-YAG laser as a pump. The merit figure of AgGaSe, is three times higher than that of prousite and two times higher than that of CdSe crystal.
[71: El sin (I*//,_),
E3 = (~:kl/ti:k3)~‘~
where 4nde
1, = -
C2
(w2 w2/k 13
k
13
The authors acknowledge the useful discussions with dr. M. Musci and Mr. R. Canevari for the construction of the CO, laser.
)1’2E 2.
w3, w1 are the angular frequencies of the up-converted radiation of the pump laser and the infrared radiation, respectively, K, and KS are the wave vectors, de is the effective non-linear coefficient, c the light velocity, E2 and El are the electric field strengths of the laser pump (HF laser) and the infrared radiation (CO2 laser). The quantum conversion efficiency is: r14 = sin2([*/I,). For a laser pump intensity of 6 MW/cm2, the theoretical quantum conversion is 75.5%, the measured efficiency conversion is higher than 40% and the power gain is 2. The experimental phase-matching angle en, = 70.5” + 0.5” is in good agreement with the phase-
References [l] T.R. Gurski, Appi. Phys. Lett. 23 (1973) 273. (21 E.S. Voronin, I.N. Matveev, S.M. Pshenichnikov, S.V. Solomatin and V.V. Shuvalov, Sov. J. Quant. Electron. 5 (1975) 126. (31 H. Mahr and M.D. Hirsch, Optics. Commun. 13 (1975) 96. [4] G.P. Arumov, E.S. Voronin, Yu A. Il’inskii, V.E. Prokopenko and VS. Solomatin, Sov. J. Quant. Electron, 4 (1975) 1163. [5] D.M. Bloom, JamesT. Yardley, J.F. Young and S.E. Harris, Appl. Phys. Lett. 24 (1974) 427. (61 G.D. Boyd and D.A. Kleinman, J. Appl. Phys. 39 (1968) 3597. [7] J.A. Armstrong, M. Bloembergen, I. Ducuing and P.S. Pershan, Phys. Rev. 127 (1962) 1918.
159