(Submitted November 1, 1984). Kvantovaya Elektron. (Moscow) 12, 1753-1755 (August 1985). An investigation was made of a laser containing a gadolinium ...
scale inhomogeneities of the refractive index which then appeared were characteristic of this type of laser. An increase in the argon content in the active medium could be achieved by increasing the stability of the self-maintained discharge. It would also be desirable to investigate the geometry of the electrodes and of the preionization system with the aim of suppressing small-scale perturbations caused by the inhomogeneity of illumination of the discharge gap, which could be achieved—for example—by using various preionizer configurations proposed in Ref. 9.
Ά . P. Averin, N. G. Basov, E. P. Glotov, V. A. Danilychev, Ν. Ν. Sazhina, A. M. Soroka, and V. I. Yugov, Kvantovaya Elektron. (Moscow) 8, 2063 (1981) [Sov. J. Quantum Electron. 11, 1260 (1981)]. 2 E. P. Glotov, V. A. Danilychev, and N. V. Cheburkin, Tr. Fiz. Inst.
Akad. Nauk SSSR142, 3 (1983). M. C. Richardson, K. Leopold, and A. J. Alcock, IEEE J. Quantum Electron. QE-9, 934 (1973). "V. B. Znamenskil, Yu. A. Rezunkov, A. K. Sinopal'nikov, and V. V. Stepanov, Zh. Tekh. Fiz. 49, 1567 (1979) [Sov. Phys. Tech. Phys. 24, 871 (1979)]. 5 K. R. Manes and H. J. Seguin, J. Appl. Phys. 43, 5073 (1972). 6 D . A. Goryachkin, V. M. Irtuganov, V. P. Kalinin, L. N. Malakhov, and V. P. Yashukov, Zh. Tekh. Fiz. 49, 2656 (1979) [Sov. Phys. Tech. Phys. 24, 1499(1979)]. 7 E. A. Ballik, B. K. Garside, J. Reid, and T. Tricker, J. Appl. Phys. 46, 1322(1975). 8 V. Yu. Baranov, V. M. Borisov, A. A. Vedenov, A. P. Napartovich, and A. P. Strel'tsov, Zh. Tekh. Fiz. 45, 2343 (1975) [Sov. Phys. Tech. Phys. 20,1460(1975)]. 9 M. F. Borisov, V. B. Znamenskil, Yu. A. Rezunkov, et ah, Abstracts of Papers presented at Second AU-Union Conf. on Laser Optics, Leningrad, 1979 [in Russian], p. 58. 3
Translated by A. Tybulewicz
Generation of picosecond pulses by a gadolinium scandium gallium garnet laser R. Danelyus, I. Kuratev, A. Piskarskas, V. Sirutkaftis, E. Shvom, A. Yuozapavichyus, and A. Yankauskas V. Kapsukas Lithuanian State University, Vilnius
(Submitted November 1, 1984) Kvantovaya Elektron. (Moscow) 12, 1753-1755 (August 1985) An investigation was made of a laser containing a gadolinium scandium gallium garnet crystal (GSGG:Cr 3 + :Nd 3 + ) which was operated in the regime of passive mode locking. The duration of the output pulses was ~ 18 psec. The absolute efficiency was approximately 2.5 times higher than that of a YAG:Nd 3 + crystal laser operated under similar conditions. One of the topical tasks in quantum electronics is an increase in the efficiency of flashlamp-pumped solid-state neodymium lasers by a search for active media characterized by strong absorption in the spectral range of the pump radiation. The use of gadolinium scandium gallium garnet crystals activated with chromium and neodymium ions
GSGG
TABLE I. GSGGrCr 3 * :Nd 3 + «*. %
DSF-452
Ep,3
FIG. 1. Investigated system: Λ, is a nontransmitting mirror with a cell through which a dye solution was circulated; GSGG is an active element; Ρ is a plate which sets the polarization; Λ2 is the exit mirror; IMO-2 is an energy meter; AGAT SF-1 is an image-converter camera; FD-24 is a photodiode; AI-256 is an amplitude analyzer; DFS-452 is a spectrograph. 1160
Sov. J. Quantum Electron. 15 (8), Aug. 1985
(GSGG:Cr 3 + :Nd 3 + ) seems to be particularly promising.1 An increase in the laser efficiency is achieved by effective energy transfer from C r 3 + to N d 3 + . A study of the lasing properties of such crystals under free-running and β-switching regimes has demonstrated their advantages over the widely used YAG:Nd 3 + crystals. 23 An increase in the laser efficiency is desirable also in the case of generation of picosecond light pulses. We shall report the results of an experimental investigation of a picosecond laser utilizing a GSGG:Cr 3 + :Nd 3 + crystal with passive mode locking (Fig. 1). A laser resonator of length 1 m was formed by plane mirrors evaporated on
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© 1985 American Institute of Physics
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wedge-shaped substrates. A cell of thickness 0.1 mm was in contact with the nontransmitting mirror and an ethyl solution of dye 3274-u was circulated through this cell. Linear polarization was ensured by a plane-parallel plate of thickness 10 mm, which was located in the resonator and oriented at the Brewster angle. The diameter of the active element was 3 mm and its length was 50 mm; the concentrations of 20 the neodymium and chromium ions were the same (2 Χ10 3 c m ' ) . Mode selection was prevented by leveling one of the ends of the element at an angle of Γ. Pumping was provided by an ISP-2500 lamp, which was placed (together with the active element) inside a monolithic cylindrical reflecting enclosure made of quartz glass. Cooling was by circulation of a 0.2% solution of potassium chromate in distilled water. The duration of the pulses emitted by the flashlamp was ~200 //sec. The operating parameters of the GSGG:Cr 3 + :Nd 3 + laser were determined for different reflection coefficients R2 of the exit mirror. The corresponding threshold pump energies Ep and the energies of a train of ultrashort pulses E, were determined for the investigated mirrors (Table I). The initial transmission of the modulating dye was selected in these experiments so as to ensure a two-threshold passive modelocking regime. A train of ultrashort pulses with 100% modulation and a good reproducibility was then generated (Fig. 2). Such a train usually consisted of 15 pulses. It was found (Table I) that a reduction in the pump energy and an increase in the reflection coefficient resulted in a reduction in the energy of the ultrashort pulse train. For comparison, we also included in Table I the parameters of a YAG:Nd 3 + laser operated under similar conditions. The use of the GSGG:Cr 3 + :Nd 3 + element in the passive mode-locking regime reduced the threshold pump energy by a factor of two compared with the YAG:Nd 3 + crystal. This made it possible to achieve a greater average power. Stable operation of the GSGG laser was observed up to a repetition frequency of 10 Hz. A study of the energy stability of the GSGG:Cr 3 + :Nd 3 + laser was carried out using an exit mirror with the reflection coefficient R2 = 4%. The variation coefficient of the energy of the ultrashort pulse train deduced from the distribution shown in Fig. 3a amounted to 0.04. Therefore, in the case of the GSGG:Cr 3 + :Nd 3 + laser the energy stability of a train of ultrashort pulses was similar to that achieved in a YAG:Nd 3 + laser with passive mode locking.
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Sov. J. Quantum Electron. 15 (8), Aug. 1985
0,4 0,2
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FIG. 3. Histograms of the train energy (a) and the duration (b) of laser pulses.
The lower concentration of defects in GSGG elements used in lasers with passive mode locking, compared with that in YAG lasers, made it possible to achieve single-mode lasing even without an additional stop inside the resonator. The spatial distribution of the radiation was nearly Gaussian and the radius at half intensity was ~ 1 mm. The time parameters of the radiation emitted by the GSGG laser were investigated using an AGAT SF-1 imageconverter camera. A correct estimate of the duration of the ultrashort pulses reaching the camera was obtained by multiplying the pulses in a Fabry-Perot interferometer. An analysis of microphotograms of 100 pulses selected from the maximum of the ultrashort pulse train indicated that under constant conditions the pulse duration varied within the range 12-25 psec (Fig. 3b) and the average value was 18 psec. A study of the pulses selected from different parts of the train showed that at these energies there was no significant change in the duration along the train. The spectral width of the pulses at the lasing wavelength of 1.061 μ was ~ 2 cm ~' and it increased somewhat at the end of the train. Therefore, the use of GSGG:Cr 3 + :Nd 3 + elements made it possible to reduce the duration of the output picosecond pulses by a factor of 1.5-2 compared with YAG:Nd 3 + and to increase by a factor of 2.5 the absolute efficiency of the laser. Έ . V. Zharkiov, Ν. Ν. Il'ichev, V. V. Laptev, A. A. Malyutin, V. G. Ostroumov, P. P. Pashinin, A. S. Pimenov. V. A. Smirnov, and I. A. Scherbakov, Kvantovaya Elektron. (Moscow) 10, 140 (1983) [Sov. J. Quantum Electron. 13, 82 (1983)]. 2 E. V. Zharkiov, V. A. Zhitnyuk, G. M. Zverev, S. P. Kalitin, 1.1. Kuratev, V. V. Laptev, A. M. Onishchenko, V. V. Osiko, V. A. Pashkov, A. S. Pimenov, A. M. Prokhorov, V. A. Smirnov, M. F. Stel'makh, A. V. Shestakov, and I. A. Scherbakov, Kvantovaya Elektron. (Moscow) 9, 2531 (1982) [Sov. J. Quantum Electron. 12, 1652 (1982)]. 3 E. V. Zhrikov, M. B. Zhitkova, G. M. Zverev, M. P. Isaev, S. P. Kalitin, I. I. Kuratev, V. R. Kushnir, V. V. Laptev, V. V. Osiko, V. A. Pashkov, A. S. Pimenov, A. M. Prokhorov, V. A. Smirnov, M. F. Stel'makh, A. V. Shestakov, and I. S. Shcherbakov, Kvantovaya Elektron. (Moscow) 10, 1961 (1983) [Sov. J. Quantum Electron. 13, 1306 (1983)]. Translated by A. Tybulewicz
Danelyuse/a/.
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