PHYSICS

A. A. KAMINSKII, L. S. KORNIENKO,
Corresponding Member of the USSR Academy of Sciences A. M. PROKHOROV

CONTINUOUS SOLAR OPTICAL QUANTUM GENERATOR ON Dy\(^{2+}\) IN CaF\(_2\)

The first optical quantum generator (OQG) using solar radiation for excitation was realized on Dy\(^{2+}\) in CaF\(_2\) at the temperature of liquid neon (27°K). To focus the radiation of the sun

Fig. 1. Photograph of the experimental setup

a spherical mirror of diameter \(\sim 350\) mm was used, at whose focus there was placed a Dewar vessel with the working crystal of dimensions \(25.4 \times 6.35 \times 3.18\) mm \((^1)\).

In the present communication a solar OQG on Dy\(^{2+}\) in CaF\(_2\), operating at the temperature of liquid nitrogen (77°K), is described. The crystals used were grown from the melt in a fluorinating atmosphere by the crucible-lowering method, with an initial DyF\(_3\) concentration of about 0.03%. To convert Dy\(^{3+}\) into Dy\(^{2+}\), \(\gamma\)-radiation from a cobalt source (Co\(^{60}\)) was used. The irradiation dose was \(\sim 10^6\) r. The experiments were carried out in Moscow, in the twenties of August 1964, at noon, under a cloudless sky.

Excitation of the generator was carried out in the absorption band of the \(4f \to 5d\) transitions, lying from 25,000 to 10,000 cm\(^{-1}\). The generation corresponds to the transition \({}^{5}I_7 \to {}^{5}I_8\), terminating approximately 35 cm\(^{-1}\) above the ground state (2). Solar radiation was collected by a standard glass aluminized mirror from a KPT-15 motion-picture projection unit with a diameter of \(\sim 450\) mm. The quality of the mirror used was not high, which produced, at the focus, an image of the sun with a diameter of \(\sim 10\) mm.

Fig. 2. Time dependence of generation. The value of one scale division is 250 μsec

The design of the generator made it possible to orient the mirror to any point in the sky (see Fig. 1).

For more effective transfer of the sun’s radiation into the crystal, a conical condenser made of optically homogeneous K8 glass or fluorite was used; the working sample, with dimensions \(26 \times 3 \times 4\) mm, was attached to it by means of optical contact. The optical resonator was provided by silver mirrors deposited on the end faces of the crystal, whose parallelism was no worse than \(15''\). The transmission of one mirror was \(\sim 3\%\). The condenser with the crystal was located in a cryostat with pure liquid nitrogen. The mirror had an effective area of \(\sim 1500\) cm\(^2\), which ensured an operating regime of the generator close to threshold. Slight partial shading of the mirror led to disruption of generation. Preliminary laboratory investigations of the generator with excitation from a xenon lamp of the DKSP type showed that the generation wavelength was \(2.3590 \pm 10\) Å. Figure 2 shows an oscillogram of the time dependence of generation. An InSb photoresistor with a germanium filter was used as the radiation indicator. The time constant of the recording circuit was about \(\sim 10^{-6}\) sec. The power of the solar optical quantum generator was estimated to be several microwatts.

The authors are grateful to V. V. Osiko for providing the crystals, to V. N. Lukanin for fabricating the condenser and processing the crystals, and to D. M. Litvak, L. D. Kolpakov, A. Ya. Stepanov, and V. A. Skirdonov, who took part in preparing the experiment.

Institute of Nuclear Physics
Moscow State University
named after M. V. Lomonosov

P. N. Lebedev Physical Institute
Academy of Sciences of the USSR

Received
4 IX 1964

REFERENCES

1. Z. J. Kiss, H. R. Lewis, R. C. Duncan Jr., Appl. Phys. Let., 2, No. 5, 93 (1963).
2. A. Yariv, J. P. Gordon, Proc. IEEE, 51, No. 1, 30 (1964).