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Stimulated emission from Er3+ ions in yttrium aluminum garnet crystals at λ = 2.94 μ

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1975 Sov. J. Quantum Electron. 4 1039

(http://iopscience.iop.org/0049-1748/4/8/L28)

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Stimulated emission from Er3 ions in yttrium aluminum garnetcrystals at λ = 2.94 μ

E. V. Zharikov, V. I. Zhekov, L. A. Kulevskii, T. M. Murina, V. V. Osiko, A. M. Prokhorov, A. D.Savel'ev, V. V. Smirnov, B. P. Starikov, and M. I. Timoshechkin

P. N. Lebedev Physics Institute, USSR Academy of Sciences

(Submitted March 25,1974)Kvant. Elektron. 1, 1867-1869 (August 1974)

Stimulated emission due to the 4/n/2-4/i3/2 transition (X = 2.936 ju,) in yttriumaluminum garnet (Y3A15O12) doped with Er3+ ions (30 wt%) was observed for thefirst time at 300 °K. The output energy from crystals of 50x3 mm dimensions was0.3 J under free-oscillation conditions and 0.05 J in the case of Q switching. Thelifetime of the 4 /n / 2 level was determined for crystals with 3-30 wt% Er3+. Theenergy from the higher Er3+ levels relaxed in a cascade manner through 4 / n / 2 to4f1 13/2-

In some physical investigations and practical applicationsit would be desirable to have laser materials doped withrare earth ions because this would extend the availableemission frequencies in the infrared range. Stimulatedemission from the Dy3+ and Er3+ ions at wavelengths X =3.022 and 2.69 fJ., respectively, was reported in refs. 1-3.

The present paper reports a study of an investigationof the energy and spectral characteristics of the emissionfrom Er3+ ions in yttrium aluminum garnet crystals. Weinvestigated a series of mixed crystals of the x(Er3Al5O12) '(100-x) (Y3A15O12) system, where x = 3, 5, 10, 20, or 30wt.%. These crystals were grown by the Czochralskimethod in a controlled atmosphere using a method de-scribed in ref. 4.

Active elements were cylindrical rods 5 mm diame-ter and 40 mm long. The ends of the rods were polishedto a planeness of X/10 and the angle between the ends was10-15 ang. min. The laser action occurred in crystalswith x = 10, 20, and 30 wt.%. The lowest threshold and thehighest energy yield were obtained for x = 30%.

Under free-oscillation conditions (T = 300°K) thethreshold was 190 J for crystals of 3 mm diameter and 60mm long. These crystals were doped with x = 30 wt.%Er3+ and their optical axes were oriented along the [100]direction. We determined the output energy under free-oscillation and Q- switching conditions. When the pumpingenergy exceeded the threshold value by a factor of 2.5, theoutput energy was 0.3 J under free-oscillation conditionsand 0.005 J in the Q-switching case.

The transition responsible for the stimulated emis-sion was identified by investigating the free-oscillationspectrum. The output frequency was converted by mixingthe radiation of the investigated and ruby lasers in a crys-tal of LiIO3 and recording the resultant sum frequency inthe visible range using a PGS-2 spectrograph.

The advantage of this method of recording infraredspectra was the ability to cover a wide spectral range andyet detect the fine structure. Moreover, this method al-lowed us to use the fast-response streak camera in orderto study the kinetics of the infrared emission. The e— oocollinear interaction was used in the frequency conversionprocess. The phase-matching conditions were achievedby rotating the nonlinear crystal. The width of the ruby

laser spectrum did not exceed 0.03 cm and its emissionwavelength was 694.55 ± 0.05 nm.

The measured emission wavelength of the garnetlaser, reduced to vacuum, was 2936.4 ± 2 nm.

The energy spectrum of the emission from Er3 inyttrium aluminum garnet was also studied in refs. 5 and 6.According to their results, the stimulated emission shouldbe attributed to the 4In/2~4Ii3/2 transition (Fig. 1).

The lifetime of the 4In/2 level at 300°K was deter-mined for crystals with x = 5, 10, 20, or 30 wt.%. Thesecrystals were pumped with pulses of 80 fisec duration anda PbS photoresistor with a time constant of ~50 Msec wasused as the detector. The luminescence line was selectedwith an IKS-12 monochromator. The lifetime was thesame in all these crystals and it was equal to 320 Msec.The luminescence buildup time in the 3 M region (4In/2~

fl/Z

5/2

ty'it/12

.Will-W370 ,'10360 /„/„-W28I l2

70252

Fig. 1. Energy scheme of the levels of Er3+ in yttrium aluminum garnetcrystals, taken from refs. 5 and 6.

1039 gov. J. Quant. Electron., Vol. 4. No. 8. February 1975 Copyright © 1975 American Institute of Physics 1039

*I13/2) was less than 80 usec and in the 1.6 n region(4Il3/2~4Ii5/2) it was 300 Msec. The luminescence in thefirst region was extremely weak compared with the lumi-nescence in the second region and this was true of crystalswith different concentrations of erbium.

In agreement with refs. 7 and 8, the luminescence dueto the transition from the "83/2 to the 4I13/2 level was strong-ly quenched (the quantum efficiency was less than 10%),whereas the luminescence from the levels 4F9/2 and 4I9/2was not observed at all. Consequently, we concluded thatthe excitation from the high-energy levels of Er3+ relaxedin a cascade manner through 4In/2 to 4Ii3/2 (Fig. 1) andnonradiative transitions suppressed the In/2~4Ii3/2 rad-iative channel. The lower laser level of the 4In/2~4Ii3/2transition was separated from the ground state 4Ii5/2 bymore than 6000 cm"1. It decayed slowly even at high con-centrations of Er3+ (the lifetime at 300°K in crystals with1% and 30% Er3+ was 6 and 1 msec, respectively). Con-sequently, the system was of the four-level type at thebeginning of the laser action but the stimulated transferof the particles to the 4Ii3/2 level resulted in its rapidfilling, elimination of the population inversion, and break-down of the laser action. Stimulated emission spikes wereobserved only at the top of the pumping pulse whose dura-tion exceeded 1 msec.

It was reported in many investigations, for example,in refs. 9 and 10' and confirmed by our study that introduc-tion of 1.5% of Ho3 quenched completely the luminescencefrom the 4Iis/2 level. In view of this it would be interesting

to study the influence of the Ho3+ impurity ions on the laseraction in the system under consideration.

Our study showed that Er3+-doped yttrium aluminumgarnet has good spectral and laser properties (rich ab-sorption spectrum of the Er3+ ions, four-level system,high output energy) and good optical, thermal, and mech-anical properties of the matrix. Thus, this material issuitable for lasers emitting the 2.94 n wavelength at roomtemperature.

iU. Robinson and D. P. Devor, Appl. Phys. Lett., 10, 167 (1967).ZS. Kh. Batygov, L. A. Kulevskii, A. M. Prokhorov, V. V. Osiko, A. D.Savel'ev, and V. V. Smirnov, Paper presented at Second Inter. Conf. onLasers and Their Applications, Dresden, 1973 [in Russian].

3L. F. Johnson and H. J. Guggenheim, Appl. Phys. Lett., 23, 96 (1973).4V. A. Gorbachev, V. I. Zhekov, T. M. Murina, V. V. Osiko, B. P.Starikov,and M. I. Timoshechkin, Kratk. Soobshch. Fiz., No. 4, 16, (1973).

SJ. A. Koningstein and J. E. Geusic, Phys. Rev., 136, A726 (1964).6G. M. Zverev, Thesis for Candidate's Degree [in Russian], Institute ofNuclear Physics, Moscow State University (1969).

7G. M. Zverev, G. Ya. Kolodnyi, and A. M. Onishchenko, Zh. Eksp. Teor.Fiz., 60, 920 (1971) [Sov. Phys.-JETP,_33. 497 (1971)].

8R. V. Bakradze, G. M. Zverev, G. Ya. Kolodnyi, G. P. Kuznetsova, L. V.Makarenko, A. M. Onishchenko, N. I. Sergeeva, and Z. I. Tatarov, Zh.Eksp. Teor. Fiz., 53_, 490 (1967) [Sov. Phys.-JETP, 26, 323 (1968)].

9R. V. Bakradze, G. M. Zverev, G. Ya. Kolodnyi, G. P. Kuznetsova, andA. M. Onishchenko, in: Spectroscopy of Crystals [in Russian], Nauka,Moscow (1970), p. 222.

10L. F. Johnson, J. E. Geusic, and L. G. Van Uitert, Appl. Phys. Lett., 7,127 (1965).

1040 Sov. J. Quant. Electron., Vol. 4, No. 8, February 1975 Zharikov et al. 1040