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The work was presented at Laser Optics'95, Solid State Lasers, 27 June - 1 July 1995, St. Petersburg, Russia
see also:....S.M. Kaczmarek, Z. Mierczyk, K. Kopczyński, Z. Frukacz, I. Pracka, T. Łukasiewicz, "Comparison of Pr3+:YAG and Pr3+:SLGO Lasers", Optoelectronica 4(1), (1996), pp. 41-45, ROMANIA, Bukarest
and: Z. Mierczyk, S.M. Kaczmarek, K. Kopczyński, Z. Frukacz, I. Pracka, T. Łukasiewicz, "Spectroscopic and laser properties of different materials doped with Pr3+ ions", Acta Phys. Pol. A, vol. 90 (2) (1996) pp.407-410
Pr3+: doped YAG and SLGO laser rods
Sławomir M. Kaczmarek1, Zygmunt Mierczyk1, Krzysztof Kopczyński1
Zygmunt Frukacz2, Izabella Pracka2, Tadeusz Łukasiewicz2
Proc. SPIE, Vol. 2772 (1995), pp. 102-107, 0-8194-2157-X/96/$6.00
1. Institute of Optoelectronics , Military University of Technology, 2 Kaliski Str.
00-908 Warsaw, Poland
2. Institute of Electronic Materials Technology, 133 Wólczyńska Str., 01-919 Warsaw, Poland
ABSTRACT
Examined praseodymium doped crystals with 1at. % of Pr3+ ions for YAG and SrLaGa3O7 (SLGO) hosts were produced using Czochralski method. The luminescence for the range of 200 - 800 nm and absorption spectra for a wide range of 200-6000 nm , for Pr3+:YAG and Pr3+:SLGO crystals have been measured. It was stated that for praseodymium doped YAG and SLGO crystals, the strongest peaks of luminescence occur at 0.489 and 0.502 mm and the strongest peaks of absorption occur at 0.44 - 0.5 and 0.58 - 0.62 mm bands. A free - running laser emission of l = 0.62 m m radiation for both types of crystals Pr:YAG and Pr:SLGO for two different transmissions of output mirrors have been obtained.
Keywords: doping, laser crystals, optical properties, lasing properties, UV radiation sensitivity, absorption, luminescence.
1. INRODUCTION
Trivalent praseodymium in crystals is a
well known ion which have a very rich emission spectrum extending from
ultraviolet (UV) to infrared (IR)1, 2.
Because of the energy level structure 3
and suitable lifetimes of the excited states, Pr3+
systems are specially attractive as an active materials for lasers emitting in
short wavelength range. The CW stimulated emission at several orange and red
wavelengths in Pr3+
doped perovskite (YAP) has been reported in 4, 5.
Simultaneous blue and orange wavelengths lasing in Pr3+ doped
YAP and YAG crystals have been observed in 6.
In this lecture several topics relating to the short wavelength solid state
lasers: YAG and SLGO doped with Pr3+
(0.62mm)
are discussed.
2.
EXPERIMENTAL RESULTS
Samples from Pr:YAG and Pr:SLGO crystals
with diameters of 10 mm and thickness of 1 - 2 mm, both sides optically polished,
were cut out from the most homogeneous parts of the crystals (examined with
Mach-Zehnder interferometer system) made in the Institute of Electronic
Materials Technology. These samples has undergone spectroscopic and luminescence
investigations.
In order to determine the absorption coefficient
in dependence on wavelength, the samples transmission was measured using the
following spectrophotometers:
(i)
- LAMBDA - 2 of PERKIN-ELMER in the spectral range of 200 - 1100 nm,
(ii)
- ACTA VII of BECKMAN in the range of 1100 - 1400 nm and
(iii)
- Fourier spectrophotometer FTIR 1725 of PERKIN-ELMER in the range of 1400nm to
25 mm.
Dispersion of the absorption coefficient was calculated from transmission
measurements with the consideration of multiple reflections inside a sample.
Luminescence investigations were carried
out using PERKIN-ELMER LS - 5B spectrofluorimeter .
For
the typical laser head, rods of 3 mm in diameter and about 40 mm in length were
investigated with reference to their laser features. The above investigations
were carried out using plane-parallel laser resonator of length 23 cm, and
output mirrors of 21% and 35% transmition at 0.619
mm.
The laser head consisted of a single linear xenon flashlamp of 4 mm
in diameter and a reflector made of gold-covered brass. The duration of
flashlamp pulse was equal to 150
ms
and the pump energy was changed from 4 to 40 J.
2.1
Optical investigations
The results of spectroscopic investigations
are shown in Figs 1-4. It can be seen that intensity of absorption lines for
Pr:YAG crystals is larger than for Pr:SLGO ones. These lines are placed in the
same region of absorption spectrum. An average optical density is greater for
Pr:SLGO crystals. The absorption threshold for both crystals, appear at 300 nm
and lattice absorption is observed above 5500 nm.
The results of luminescence measurements
are shown in Figs 5a and b. It was stated that
for Pr3+:YAG
crystals, the strongest peaks of luminescence occur at 0.489, 0.502, 0.565 and
0.620
mm
. For Pr3+:SLGO crystals
the strongest peaks of luminescence are: 0.489, 0.503, 0.616 and 0.645 mm.
Fig.6 presents results of absorption
measurements of Pr:YAG crystal (thin sample) after UV excitation with xenon pump
lamp - 10 pulses of 42.2 J energy with time interval equal to 15s between them.
From this figure it results that Pr:YAG crystal is UV radiation sensitive and
that there are unstable colour centres after UV radiation. Time quenching
interval for transmission of these centres is 1%/1000s.
2.2
Lasing investigations
A free-running laser emission
of
=0.62 m
m
radiation for both types of crystals and for two different, above mentioned
transmissions of output mirrors have been obtained. The emitted laser radiation
energy was measured by means of Universal Radiometer Rm6600 of Laser Precision
Co. with RJP-735 probe. Simultaneously, the lamp pulses were observed on the
Tektronix oscilloscope using a high-sensitivity Si photodetector. UV radiation
was eliminated by using sodium glass filters inside of laser cavity. The results
of lasing measurements can be seen in Fig. 7. Thresholds of laser emission for
Pr3+:YAG
crystals were smaller than for Pr3+:SLGO
ones (10 J and 20 J respectively). Efficiencies of these lasers were 0.24% and
0.2% respectively.
For both types of crystals and for some
greater pump energies, the saturation of laser emission was noticed. In the case
of Pr3+:SLGO
crystal there were observed coloured centers generated by illuminating the rod
with xenon flashlamp. To avoid the parasite heating of the laser rod and
variations of its laser characteristics, the cut-off filters made of
sodium glass (cut-off wavelength equal to 350 nm) were used.
3.
CONCLUSIONS
Intensity of absorption lines for Pr:YAG
crystals is larger than for Pr:SLGO ones (the same doping level of 1at.%). These
lines are placed in the same region of absorption spectrum. Optical density is
greater for Pr:SLGO crystals. Short-wave edge of absorption is the same for both
crystals and equal to 300 nm. Lattice absorption for both crystals is equal to
about 5300 - 5800 nm.
A free-running laser emission of
=0.62 m
m
radiation for both types of crystals Pr:YAG and Pr:SLGO for two different
transmissions of output mirrors has been obtained. Thresholds of laser emission
for Pr3+:YAG
crystals were smaller than for Pr3+:SLGO
ones (10 J and 20 J respectively). Efficiencies of these lasers were 0.24% and
0.2% respectively. For both types
of crystals and for some greater pump energies, the saturation of laser emission
was noticed. In the case of Pr3+:SLGO
crystal there were observed coloured centers generated by illuminating the rod
with xenon flashlamp.
4.
REFERENCES
1.
A.A. Kaminskii, "Laser crystals, their physics and properties",
Springer-Verlag, Berlin-Heidelberg-NY, 1981.
2.
E.G. Gumanskaya, M.V.Korzhik, S.A.Smirova, V.B. Pavlenko and A.A. Fedorov,
"Interconfiguration luminescence of Pr ions in YAG and YAP single crystals",
Opt. Spectrosc., vol.72, pp.86-89,
January 1982.
3.
H.J. Eichler and B. Liu, "Gepulster LiYF4:Pr-laser",
Technische Universitat Berlin, Optisches Institut, July 1993
4.
A.Bleckmann, F.Heine, J.P.Meyn, K.Peterman and G.Huber, "CW-lasing of
Pr:YAlO3
at room temperature", Advanced solid-state lasers, paper ATuB1-1,
pp.164-166, February 1993
5.
A.Bleckmann, F.Heine, J.P.Meyn, T.Danger, K.Peterman and G.Huber, "Continuous-wave
lasing of Pr:YAlO3
at room temperature", CLEO'93, Baltimore, CThF2, May 1993
6. M.Malinowski, M.F.Joubert, R.Mahiou and B.Jacquier, "Visible laser emission of Pr in various hosts", Laser M2P Conference, Lyon, December 1993
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