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POLARIZATION PROPERTIES AND NEW 3 µm LASER LINES IN YAlO3 : Er
S. Schnell, M. Stalder, W. Lüthy
To cite this version:
S. Schnell, M. Stalder, W. Lüthy. POLARIZATION PROPERTIES AND NEW 3 µm LASER LINES IN YAlO3 : Er. Journal de Physique Colloques, 1987, 48 (C7), pp.C7-371-C7-373.
�10.1051/jphyscol:1987789�. �jpa-00227093�
JOURNAL DE PHYSIQUE
Colloque C7, supplement au n012, Tome 48, decembre 1987
POLARIZATION PROPERTIES AND NEW 3 pm LASER LINES I N YA10,:Er
S. SCHNELL, M. STALDER and W. LUTHY
Institute of Applied Physics, University of Bern, Sidlerstrasse 5 , CH-3012 Bern, Switzerland
Laser emission from YA10, crystals is polarized because of the ortho- rombic DIS2,., (Prim-) unit cell and the monoclinic C,Er3' site symmetry [I]. In Erbium doped laser material the upper laser level 4111,2 con- sists of 6 and the lower level 41,3,z of 7 Stark splitted sublevels.
Therefore 42 optical transitions exist. Until now in YA10,:Er crystals at 300 K lasing has only been observed at the three lines of A = 2.73 um, 2.79
urn
and 2.92 um [2,31.The various laser lines can be differently polarized. It is possible to excite six more laser lines with the use of an intracavity pola- rizer and selectively absorbing filters.
First the polarization properties of the YA103:Er laser are described.
Laser rods with their to the crystallographic b-direction and with dopant 10 % and 50 % as well as a rod with the axis
1
a and an Er concentration of 20 % have been used in the expe- rimen.
The experimental arrangement is shown in Fig. l.M D Fig. 1:
M1 L B M a F Experimental arrangement.
M,,Mz: dielectric resonator mirrors;B: Brewster plate;
L: laser head with water cooled helical flashlamp and YA10,:Er rod; F: lens; M:
20 cm grating monochromator;
D: InAs photodiode; 0: oscil- loscope.
The polarization is selected by an intracavity Brewster window made from sapphire. The Brewster wjndow has practically no losses for p- polarization and 43 % loss per round trip for s-polarization. This is enough to suppress s-polarized laser emission.
In our experiment the laser rod is rotated with respect to the plane of incidence of the Brewster plate. The threshold is measured at dif- ferent angles for each wavelength. The values are indicated in Figs 2.3-c. The solid lines in these Figs represent a fit of the measured values completed to 360". The threshold is measured in intervals of
5". The arrows termed by a and c indicate the position with a-axis and
c-axis respectively parallel to the plane of incidence. The radius is inversely proportional to the lasing threshold; the circles denoted by 1,2 and 4 represent the values of 1-,2- and 4-fold threshold pump energy. From the Fig.2a it can be seen that only one laser line at 2.92 um is found and that minimum laser threshold results in an arran- gement wlth the c-axis parallel to the plane of incidence. In the case
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987789
C7-372 JOURNAL DE PHYSIQUE
of Fig.2b the lowest threshold is found for the 2.73 pm emission pola- rized
11
c. 2.79urn
emission occurs with a polarization11
b and 2.92 pm emissionI
c. In the arrangement of Fig. 2c 2.79 pm emission has not been observed, however, a new wavelength at 2.76 pm has been found with minimum threshold for a polarization of about 2 30- from the a-axis.Fig. 2a: Fig. 2b:
b--rod with 50 % dopant a-rod with 20 % dopant concentration. concentration.
The wavelength is The wavelengths are labelled with labelled with
for 2.92 vm, for 2.92 pm, A for 2.79 um and
for 2.73
urn.
Fig. 2c:
b-rod with 10 % dopant concentration.
The wavelengths are labelled with
for 2.92 pm, A for 2.76
urn
and a for 2.73 urn.The measurement of the five new laser lines is performed by the same experimental arrangement. The laser emission is analyzed with a 115 cm monochromator equipped with a 600 g/mm grating with a resolution of about
+
0.1 nm.From Fig. 2c it can be seen that for a polarization
1
a laser emission at 2.92urn
is suppressed. In addition laser emission at 2.73 pm and 2.76 pm can be avoided by placing absorbing filters into the reso- nator. The transmission of suitable filters as a function of wave- length is shown in Fig. 3.Fig. 3:
Transmission of selective filters in the wavelength range of 2,6 um to 2.95
urn.
Mica. Solid line: Muscovite (s) with a thickness of about 30 pm, dashed line: Muscovite ( d ) in 90' ori- entation, dotted line, phlogopite with a thickness of about 30 pm.In muscovite a very sharp absorption band near the wavelength of 2.73 vm is found. Phlogopite can be used as an optical high-pass-filter discriminating at about h = 2.72 urn. Since the optical thickness of the birefringent muscovite crystals can be varied by rotating the optical axis with respect to the polarization, the transmission maxima of the filter can be changed. From Fig. 3. it is seen that depending on the optical axis parallel or perpendicular to the polarization the maximum at 2.814 vm is switched to 2.840 prn leading to laser action at wavelengths of 2.82 vm or 2.84 vm respectively. A "Suprasil I" quartz plate can be used a s an absorbing filter for the strong laser lines at 2.73 vm, and 2.76 urn or 2.79 vm. The wavelengths below 2.72 pm can be absorbed by an acetate foil.
With these elements it is possible to suppress the most prominent laser lines in favour of new laser transitions between the aI,,,2
- >
a11,,2 manifolds.
The tentative assignement of the lines is shown in Fig. 4.
2.7307pm 2.7067pm 2.8200pm
X6 10400 X5 10380 X4 10364 X3 10320 X2 10301 XI 10282
Fig. 4:
Y 7 6ae, Stark splitting of the aI,,,, and
6817 41,3,2 levels lcm-I1 with the observed
6770 laser transitions and their tentative
y 4 6714 assignement. The three transitions at
~3 6666 the right hand side are known [2,31,
Y2 6640 the six transitions at the left hand
Y l 6601 side are described in [ 4,5 1.
In conclusion we have shown that simultaneous laser oscillation can be achieved on three different lines of the 41,,,2 - > 4113,2 manifolds at room temperature. The polarization properties of a 50% b-rod, a 20% a- rod and a 10% b-rod have been measured. We have shown that it is possible to obtain laser action at 300 K on 9 different wavelengths ranging from 2.71 nm to 2.92 nm. Wavelength selection is achieved with sapphire Brewster plates and selectively absorbing filters.
References
[11 R. Diehl and G. Brandt, Mat. Res. Bull. 1_0 85-90 (1975)
(21 A . A . Kaminskii, V.A. Fedorov, A.O. Ivavov, I.V. Mochalov,
and L.I. Krutova, Sov. Phys. Dokl. 27 (9) 725-727 (1982)
[31 A . A . Kaminskii, Sov. Phys. Dokl.
22
(12) 1039-1041 (1982)[41 M. Stalder, W. Liithy, Opt. Commun.
