OPTO−ELECTRONICS REVIEW 20(1), 87–90
DOI: 10.2478/s11772−012−0003−4
Pulse generation at 1.5-μm wavelength in new EAT14 glasses doped
with Er3+ and Yb3+ ions
J. MŁYŃCZAK*1, K. KOPCZYŃSKI1, Z. MIERCZYK1, M. MALINOWSKA2, and P. OSIWIAŃSKI3
1Institute
of Optoelectronics, Military University of Technology, 2 Kaliskiego Str., 00−908 Warsaw, Poland
of Micromechanics and Photonics, Warsaw University of Technology, 1 Politechniki Sq.,
00−661 Warsaw, Poland
3Institute of Telecommunications, Teleinformatics and Acoustics, Wrocław University of Technology,
27 Wybrzeże Wyspiańskiego Str., 50−370 Wrocław, Poland
2Institute
The paper describes investigation of pulse laser generation in newly developed EAT14 glasses with the use of MALO satura−
ble absorber. Different initial transmission of the saturable absorbers and different transmission of the output coupler were
investigated. The laser generation was carried out using 976−nm pump wavelength. Comparison of peak powers, slop effi−
ciencies and thresholds was made with a view to choose the best set of glass and saturable absorber for “eye−safe” microchip
laser range−finder. The generated wavelengths by each sample were measured.
Keywords: pulse microchip laser, erbium glass, “eye−safe” laser radiation.
1. Introduction
There are many ways to generate eye−safe radiation at
1.5−μm wavelength [1,2]. One of them is by the use of
glasses doped with erbium and ytterbium ions as active
media. However, there are a few types of these glasses that
can be applied to microchip lasers used for laser range−find−
ers. Well known glasses are QX/Er, QE−7, and QE−7S
glasses, manufactured by KIGRE, which have been most
often applied to lamp and diode pumped laser heads. Also,
at the General Physics Institute at Russian Academy of
Sciences in Moscow, two types of erbium glasses were
developed. One of them is concentrated Yb−Er laser glass
[3], and the other one is strong erbium laser glass (SELG),
especially developed for microchip laser applications [4].
As a result of this, there are still intensive researches into
developing new, more efficient, active media.
Recently, new type of glasses EAT14 doped with Er and
Yb ions were manufactured by the CLaser Photonics seated
in Shanghai [5]. Despite the manufacturer’s claim that they
are characterized by very good parameters there is still lack
of paper in the literature concerning laser generation with
their use. The only paper concerning investigation of cw
generation in these glasses is Ref. 6. This implies the desi−
rability of research into pulse generation using these glasses
as active media.
In this paper we present investigations of pulse genera−
tion in EAT 14 glasses pumped by 976−nm laser diode.
MgAl2O3 crystals doped with Co ions with different initial
*e−mail:
[email protected]
Opto−Electron. Rev., 20, no. 1, 2012
transmission and different transmission of the output cou−
pler deposited on them were used as saturable absorbers.
The attempt to find the best combination of glasses, initial
transmission of the saturable absorber, and the transmission
of the output coupler for “eye−safe” microchip laser range−
−finder was made.
2. Experiment and discussion
Three samples of EAT14 glasses with different concentra−
tion of dopants and thickness were examined. The choice of
the glasses was made on the basis of investigation presented
in Ref. 4 which showed that these samples are characterized
by good parameters. The samples had 6−mm diameter and
they are listed below:
a) EAT14−4: Yb 2 × 1021 cm–3, Er 1 × 1020 cm–3, thickness
1 mm,
b) EAT14−7: Yb 2 × 1021 cm–3, Er 0.5 × 1020 cm–3, thick−
ness 1.5 mm,
c) EAT14−8: Yb 2 × 1021 cm–3, Er 1 × 1020 cm–3, thickness
1.5 mm.
To achieve efficient laser generation, appropriate coa−
tings were deposited on the glass samples. As shown in
Fig. 1, dichroic input mirrors (AR@975 nm, HR@1535
nm) were deposited on one side of the glass samples and
AR@1535 nm coatings on the other.
As passive Q−switches, MgAl2O3 crystals with different
initial transmission were used. In this case, AR@1535 nm
coatings were deposited on one side and partially transmit−
ting output mirrors at 1535 nm wavelength on the other, as
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Pulse generation at 1.5−μm wavelength in new EAT14 glasses doped with Er 3+ and Yb3+ ions
Fig. 1. Glass sample prepared for laser generation.
Fig. 2. Saturable absorbers prepared for laser generation.
is shown in Fig. 2. The samples had 6−mm diameter and
they are listed below:
a) MALO−1: To = 97%, Toc = 98.5%, thickness 0.258 mm,
b) MALO−2: To = 96%, Toc = 98.5%, thickness 0.346 mm,
c) MALO−3: To = 99%, Toc = 97.5%, thickness 0.085 mm,
d) MALO−4: To = 98%, Toc = 97.5%, thickness 0.171 mm,
e) MALO−5: To = 97%, Toc = 97.5%, thickness 0.258 mm,
f) MALO−6: To = 96%, Toc = 97.5%, thickness 0.346 mm,
g) MALO−7: To = 99%, Toc = 96.5%, thickness 0.085 mm,
h) MALO−8: To = 98%, Toc = 96.5%, thickness 0.171 mm,
i) MALO−9: To = 97%, Toc = 96.5%, thickness 0.258 mm,
j) MALO−10: To = 96%, Toc = 96.5%, thickness 0.346 mm,
k) MALO−11: To = 99%, Toc = 95.5%, thickness 0.085 mm,
l) MALO−12: To = 98%, Toc = 95.5%, thickness 0.171 mm,
where To is the initial transmission of the saturable absorber
and Toc is the transmission of the output coupler.
Laser investigations were carried out in experimental
setup presented in Fig. 3. For pumping laser, the diode
LIMO25−F100−LD976 generating at 976 nm was used. The
length of the laser resonator was determined by the length of
the active media and the length of the saturable absorber.
The dependence of the output power on the incident pump
power was examined in quasi−cw (duty−cycle 50%) pump−
ing mode without cooling of the active media. Generation
was achieved in all combinations of the active media and
saturable absorbers.
The operation of the laser range finder with adequate
detection system implies that the pick power Pp of the laser
pulse should be at least equal to 1 kW to efficiently measure
the distance up to several kilometres. Thus, in Table 1 the
results of investigations of the best combinations of the
active media and saturable absorbers are presented.
As it can be seen from the table, the highest peak power
is achieved with the same saturable absorbers with three dif−
ferent glasses. It means that these passive q−switches were
characterised be the close to optimal transmission of the out−
put mirror and the initial transmission of the saturable
absorber. The low output power of the other combinations
of the samples might be explained by the low accuracy of
the transmission of the coatings deposited on the active
Fig. 3. Experimental setup for investigations of laser generation.
Table 1. Results of investigations of the best combinations of the active media and saturable absorbers.
MALO−3
EAT14−4
EAT14−8
MALO−9
96.5
MALO−11
97.5
To (%)
99
99
98
97
99
Pp (kW)
2.02
1.02
1.25
2.22
0.78
Tp (ns)
5.4
6.0
5.6
4.9
7.1
95.5
14.04
12.11
4.02
7.8
6.5
Threshold (mW)
218
318
582
243
412
Pp (kW)
1.06
0.75
0.83
1.92
0.72
Tp (ns)
7.2
7.2
8.8
5.4
8.5
Slop efficiency (%)
9.27
3.52
4.31
8.01
7.05
Threshold (mW)
216
416
432
238
385
Pp (kW)
4.01
1.11
1.57
2.50
0.82
Tp (ns)
6.0
7.2
8.0
5.0
8.2
18.19
10.64
12.47
13.05
9.85
216
257
390
229
356
Slop efficiency (%)
Threshold (mW)
88
MALO−8
Toc (%)
Slop efficiency (%)
EAT14−7
MALO−7
Opto−Electron. Rev., 20, no. 1, 2012
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media and the saturable absorbers which was 2%. The
desired accuracy to achieve efficient generation is at least
0.5%, thus it means that the other q−switches might have
had the coatings characterized by transmission which was
much different from the optimal one. If the accuracy of the
transmission of coatings is not close to 0.5%, the best solu−
tion to find the close to optimal transmission of the output
mirror and the initial transmission of the saturable absorber
is a process of trial and error.
The pulse duration Tp for each combination of the sam−
ples amounts to several ns but the shortest are for MALO−3
and MALO−9. Also, the highest peak power is for the same
saturable absorbers. The pulses generated by EAT14−4 are
little longer then these generated by EAT14−7 and
EAT14−8. It is caused by the length of the active media
which defines the length of the resonator. The shortest reso−
nator implies the shortest pulse duration. The exemplary
6−ns pulse generated by microchip laser EAT14−8/MALO−3
is shown in Fig. 4.
Fig. 5. Output power vs. pump power for the EAT14−8 glass for five
saturable absorbers.
AQ6319. The lasers generated at only one longitudinal
mode at 1535 nm wavelength. The exemplary spectrum
generated by microchip laser EAT14−8/MALO−3 is shown
in Fig. 6.
Fig. 4. Exemplary pulse generated by microchip laser EAT14−
−8/MALO−3.
Fig. 6. Generated spectra by microchip laser EAT14−8/MALO−3.
Table 1 shows that the main lasing parameter, like slope
efficiency for different combination of samples, ranges
from several percent to over 18%. Also, the threshold is
between 216 mW and 582 mW. These two parameters
strongly depend on the transmission of the output coupler
and the initial transmission of the saturable absorber. The
highest slop efficiency 18.19% and the lowest threshold 216
mW as well as the peak power over 4 kW was achieved for
the combination of the glass EAT14−8 and MALO−3
saturable absorber.
Comparing the investigated glasses, one can see that the
best one is EAT14−8 and it is the same as for cw generation
presented in Ref. 6.
In Fig. 5, the output power vs. pump power for the
EAT14−8 glass for the five saturable absorbers is presented.
For each of these microchip lasers, the generation spec−
trum was examined using the optical spectrum analyzer
Opto−Electron. Rev., 20, no. 1, 2012
3. Conclusions
The results of the investigations presented in this paper
show that it is possible to build very efficient microchip
laser with peak power up to 4 kW using two separate sam−
ples of active media made of EAT14 glass and saturable
absorber MgAl2O3. It is not so easy to deposit the appropri−
ate coatings with high accuracy on the samples so as to effi−
ciently generate the pulse radiation. However, from the
properly prepared set of samples, one can find the right
combination. It was also proved that the best laser glass
seems to be EAT14−8 glass with concentration of dopants of
Yb 2 × 1021 cm–3 and Er 1 × 1020 cm–3 and the thickness of
1.5 mm. The results of the investigations shown in this
paper made possible to build microchip laser head for laser
range finder application.
89
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Pulse generation at 1.5−μm wavelength in new EAT14 glasses doped with Er 3+ and Yb3+ ions
References
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Opto−Electron. Rev., 20, no. 1, 2012
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