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Spectroscopic properties of Nd3+ doped Sc2O3:LiNbO3 crystal fibers
JOURNAL
OF
LUMINESCENCE ELSEWIER
Journal
of Luminescence
72-74 (1997) 812-815
Spectroscopic properties of Nd3 ’ doped Sc,O, crystal fibers
:
LiNb03
R. Burlot*, R. Moncorgk, G. Boulon LPCML, Uniwrsirt de Lyon I, UMR CNRS 5620. 43 hd du II noaembre 191X, 69622 Villeurhanne Cedex, France
Abstract
Jn this work, we have made a systematic study of the luminescence properties of Nd : Sc203 : LiNb03 crystal fibers grown by using the LHPG technique. We present here the polarized absorption spectra around 800 nm and the polarized emission spectra for the transition 4F3;2 --t ‘I LI ,2. We also have performed frequency doubling measurements versus temperature and site selective spectroscopy. Keywords:
Nd; LiNb03;
Frequency doubling;
Spectroscopy
Self-frequency doubling has been recently demonstrated [l] at a noncritical phase-matching temperature of about 50°C in a 1% Nd: 0.5% Sc203 : LiNbO3 single crystal. This is lower than in Nd : MgO : LiNbOs systems [2]. Moreover it is argued that 1.5 mol% : SC203 : LiNb03 is easier to grow and has a photorefractive damage level comparable to that of 5 mol% : MgO: LiNbOs. So, in order to have more information about that question and to make a more complete comparison with Nd: MgO: LiNbOs, we present here the results of a systematic study of the luminescence properties of 1% Nd : Sc203 : LiNbO3 crystal fibers grown by using the LHPG technique. Nd3+ and SC203 doped LiNbO3 single crystal fibers with nominal molar concentrations of 1% Nd and 1% or 1.5% SC203 were grown in air
*Corresponding author. E-mail:[email protected]
Fax: 72.43.11.30; I.fr.
0022-23 I3/97/$17.00 SC_‘,1997 Eisevier Science B.V. All rights reserved PII SOO22-2313(96)00181-O
by the LHPG (Laser Heated Pedestal Growth) method. The crystal seed was oriented along the a-axis. After annealing in 02, the fibers are clear and single-domain and have a light blue color characteristic of Nd doping. We have grown fibers of about 6 cm long and with diameters of about 600 urn and down to 200 urn. For better handling, they are glued and polished in glass tubes of 1 mm diameter. The spectroscopic and fluorescence data were obtained with standard equipments. For the frequency-doubling measurements, the green light produced was monitored with only a polarizer and a band-pass filter. Site selective spectroscopy has been made at 12 K with the l%Sc203 doped sample. Fig. 1 shows the excitation spectrum of the 4F3i~ level without site selection. Three sites can be clearly identified especially for the Rr Stark level. This has been confirmed by the site selective emission spectra for the transitions 4F3,z -+ 4I9,~ and 4F 3/2 + 41 11~2. Incorporation of SC203 does not
R. Burlot et al. J Journal of Luminescence
72-74 (1997) X12-815
813
5 41g,z
+
4F,,z
WW
Nd-2
Wavelength (run) Fig.
I: Excitation
spectra
of a 1% Nd: 1% Scz03 : LiNbO,
crystal
fiber at 12 K.
6
419,2 -+
813.6 run
Wavelength (run) Fig. 2: RT polarized
absorption
spectra
lead to the appearance of supplementary Nd sites which is not the case of MgO doping [3]. Fig. 2 shows the absorption transition 4I~,~ +(4F~,~ + 2Hs,2) in the region suitable for diode pumping. The lines are broad which permits less stringent diode wavelength control. The maximum is at 813.6 nm in x-polarization and at
of a
1% Nd : 1% SczOJ : LiNb03
crystal
fiber.
808.4 nm in a-polarization. The cross-sections are 4 and 5.5 x 10-20 cm’, respectively. Infrared emission spectra of the metastable level 4F3,2 have been recorded from 850 to 1450 nm after excitation in each of the above-mentioned absorption lines. The RT polarized emission spectra corresponding to the 4F3,z + 4111,~transition are shown
R. Burlot et al. /Journal of‘luminescence
814
72-74 (1997) 812-815
1084.3 nm
Wavelength (nm) Fig. 3: RT polarized
emission
spectra
of a 1% Nd: 1% Sc20,
: LiNbO,
crystal
fiber after excitation
at 808.4 nm in o-polarization.
1140 -
, 0
20
40
I 60
,, 80
,
I 100
120
I 140
,
I 160
,
, 18C
Temperature (“C) Fig. 4: Evolution fibers.
of phase-matching
optimal
wavelengths
with temperature
in Fig. 3 for 808.4 nm excitation in o-polarization. The emission cross-sections have been derived by using the Judd-Ofelt (JO) formalism. The JO parameters are Qz = 2.1 x 10d2’, Q4 = 6.8 x 10e2’ and 526 = 3.8 x lo-*’ cm*. The branching ratio for this transition is B = 0.42 and the radiative lifetime for 4F3,~ is fR = 96 ps. The emission around 1084 nm
for I % Sc203 and 1.5% Sc,O,
: I o/uNd: LiNbO,
crystal
is as intense in 0 as in rc polarization and the G relative intensity increases with the SCZO~ concentration depending on the polarization and the wavelength of excitation. Moreover in a-polarization, the emission lines around 1084 and 1093 nm have about the same intensities which differs with what is found in Nd: MgO: LiNb03 [4]. This is
R. Burlot et al. 1 Journal of Luminescence 72-74 (1997) H/2-815
very important for self-frequency-doubling in a negative crystal such as LiNb03: the fundamental wave must be cr-polarized for efficient doubling. In Ref. [l], self-frequency doubling of the 1093 nm o-polarized laser radiation of Nd3+ in a 1% Nd : 0.5% Sc203 : LiNb03 single crystal has been demonstrated at a non-critical phase-matching temperature of about 50°C. We have completed our study by searching for, in our samples, the optimal wavelength between 1060 and 1150 nm which can be frequency doubled in a temperature domain ranging from about 20 to 180°C. Fig. 4 shows the results for 1% and 1.5% SCZ03 doping. For the emission line at 1093 nm, self-frequency doubling appears to be possible at room temper-
815
ature. If we plot the green output intensity versus the fundamental wavelength, the full widths at half maxima are about 20 and 10 nm, respectively, for 1% and 1.5% SczO3 which means less stringent wavelength and temperature control. More details will be published in a subsequent paper.
References [l] [Z] [3] [4]
J.K. Yamamoto T.Y. Fan et al., E. Camarillo et E. Lallier et al.,
et al., Opt. Lett. 19 (1994) 131 I. JOSA B 3 (1986) 140. al., J. Phys.: Condes. Matter 7 (1995) 9635. Electron. Lett. 25 (1989) 1491.
OF
LUMINESCENCE ELSEWIER
Journal
of Luminescence
72-74 (1997) 812-815
Spectroscopic properties of Nd3 ’ doped Sc,O, crystal fibers
:
LiNb03
R. Burlot*, R. Moncorgk, G. Boulon LPCML, Uniwrsirt de Lyon I, UMR CNRS 5620. 43 hd du II noaembre 191X, 69622 Villeurhanne Cedex, France
Abstract
Jn this work, we have made a systematic study of the luminescence properties of Nd : Sc203 : LiNb03 crystal fibers grown by using the LHPG technique. We present here the polarized absorption spectra around 800 nm and the polarized emission spectra for the transition 4F3;2 --t ‘I LI ,2. We also have performed frequency doubling measurements versus temperature and site selective spectroscopy. Keywords:
Nd; LiNb03;
Frequency doubling;
Spectroscopy
Self-frequency doubling has been recently demonstrated [l] at a noncritical phase-matching temperature of about 50°C in a 1% Nd: 0.5% Sc203 : LiNbO3 single crystal. This is lower than in Nd : MgO : LiNbOs systems [2]. Moreover it is argued that 1.5 mol% : SC203 : LiNb03 is easier to grow and has a photorefractive damage level comparable to that of 5 mol% : MgO: LiNbOs. So, in order to have more information about that question and to make a more complete comparison with Nd: MgO: LiNbOs, we present here the results of a systematic study of the luminescence properties of 1% Nd : Sc203 : LiNbO3 crystal fibers grown by using the LHPG technique. Nd3+ and SC203 doped LiNbO3 single crystal fibers with nominal molar concentrations of 1% Nd and 1% or 1.5% SC203 were grown in air
*Corresponding author. E-mail:[email protected]
Fax: 72.43.11.30; I.fr.
0022-23 I3/97/$17.00 SC_‘,1997 Eisevier Science B.V. All rights reserved PII SOO22-2313(96)00181-O
by the LHPG (Laser Heated Pedestal Growth) method. The crystal seed was oriented along the a-axis. After annealing in 02, the fibers are clear and single-domain and have a light blue color characteristic of Nd doping. We have grown fibers of about 6 cm long and with diameters of about 600 urn and down to 200 urn. For better handling, they are glued and polished in glass tubes of 1 mm diameter. The spectroscopic and fluorescence data were obtained with standard equipments. For the frequency-doubling measurements, the green light produced was monitored with only a polarizer and a band-pass filter. Site selective spectroscopy has been made at 12 K with the l%Sc203 doped sample. Fig. 1 shows the excitation spectrum of the 4F3i~ level without site selection. Three sites can be clearly identified especially for the Rr Stark level. This has been confirmed by the site selective emission spectra for the transitions 4F3,z -+ 4I9,~ and 4F 3/2 + 41 11~2. Incorporation of SC203 does not
R. Burlot et al. J Journal of Luminescence
72-74 (1997) X12-815
813
5 41g,z
+
4F,,z
WW
Nd-2
Wavelength (run) Fig.
I: Excitation
spectra
of a 1% Nd: 1% Scz03 : LiNbO,
crystal
fiber at 12 K.
6
419,2 -+
813.6 run
Wavelength (run) Fig. 2: RT polarized
absorption
spectra
lead to the appearance of supplementary Nd sites which is not the case of MgO doping [3]. Fig. 2 shows the absorption transition 4I~,~ +(4F~,~ + 2Hs,2) in the region suitable for diode pumping. The lines are broad which permits less stringent diode wavelength control. The maximum is at 813.6 nm in x-polarization and at
of a
1% Nd : 1% SczOJ : LiNb03
crystal
fiber.
808.4 nm in a-polarization. The cross-sections are 4 and 5.5 x 10-20 cm’, respectively. Infrared emission spectra of the metastable level 4F3,2 have been recorded from 850 to 1450 nm after excitation in each of the above-mentioned absorption lines. The RT polarized emission spectra corresponding to the 4F3,z + 4111,~transition are shown
R. Burlot et al. /Journal of‘luminescence
814
72-74 (1997) 812-815
1084.3 nm
Wavelength (nm) Fig. 3: RT polarized
emission
spectra
of a 1% Nd: 1% Sc20,
: LiNbO,
crystal
fiber after excitation
at 808.4 nm in o-polarization.
1140 -
, 0
20
40
I 60
,, 80
,
I 100
120
I 140
,
I 160
,
, 18C
Temperature (“C) Fig. 4: Evolution fibers.
of phase-matching
optimal
wavelengths
with temperature
in Fig. 3 for 808.4 nm excitation in o-polarization. The emission cross-sections have been derived by using the Judd-Ofelt (JO) formalism. The JO parameters are Qz = 2.1 x 10d2’, Q4 = 6.8 x 10e2’ and 526 = 3.8 x lo-*’ cm*. The branching ratio for this transition is B = 0.42 and the radiative lifetime for 4F3,~ is fR = 96 ps. The emission around 1084 nm
for I % Sc203 and 1.5% Sc,O,
: I o/uNd: LiNbO,
crystal
is as intense in 0 as in rc polarization and the G relative intensity increases with the SCZO~ concentration depending on the polarization and the wavelength of excitation. Moreover in a-polarization, the emission lines around 1084 and 1093 nm have about the same intensities which differs with what is found in Nd: MgO: LiNb03 [4]. This is
R. Burlot et al. 1 Journal of Luminescence 72-74 (1997) H/2-815
very important for self-frequency-doubling in a negative crystal such as LiNb03: the fundamental wave must be cr-polarized for efficient doubling. In Ref. [l], self-frequency doubling of the 1093 nm o-polarized laser radiation of Nd3+ in a 1% Nd : 0.5% Sc203 : LiNb03 single crystal has been demonstrated at a non-critical phase-matching temperature of about 50°C. We have completed our study by searching for, in our samples, the optimal wavelength between 1060 and 1150 nm which can be frequency doubled in a temperature domain ranging from about 20 to 180°C. Fig. 4 shows the results for 1% and 1.5% SCZ03 doping. For the emission line at 1093 nm, self-frequency doubling appears to be possible at room temper-
815
ature. If we plot the green output intensity versus the fundamental wavelength, the full widths at half maxima are about 20 and 10 nm, respectively, for 1% and 1.5% SczO3 which means less stringent wavelength and temperature control. More details will be published in a subsequent paper.
References [l] [Z] [3] [4]
J.K. Yamamoto T.Y. Fan et al., E. Camarillo et E. Lallier et al.,
et al., Opt. Lett. 19 (1994) 131 I. JOSA B 3 (1986) 140. al., J. Phys.: Condes. Matter 7 (1995) 9635. Electron. Lett. 25 (1989) 1491.