- Email: [email protected]
Investigation of Nd3+ ions spectroscopic and laser properties in SrF2 fluoride single crystal
Optical Materials 34 (2012) 799–802
Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Investigation of Nd3+ ions spectroscopic and laser properties in SrF2 fluoride single crystal O.K. Alimov, T.T. Basiev, M.E. Doroshenko ⇑, P.P. Fedorov, V.A. Konyushkin, A.N. Nakladov, V.V. Osiko Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow, Russia
a r t i c l e
i n f o
Article history: Received 30 March 2011 Received in revised form 2 November 2011 Accepted 8 November 2011 Available online 26 December 2011 Keywords: Rare-earth doped fluoride Diode laser pumping Optical centers spectroscopy
a b s t r a c t The laser properties of SrF2:Nd3+ crystal with neodymium ions concentration of 0.5 at.% were investigated under diode laser pumping. Using temperature tuning of laser diode pumping wavelength two different lines centered at about 1037 nm and 1044 nm attributed to oscillation of different optical centers were obtained. The maximum lasing slope efficiency of 37% was obtained. The absorption and fluorescence spectra of different individual and clustered Nd3+ ions optical centers were observed depending on Nd3+ concentration. The lifetimes of the high symmetry L-centers were measured and found to be two orders of magnitude longer than that for clustered M-centers at room temperature. The lifetimes of M-centers at different temperatures were measured and microparameter of ion–ion interaction in Nd-pairs was determined. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Neodymium doped fluoride crystals attracts growing attention for development of diode-pumped lasers due to specific spectroscopic properties of Nd3+ ions including rather broad absorption and fluorescence spectra together with long radiative lifetime of 4 F3/2 state. Trivalent rare-earth ions in fluorides are known to form different optical centers due to heterovalent substitution of divalent cations and different forms of charge compensation. The set of optical centers usually depends on the type of rare-earth ions, their concentration and fluoride host. Existence of wide range of fluoride solid-solutions also allows to influence the process of optical centers formation and thus manipulate the spectroscopic and oscillation properties of rare-earth ions [1]. Additional advantage of these materials that they could be obtained in the form of high optical quality laser ceramics [2,3]. 2. Experimental setup To investigate the laser properties of neodymium-doped single crystals a setup based on a PUMA laser diode with the maximum average output power of 15 W was used. The laser diode was fiber coupled with the fiber core diameter of 120 lm. The pump radiation was focused inside the active crystal by single spherical lens. The output energy was measured using EPM-2000 energy meter. The oscillation spectra were measured by LRL-005 wavelength meter. ⇑ Corresponding author. Tel.: +7 499 1350318; fax: +7 499 1350270. E-mail address: [email protected] (M.E. Doroshenko). 0925-3467/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2011.11.010
For spectroscopic measurements pulsed tunable Ti:sapphire and dye lasers pumped by second harmonics of Q-switched YAG:Nd laser were applied. 3. Laser properties of SrF2:Nd3+ crystal under LD pumping The oscillation properties of the crystals were studied using the cavity formed by a flat dichroic mirror which was deposited to one side of the crystal with antireflection coating on the other and a curved output mirror with 50-mm curvature placed at about 35 mm distance from the flat dichroic mirror. The reflectivity of the output mirror was changed to optimize the laser output. In Fig. 1, the input–output characteristics of the laser based on SrF2:Nd3+ crystal is demonstrated. The length of the SrF2:Nd3+ crystal used was 10 mm so the lens with the focal length of 12 mm was used to form the pump waist inside the crystal. To optimize the pump profile the distance from the lens to the fiber end was optimized to be about 1.8 of the lens focal length. As can be seen from the figure the slope efficiency of 27% was obtained in case of 95% reflectivity of the output mirror. To optimize the output different focusing lenses were tested. In Fig. 2, the input–output characteristics of SrF2:Nd3+ crystal are shown for different focal lengths of the focusing lens. As could be seen from the figure maximum output was realized for lens with focal length of 8 mm where slope efficiency of 29% was demonstrated. For each case the distance from the lens to the fiber end was optimized to obtain the most effective matching between the pump and cavity oscillating mode. Measurements of the oscillation spectrum showed that in case of 789 nm pumping and output mirror reflectivity of 95% for low
800
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
1.5
Output Power, W
1.0
Output Power, W
1.5
SrF2 :Nd 3+
R=95% η sl =27%
τ pump =3 ms, f=10Hz f=12 mm
R=85% η sl =13%
3+
SrF2 :Nd 1.0
f=10Hz; τ pump =3 ms
0.5
R=95% λ exc =789nm
0.0 0.0
0.5
1.5
3.0
4.5
6.0
Absorbed Power, W 0.8 0.0 0.0
1.5
3.0
4.5
0.4
6.0
Absorbed Power, W
0.0
Fig. 1. Input–output characteristics of SrF2:Nd3+ crystal for different reflectivities of the output mirror.
0.8
pumping level oscillations occur only at the wavelength of 1037 nm. For higher pumping levels additional oscillating line centered at about 1044 nm appears as can be seen in Fig. 3. For output mirror reflectivity of 85% oscillations only at 1037 nm line were observed. The oscillation spectrum of SrF2:Nd3+ crystal was also found to depend on the laser diode (LD) pumping wavelength. In Fig. 4, the laser diode oscillation spectra temperature tuning with respect to absorption spectra of SrF2:Nd3+ crystal is demonstrated. The shift of the pumping wavelength from 789 nm to 793 nm (two local maxima at the SrF2:Nd3+ absorption spectrum) resulted in the strong change between the two oscillating lines intensity distribution as can be seen in Fig. 4. The plot of the normalized oscillating line intensities versus the laser diode pumping wavelength (for maximum pumping level) is shown in Fig. 5. As can be seen from the figure the shift of pumping wavelength from 789 nm to 793 nm results in completely inverse ratio in the oscillating lines intensities. Input–output characteristics on SrF2:Nd3+ crystal pumped in absorption maximum of 796 nm is shown in Fig. 6 where slope efficiency as high as 37% was achieved. For this pumping wavelength the intensity of both oscillating lines (1037 nm and 1044 nm) was practically equal. 4. Spectroscopic properties investigation Fluorides of SrF2 type doped with trivalent rare-earth ions are known to form different optical centers due to several possibilities
1.5
Output Power, W
SrF2:Nd
1.0
3+
R=95% f=10Hz, τ pump =3ms
f=8 mm η sl =29% f=12 mm ηsl =27%
0.5
f=65 mm ηsl =11% 0.0 0.0
1.5
3.0
4.5
6.0
Absorbed Power, W Fig. 2. Input–output characteristics of SrF2:Nd3+ crystal for different focal lengths of the lens.
Intensity
0.4 0.0 0.8 0.4 0.0 0.8 0.4 0.0 1036
1038
1040
1042
1044
Wavelength, nm Fig. 3. Oscillation spectrum of SrF2:Nd3+ crystal for different pumping levels.
of excessive charge compensation. With increased concentration of rare-earth ions also different clusters are formed. These different types of optical centers are characterized by different spectroscopic properties. The room temperature fluorescence spectrum of SrF2:Nd3+ crystal is characterized by two maxima at 1037 nm and 1044 nm. To investigate the contribution of different optical centers to the fluorescence spectrum and maxima the time resolved fluorescence spectra of SrF2:Nd3+ crystal were measured shown in Fig. 7. In this experiment pulsed tunable titanium sapphire laser pumped with nanosecond second harmonic YAG:Nd pulses was used as excitation source. As could be seen from the figure fluorescence spectra for long lifetime and short lifetime selection are different which corresponds to fluorescence of highsymmetry tetragonal L-centers and paired rhombic M-centers respectively. To determine the contribution of different optical centers to different oscillation lines the decay curves were measured for the excitation wavelengths of 789 nm and 793 nm. The measured decay curves are presented in Fig. 8. As could be seen from the figure for 789 nm excitation contribution of high symmetry tetragonal optical centers with long lifetime of about 1.0 ms to fluorescence at 1037 nm prevails. For 793 nm excitation the contribution of M-clustered centers with short lifetime of about 17.5 ls is sufficiently increased especially for 1044 nm fluorescence in accordance with the obtained fluorescence spectrum of clustered centers. As also follows from Fig. 9 the decay curve in SrF2:Nd3+ crystal could be described by two exponents which corresponds to two types of optical centers with lifetimes of 1 ms for high symmetry tetragonal optical L-centers and 17.5 ls for clustered M-centers.
801
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
5
1.5
Laser Diode spectrum
3+
SrF2 :Nd
0.5
0.0 780
785
790
795
800
805
f=12 mm 3
R=95% λex =796 nm
2
ηsl =37%
1
Wavelength, nm
0
λ pump =789 nm Intensity
3+
τ pump =3 ms, f=10Hz
4
1.0
Output Power, W
Absorption
SrF2 :Nd
0
2
4
0.8
6
8
10
12
Absorbed Power, W Fig. 6. Input–output characteristics of SrF2:Nd3+ crystal pumped in absorption maximum.
0.4
0.0
0.8
1038
1040
1042
1044
1046
λ pump =793 nm
SrF2 :Nd 3+
0.4
L-centers 0.0 1036
1038
1040
1042
1044
1046
Wavelength, nm
Intensity
Intensity
1036
M-centers
Fig. 4. Dependence of the SrF2:Nd3+ crystal oscillation spectrum on pumping wavelength.
1000
1020
1040
1080
110 0
λ osc =1037nm
Fig. 7. Time resolved fluorescence spectrum of Nd3+ in SrF2 crystal.
0.8 0.6
1
0.4
SrF 2:Nd
λ osc =1044nm 0.2 0.0 788
3+
Mostly L-centers λex=789 nm
0.6
λreg=1037 nm
0.4 790
792
794
796
798
LD Pumping Wavelength, nm
I/Io
Normalized Intensity
1060
Wevelength, nm
1.0
Fig. 5. Normalized relation between oscillation lines intensities for different pumping wavelengths.
0.2
The spectroscopic properties of Nd3+ ions optical centers in SrF2 crystal were also investigated using excitation with Rodamin 6G 2 tunable dye laser via excitation of 4I9/2– G7/2; 4G5/2 transition. As follows from [4] the absorption lines of clustered Nd3+ M-centers 2 could be separated in absorption spectrum at 4I9/2– G7/2; 4G5/2 transition especially at liquid nitrogen temperature. The absorption spectrum at 300 K and 77 K temperature is shown in Fig. 10 with the M-centers absorption line marked with an arrow. For both cases the decay curve was double exponential. For room temperature the short component lifetime was measured to be 17.5 ls while long one the lifetime was 1 ms which is the same value as was obtained for M-centers and L-centers above
0.1 0.0
M+L - centers λex=793 nm λreg=1044 nm 0.5
1.0
1.5
2.0
Time, ms Fig. 8. Decay curves of Nd3+ ions in SrF2 for different excitation and registration wavelengths.
for Ti:sapphire excitation. For liquid nitrogen temperature the short decay component demonstrates increase both in relative (to long component) intensity and duration. The measured decay time for short component increased from 17.5 ls to 115 ls while decay time for long component stayed unchanged (see Fig. 11).
802
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
1.0
SrF2 :Nd
0.8
5. Conclusions
3+
Different Nd3+ optical centers in SrF2 crystal were determined and their absorption and fluorescence spectra and lifetimes were measured. Oscillation spectrum of Nd3+ ions in SrF2 crystal was found to change with laser diode pumping wavelength depending on excitation of different Nd3+ optical centers. Laser oscillations of Nd3+ ions in SrF2 crystal under laser diode pumping were obtained with slope efficiency up to 37%.
I/Io
0.4
τ 2=1 ms 0.2
τ 1 =17.5 μs
Acknowledgments
0.1 0
20
40
60
80
100
120
140
160
Time, μs Fig. 9. Double exponential decay curve of Nd3+ ions in SrF2 crystal for high symmetry L-centers and clustered M-centers.
9/2
--> 2 G
7/2
;4 G
M-centers
5/2
Absorption
4I
T=300K
T=77K
560
570
580
590
Wavelength, nm Fig. 10. Absorption spectra of Nd3+ ions at 4I9/2–2G7/2; 2G5/2 transition at 300 K and 77 K.
1
3+
SrF2:0.5%Nd
λexc.- 579.5 nm λdet. - 1.044 nm
τ300K (L)=1.0ms I/I 0
τ77K (M)=115μs τ77K (L)=1.0ms 0.1
τ300K (M)=17.5μs 0.0
0.2
0.4
0.6
References [1] T.T. Basiev, V.B. Sigachev, M.E. Doroshenko, A.G. Papashvili, V.V. Osiko, Spectroscopic and laser properties of Nd3+ doped fluoride crystals in 1.3 lm region, Proc. SPIE (USA) 2498 (1995) 14. [2] P.P. Fedorov, V.V. Osiko, T.T. Basiev, Yu.V. Orlovskii, K.V. Dukel’skii, I.A. Mironov, V.A. Demidenko, A.N. Smirnov, Optical fluoride nanoceramics, Russ. Nanotechnol. 2 (5–6) (2007) 95–105. [3] T.T. Basiev, M.E. Doroshenko, P.P. Fedorov, V.A. Konyushkin, S.V. Kuznetsov, V.V. Osiko, M.Sh. Akchurin, Efficient laser based on CaF2–SrF2–YbF3 nanoceramics, Opt. Lett. 33 (5) (2008) 521–523. [4] Yu.V. Orlovskii, T.T. Basiev, I.N. Vorob’ev, V.V. Osiko, A.G. Papashvili, A.M. Prokhorov, Site – selective measurements of 4G5/2; 2G7/2 nonradiative relaxation rate in Nd:SrF2, Nd:La:SrF2, and Nd:Sr:LaF3 laser crystals, Laser Phys. 6 (3) (1996) 448–455.
λexc.=579.5 nm
SrF2 :Nd 3+
This work is supported by the US Civilian Research and Development Foundation (Grant #RUP2-1517-MO-06) and Russian Fund for Basic Research (Project #08-02-01221a).
0.8
Time, ms Fig. 11. Decay curves of Nd3+ ions at 4F3/2–4I9/2 at room temperature and 77 K.
Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Investigation of Nd3+ ions spectroscopic and laser properties in SrF2 fluoride single crystal O.K. Alimov, T.T. Basiev, M.E. Doroshenko ⇑, P.P. Fedorov, V.A. Konyushkin, A.N. Nakladov, V.V. Osiko Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow, Russia
a r t i c l e
i n f o
Article history: Received 30 March 2011 Received in revised form 2 November 2011 Accepted 8 November 2011 Available online 26 December 2011 Keywords: Rare-earth doped fluoride Diode laser pumping Optical centers spectroscopy
a b s t r a c t The laser properties of SrF2:Nd3+ crystal with neodymium ions concentration of 0.5 at.% were investigated under diode laser pumping. Using temperature tuning of laser diode pumping wavelength two different lines centered at about 1037 nm and 1044 nm attributed to oscillation of different optical centers were obtained. The maximum lasing slope efficiency of 37% was obtained. The absorption and fluorescence spectra of different individual and clustered Nd3+ ions optical centers were observed depending on Nd3+ concentration. The lifetimes of the high symmetry L-centers were measured and found to be two orders of magnitude longer than that for clustered M-centers at room temperature. The lifetimes of M-centers at different temperatures were measured and microparameter of ion–ion interaction in Nd-pairs was determined. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Neodymium doped fluoride crystals attracts growing attention for development of diode-pumped lasers due to specific spectroscopic properties of Nd3+ ions including rather broad absorption and fluorescence spectra together with long radiative lifetime of 4 F3/2 state. Trivalent rare-earth ions in fluorides are known to form different optical centers due to heterovalent substitution of divalent cations and different forms of charge compensation. The set of optical centers usually depends on the type of rare-earth ions, their concentration and fluoride host. Existence of wide range of fluoride solid-solutions also allows to influence the process of optical centers formation and thus manipulate the spectroscopic and oscillation properties of rare-earth ions [1]. Additional advantage of these materials that they could be obtained in the form of high optical quality laser ceramics [2,3]. 2. Experimental setup To investigate the laser properties of neodymium-doped single crystals a setup based on a PUMA laser diode with the maximum average output power of 15 W was used. The laser diode was fiber coupled with the fiber core diameter of 120 lm. The pump radiation was focused inside the active crystal by single spherical lens. The output energy was measured using EPM-2000 energy meter. The oscillation spectra were measured by LRL-005 wavelength meter. ⇑ Corresponding author. Tel.: +7 499 1350318; fax: +7 499 1350270. E-mail address: [email protected] (M.E. Doroshenko). 0925-3467/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2011.11.010
For spectroscopic measurements pulsed tunable Ti:sapphire and dye lasers pumped by second harmonics of Q-switched YAG:Nd laser were applied. 3. Laser properties of SrF2:Nd3+ crystal under LD pumping The oscillation properties of the crystals were studied using the cavity formed by a flat dichroic mirror which was deposited to one side of the crystal with antireflection coating on the other and a curved output mirror with 50-mm curvature placed at about 35 mm distance from the flat dichroic mirror. The reflectivity of the output mirror was changed to optimize the laser output. In Fig. 1, the input–output characteristics of the laser based on SrF2:Nd3+ crystal is demonstrated. The length of the SrF2:Nd3+ crystal used was 10 mm so the lens with the focal length of 12 mm was used to form the pump waist inside the crystal. To optimize the pump profile the distance from the lens to the fiber end was optimized to be about 1.8 of the lens focal length. As can be seen from the figure the slope efficiency of 27% was obtained in case of 95% reflectivity of the output mirror. To optimize the output different focusing lenses were tested. In Fig. 2, the input–output characteristics of SrF2:Nd3+ crystal are shown for different focal lengths of the focusing lens. As could be seen from the figure maximum output was realized for lens with focal length of 8 mm where slope efficiency of 29% was demonstrated. For each case the distance from the lens to the fiber end was optimized to obtain the most effective matching between the pump and cavity oscillating mode. Measurements of the oscillation spectrum showed that in case of 789 nm pumping and output mirror reflectivity of 95% for low
800
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
1.5
Output Power, W
1.0
Output Power, W
1.5
SrF2 :Nd 3+
R=95% η sl =27%
τ pump =3 ms, f=10Hz f=12 mm
R=85% η sl =13%
3+
SrF2 :Nd 1.0
f=10Hz; τ pump =3 ms
0.5
R=95% λ exc =789nm
0.0 0.0
0.5
1.5
3.0
4.5
6.0
Absorbed Power, W 0.8 0.0 0.0
1.5
3.0
4.5
0.4
6.0
Absorbed Power, W
0.0
Fig. 1. Input–output characteristics of SrF2:Nd3+ crystal for different reflectivities of the output mirror.
0.8
pumping level oscillations occur only at the wavelength of 1037 nm. For higher pumping levels additional oscillating line centered at about 1044 nm appears as can be seen in Fig. 3. For output mirror reflectivity of 85% oscillations only at 1037 nm line were observed. The oscillation spectrum of SrF2:Nd3+ crystal was also found to depend on the laser diode (LD) pumping wavelength. In Fig. 4, the laser diode oscillation spectra temperature tuning with respect to absorption spectra of SrF2:Nd3+ crystal is demonstrated. The shift of the pumping wavelength from 789 nm to 793 nm (two local maxima at the SrF2:Nd3+ absorption spectrum) resulted in the strong change between the two oscillating lines intensity distribution as can be seen in Fig. 4. The plot of the normalized oscillating line intensities versus the laser diode pumping wavelength (for maximum pumping level) is shown in Fig. 5. As can be seen from the figure the shift of pumping wavelength from 789 nm to 793 nm results in completely inverse ratio in the oscillating lines intensities. Input–output characteristics on SrF2:Nd3+ crystal pumped in absorption maximum of 796 nm is shown in Fig. 6 where slope efficiency as high as 37% was achieved. For this pumping wavelength the intensity of both oscillating lines (1037 nm and 1044 nm) was practically equal. 4. Spectroscopic properties investigation Fluorides of SrF2 type doped with trivalent rare-earth ions are known to form different optical centers due to several possibilities
1.5
Output Power, W
SrF2:Nd
1.0
3+
R=95% f=10Hz, τ pump =3ms
f=8 mm η sl =29% f=12 mm ηsl =27%
0.5
f=65 mm ηsl =11% 0.0 0.0
1.5
3.0
4.5
6.0
Absorbed Power, W Fig. 2. Input–output characteristics of SrF2:Nd3+ crystal for different focal lengths of the lens.
Intensity
0.4 0.0 0.8 0.4 0.0 0.8 0.4 0.0 1036
1038
1040
1042
1044
Wavelength, nm Fig. 3. Oscillation spectrum of SrF2:Nd3+ crystal for different pumping levels.
of excessive charge compensation. With increased concentration of rare-earth ions also different clusters are formed. These different types of optical centers are characterized by different spectroscopic properties. The room temperature fluorescence spectrum of SrF2:Nd3+ crystal is characterized by two maxima at 1037 nm and 1044 nm. To investigate the contribution of different optical centers to the fluorescence spectrum and maxima the time resolved fluorescence spectra of SrF2:Nd3+ crystal were measured shown in Fig. 7. In this experiment pulsed tunable titanium sapphire laser pumped with nanosecond second harmonic YAG:Nd pulses was used as excitation source. As could be seen from the figure fluorescence spectra for long lifetime and short lifetime selection are different which corresponds to fluorescence of highsymmetry tetragonal L-centers and paired rhombic M-centers respectively. To determine the contribution of different optical centers to different oscillation lines the decay curves were measured for the excitation wavelengths of 789 nm and 793 nm. The measured decay curves are presented in Fig. 8. As could be seen from the figure for 789 nm excitation contribution of high symmetry tetragonal optical centers with long lifetime of about 1.0 ms to fluorescence at 1037 nm prevails. For 793 nm excitation the contribution of M-clustered centers with short lifetime of about 17.5 ls is sufficiently increased especially for 1044 nm fluorescence in accordance with the obtained fluorescence spectrum of clustered centers. As also follows from Fig. 9 the decay curve in SrF2:Nd3+ crystal could be described by two exponents which corresponds to two types of optical centers with lifetimes of 1 ms for high symmetry tetragonal optical L-centers and 17.5 ls for clustered M-centers.
801
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
5
1.5
Laser Diode spectrum
3+
SrF2 :Nd
0.5
0.0 780
785
790
795
800
805
f=12 mm 3
R=95% λex =796 nm
2
ηsl =37%
1
Wavelength, nm
0
λ pump =789 nm Intensity
3+
τ pump =3 ms, f=10Hz
4
1.0
Output Power, W
Absorption
SrF2 :Nd
0
2
4
0.8
6
8
10
12
Absorbed Power, W Fig. 6. Input–output characteristics of SrF2:Nd3+ crystal pumped in absorption maximum.
0.4
0.0
0.8
1038
1040
1042
1044
1046
λ pump =793 nm
SrF2 :Nd 3+
0.4
L-centers 0.0 1036
1038
1040
1042
1044
1046
Wavelength, nm
Intensity
Intensity
1036
M-centers
Fig. 4. Dependence of the SrF2:Nd3+ crystal oscillation spectrum on pumping wavelength.
1000
1020
1040
1080
110 0
λ osc =1037nm
Fig. 7. Time resolved fluorescence spectrum of Nd3+ in SrF2 crystal.
0.8 0.6
1
0.4
SrF 2:Nd
λ osc =1044nm 0.2 0.0 788
3+
Mostly L-centers λex=789 nm
0.6
λreg=1037 nm
0.4 790
792
794
796
798
LD Pumping Wavelength, nm
I/Io
Normalized Intensity
1060
Wevelength, nm
1.0
Fig. 5. Normalized relation between oscillation lines intensities for different pumping wavelengths.
0.2
The spectroscopic properties of Nd3+ ions optical centers in SrF2 crystal were also investigated using excitation with Rodamin 6G 2 tunable dye laser via excitation of 4I9/2– G7/2; 4G5/2 transition. As follows from [4] the absorption lines of clustered Nd3+ M-centers 2 could be separated in absorption spectrum at 4I9/2– G7/2; 4G5/2 transition especially at liquid nitrogen temperature. The absorption spectrum at 300 K and 77 K temperature is shown in Fig. 10 with the M-centers absorption line marked with an arrow. For both cases the decay curve was double exponential. For room temperature the short component lifetime was measured to be 17.5 ls while long one the lifetime was 1 ms which is the same value as was obtained for M-centers and L-centers above
0.1 0.0
M+L - centers λex=793 nm λreg=1044 nm 0.5
1.0
1.5
2.0
Time, ms Fig. 8. Decay curves of Nd3+ ions in SrF2 for different excitation and registration wavelengths.
for Ti:sapphire excitation. For liquid nitrogen temperature the short decay component demonstrates increase both in relative (to long component) intensity and duration. The measured decay time for short component increased from 17.5 ls to 115 ls while decay time for long component stayed unchanged (see Fig. 11).
802
O.K. Alimov et al. / Optical Materials 34 (2012) 799–802
1.0
SrF2 :Nd
0.8
5. Conclusions
3+
Different Nd3+ optical centers in SrF2 crystal were determined and their absorption and fluorescence spectra and lifetimes were measured. Oscillation spectrum of Nd3+ ions in SrF2 crystal was found to change with laser diode pumping wavelength depending on excitation of different Nd3+ optical centers. Laser oscillations of Nd3+ ions in SrF2 crystal under laser diode pumping were obtained with slope efficiency up to 37%.
I/Io
0.4
τ 2=1 ms 0.2
τ 1 =17.5 μs
Acknowledgments
0.1 0
20
40
60
80
100
120
140
160
Time, μs Fig. 9. Double exponential decay curve of Nd3+ ions in SrF2 crystal for high symmetry L-centers and clustered M-centers.
9/2
--> 2 G
7/2
;4 G
M-centers
5/2
Absorption
4I
T=300K
T=77K
560
570
580
590
Wavelength, nm Fig. 10. Absorption spectra of Nd3+ ions at 4I9/2–2G7/2; 2G5/2 transition at 300 K and 77 K.
1
3+
SrF2:0.5%Nd
λexc.- 579.5 nm λdet. - 1.044 nm
τ300K (L)=1.0ms I/I 0
τ77K (M)=115μs τ77K (L)=1.0ms 0.1
τ300K (M)=17.5μs 0.0
0.2
0.4
0.6
References [1] T.T. Basiev, V.B. Sigachev, M.E. Doroshenko, A.G. Papashvili, V.V. Osiko, Spectroscopic and laser properties of Nd3+ doped fluoride crystals in 1.3 lm region, Proc. SPIE (USA) 2498 (1995) 14. [2] P.P. Fedorov, V.V. Osiko, T.T. Basiev, Yu.V. Orlovskii, K.V. Dukel’skii, I.A. Mironov, V.A. Demidenko, A.N. Smirnov, Optical fluoride nanoceramics, Russ. Nanotechnol. 2 (5–6) (2007) 95–105. [3] T.T. Basiev, M.E. Doroshenko, P.P. Fedorov, V.A. Konyushkin, S.V. Kuznetsov, V.V. Osiko, M.Sh. Akchurin, Efficient laser based on CaF2–SrF2–YbF3 nanoceramics, Opt. Lett. 33 (5) (2008) 521–523. [4] Yu.V. Orlovskii, T.T. Basiev, I.N. Vorob’ev, V.V. Osiko, A.G. Papashvili, A.M. Prokhorov, Site – selective measurements of 4G5/2; 2G7/2 nonradiative relaxation rate in Nd:SrF2, Nd:La:SrF2, and Nd:Sr:LaF3 laser crystals, Laser Phys. 6 (3) (1996) 448–455.
λexc.=579.5 nm
SrF2 :Nd 3+
This work is supported by the US Civilian Research and Development Foundation (Grant #RUP2-1517-MO-06) and Russian Fund for Basic Research (Project #08-02-01221a).
0.8
Time, ms Fig. 11. Decay curves of Nd3+ ions at 4F3/2–4I9/2 at room temperature and 77 K.