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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 21 — Oct. 8, 2012
  • pp: 23690–23699
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Laser action in Nd3+-doped lanthanum oxysulfide powders

Iñaki Iparraguirre, Jon Azkargorta, Odile Merdrignac-Conanec, Mohamad Al-Saleh, Christophe Chlique, Xianghua Zhang, Rolindes Balda, and Joaquín Fernández  »View Author Affiliations


Optics Express, Vol. 20, Issue 21, pp. 23690-23699 (2012)
http://dx.doi.org/10.1364/OE.20.023690


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Abstract

We have investigated the stimulated emission properties of Nd3+ doped La2O2S powders at room temperature as a function of pumping energy density, excitation wavelength, and Nd3+ ion concentration. The absolute stimulated emission energy has been measured. Expressions for the slope efficiencies and lasing thresholds as a function of rare earth concentration and pumping wavelengths, which qualitatively agree with experimental observations, are discussed.

© 2012 OSA

1. Introduction

Among the RE-doped oxides, oxysulfides (RE2O2S) are one of the most efficient phosphors investigated for commercial television and lighting applications [1

1. W. M. Yen, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed. (CRC Press, 2007).

]. In particular, lanthanum oxysulfide crystal matrix, a uniaxial P3¯mwide-gap (36000 cm−1) [14

14. C. W. Struck and W. H. Fonger, “Dissociation of Eu3+ Charge-Transfer in Y2O2S and La2O2S into Eu2+ and a Free Hole,” Phys. Rev. B 4(1), 22–34 (1971). [CrossRef]

] semiconductor material, is known as an excellent host lattice for trivalent RE ions [15

15. R. V. Alves, R. A. Buchanan, K. A. Wickersheim, and E. A. C. Yates, “Neodymium-activated Lanthanum Oxysulfide: A new high-gain laser material,” J. Appl. Phys. 42(8), 3043–3048 (1971). [CrossRef]

]. Each lanthanum atom is coordinated by four oxygen atoms and three sulfur atoms in its nearest neighborhood [16

16. G. I. Abutalibov, D. I. Guseynov, and A. A. Mamedov, “Nd3+-ion luminescence in La2O2S and Y2O2S single crystals,” Phys. Status Solidi., C Curr. Top. Solid State Phys. 6(5), 1127–1129 (2009). [CrossRef]

]. The lanthanum site symmetry is C3v. The spectroscopic and laser properties of Nd3+-activated lanthanum oxysulfide crystal has been worked out by Alves and associates in [15

15. R. V. Alves, R. A. Buchanan, K. A. Wickersheim, and E. A. C. Yates, “Neodymium-activated Lanthanum Oxysulfide: A new high-gain laser material,” J. Appl. Phys. 42(8), 3043–3048 (1971). [CrossRef]

], and twenty years later, Markushev and associates shortly presented preliminary results obtained at liquid nitrogen temperature on the stimulated emission kinetics of a La2O2S powder doped with 1% of Neodymium [17

17. V. M. Markushev, N. E. Ter-Gabrelyan, Ch. M. Briskina, V. R. Belan, and V. F. Zolin, “Stimulated emission kinetics of neodymium powder lasers,” Sov. J. Quantum Electron. 20(7), 773–777 (1990). [CrossRef]

].

In this work, to our knowledge, lasing action from Nd3+ doped La2O2S powders at room temperature is presented for the first time. We have investigated the stimulated emission properties of this material as a function of pumping energy density, wavelength, and Nd3+ ion concentration and measured the absolute stimulated emission energy by assuming Lambertian emission. The most relevant results have been compared with those found in the stoichiometric borate NdAl(BO3)4, which is one of the most investigated random laser materials [6

6. M. A. Noginov, “Solid-State Random Lasers,” (Springer, Berlin, 2005).

, 13

13. J. Azkargorta, M. Bettinelli, I. Iparraguirre, S. García-Revilla, R. Balda, and J. Fernández, “Random lasing in Nd:LuVO4 crystal powder,” Opt. Express 19(20), 19591–19599 (2011). [CrossRef] [PubMed]

, 18

18. S. García-Revilla, I. Iparraguirre, C. Cascales, J. Azkargorta, R. Balda, M. A. Illarramendi, M. Al Saleh, and J. Fernández, “Random laser performance of NdxY1-xAl3(BO3)4 laser crystal powders,” Opt. Mater. 34(2), 461–464 (2011). [CrossRef]

].

2. Slope and threshold measurements

2.1. Experimental conditions

The pumping source was a tunable 10 ns time width Ti:sapphire pulsed laser. The pump beam size over the sample surface was controlled by means of a 60 cm focal lens mounted in a movable holder. The emission was directly collected (without lens) on a 0.5 mm diameter optic fiber, vertically located at a distance of 12 cm over the sample; therefore, though the emission energy is given in arbitrary units all measurements for different pump beam sizes, concentrations or wavelengths may be compared with each other. The fiber drives the optical signal to a fast detector directly coupled to a 1 Ghz bandwidth digital oscilloscope. To remove the pump signal and to avoid measurement saturation, a long wave pass filter and neutral attenuation filters were intercalated. As it is well known, when the pumping energy is higher than the threshold one, the temporal length of the emitted pulse shortens from tens of microseconds corresponding to the spontaneous emission time, down to the nanosecond domain. Thus, in order to collect the stimulated emission the recording time basis was set to the nanosecond scale, because the narrowed emission is dominant when the material is lasing, and the residual spontaneous contribution is negligible.

The pumping energy was calibrated by comparing the measurement given by an optical head detector, Ophir PE25BF-V2 ROHS, located at the exact position where powder samples were pumped, and the one provided by a silicon detector which measures the light dispersed by the folder mirror used to address the pump beam. Thus it is possible to measure pumping and output pulse energies simultaneously.

The procedure to measure the pump beam size over the sample consisted in collecting the diffused pump radiation on the sample surface with a CCD camera (Newport LBP-3-USB) by means of a carefully focused imaging lens and filtering the sample emission at 1 μm. With the aim of verifying the accuracy of the measured beam sizes at different focalizations and to avoid the possible distorting effect of the diffusion of pump radiation in the sample, we have used polished metal samples, with the same setup configuration, and the obtained results were similar.

The measurements were carried out with 2, 3, 6, and 9 mol % Nd3+-doped samples of La2O2S, using different pump beam sizes. The optimal pumping wavelength was found to be 819 nm. The spectrum of the laser emission was centered at 1076 nm and its width was about 0.2 nm, which is the spectral resolution limit of our system.

2.2 Experimental results

Figure 1(a)
Fig. 1 (a) Output energy in arbitrary units as a function of incident pump energy for different Nd3+ concentrations, obtained with a 3.22 mm2 pump beam area. (b) Output energy in arbitrary units as a function of incident pump energy for different pump beam areas, obtained from the 9 mol% of Nd3+-doped sample.
displays the output energy as a function of incident pump energy for the different Nd3+ concentrations. As can be seen, the pump threshold energy for stimulated emission slightly decreases as a function of concentration, whereas the slope efficiency clearly rises with it. The output energy as a function of the incident pump energy for some different pump areas is shown in Fig. 1(b), where, as in Fig. 1(a), the maximum pump energy at different pump areas is limited by the damage threshold of the powders, about 10 mJ/mm2. As can be seen, the slope efficiency remains essentially constant whereas the threshold energy for stimulated emission is reduced as the pump area decreases. We have observed that this reduction is proportional to the pumping beam area, so the pumping threshold energy per unit area remains constant in the working range of Fig. 1(b).

With the aim of finding the limit to this behavior, we have reduced the pumping area down to sizes of 200 μm in diameter. Figure 2
Fig. 2 Threshold energy for stimulated emission (black dots in right-side ordinate axis) and threshold energy per area unit (red dots in left-side ordinate axis), as a function of pump beam area, for 9 mol% Nd3+ doped sample. Straight lines are linear fits to experimental points.
shows the pump threshold energy (black dots) and pump threshold energy per unit area (red dots) as a function of the pumped area. As can be seen, the pump threshold energy is approximately linear whereas the threshold energy per unit area fits well to a horizontal line for beam areas above 0.5 mm2 (diameters above 0.8 mm). The conclusion is that the pump threshold energy per unit area remains constant for diameters above 0.8 mm. We have also done the same kind of measurements with NdAl3(BO3)4 stoichiometric sample, obtaining very similar results, which significantly differ from previously reported ones [18

18. S. García-Revilla, I. Iparraguirre, C. Cascales, J. Azkargorta, R. Balda, M. A. Illarramendi, M. Al Saleh, and J. Fernández, “Random laser performance of NdxY1-xAl3(BO3)4 laser crystal powders,” Opt. Mater. 34(2), 461–464 (2011). [CrossRef]

, 20

20. M. Bahoura, K. J. Morris, G. Zhu, and M. A. Noginov, “Dependence of the Neodymium random laser threshold on the diameter of the pumped spot,” IEEE J. Quantum Electron. 41(5), 677–685 (2005). [CrossRef]

, 21

21. M. Bahoura, K. J. Morris, and M. A. Noginov, “Threshold and slope efficiency of Nd0.5La0.5Al3(BO3)4 ceramic random laser: effect of the pumped spot size,” Opt. Commun. 201(4-6), 405–411 (2002). [CrossRef]

] by other authors and show the importance of a careful measurement of the pump beam size. The average grain size of all samples used (about one micron) is large enough to have no significant influence on the laser threshold [6

6. M. A. Noginov, “Solid-State Random Lasers,” (Springer, Berlin, 2005).

].

3. Absolute energy measurements

The conclusions obtained from the experimental results can be summarized as follows:

  • -The slope efficiency remains essentially constant with respect to changes in the pump beam size (above 0.8 mm in diameter) and tends to grow when concentration is increased.
  • -The incident pump threshold energy per unit area also remains constant as a function of the pump beam size for diameters larger than 0.8 mm. However, though one would predict noticeable changes in the behavior of this magnitude as a function of concentration and wavelength, these were not so significant as expected.

4. Discussion

4.1 Slope efficiencies

In order to explain the obtained results, we have compared the absolute slope efficiencies experimentally obtained with the corresponding absorbance of the powders for different concentrations and pumping wavelengths. The results which can be seen in Table 1

Table 1. Absorbance values and calculated (by using Eq. (1)) and experimental slope efficiencies in Nd3+-doped oxysulfides. We take as normalized absorbance the difference between the diffuse reflectance in the flat no absorbing zone (780-790 nm) and the one at the corresponding wavelength.

table-icon
View This Table
conclude that slope efficiencies are essentially given by the absorbance of powder multiplied by the ratio between the emission and pumping photon energies; in other words, all the absorbed pumping photons above threshold are mainly reemitted as stimulated emission. This would be extensible only to powder materials with spontaneous decay times much longer than pumping time, and with not too small pump beam sizes which would give different laser dynamics. Therefore, the following formula is applicable:
m=ηνemνp
(1)
where m is the absolute slope efficiency of the stimulated emission energy versus the incident pump energy, η is the absorbance of powder at the pumping wavelength, calculated from Fig. 5 and given in Table 1, and νp and νem the photon frequencies corresponding to the pumping and stimulated emission radiation respectively.

As can be seen in Table 1, the predicted values of slope efficiencies fit m experimental values quite well. It is worth noticing that the experimental slope efficiency is always slightly lower than the one calculated from absorbance, which surely indicates spurious losses in stimulated emission.

4.2 Lasing threshold

In a simple diffusion model, the theory of random lasers shows that, in a first approximation, assuming slab geometry and pump beam sizes much larger than the absorption length, the laser threshold is reached at a critical thickness of pumped volume [27

27. D. S. Wiersma and A. Lagendijk, “Light diffusion with gain and random lasers,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 54(4), 4256–4265 (1996). [CrossRef] [PubMed]

]:
lcr=πltlg3
(2)
being lt the transport length and lg the gain length. Taking into account that the depth of the pumped zone is essentially the diffusive absorption length labs, which is given by:
labs=ltli3
(3)
being li the inelastic length, the laser threshold is reached when Eqs. (2) and (3) are equal, so the condition li = π 2lg is accomplished, where
li=1σabsρ,lg=1σemNth
being σabs the absorption cross-section at pumping wavelength, ρ the concentration in ions per unit volume, σem the stimulated emission cross-section and Nth the threshold population inversion in particles per unit volume. Then, the value for the threshold population inversion is:

Nth=π2σabsρσem
(4)

By the other hand, the population inversion N can be written as a function of the absorbed energy as:
N=EabshνpAlabs
(5)
where Eabs is the absorbed energy, given by the pumping incident energy multiplied by the absorbance η, h is the Planck constant, and A is the pumping area. Equating Eqs. (4) and (5), we obtain the incident threshold pumping energy by:
Eth(incident)=1η×π2hνpA3×ltσem×σabsρ
(6)
(a similar result can be found in [6

6. M. A. Noginov, “Solid-State Random Lasers,” (Springer, Berlin, 2005).

]). In our case, the relevant parameters are the concentration ρ, the absorption cross-section σabs, which depends on the pumping wavelength, and the absorbance η, depending both on pumping wavelength and concentration. In this way, Eq. (6) can be written as:

Eth(incident)σabsρη
(7)

If we compare results obtained from the last Eq. (7) with our experimental results, the very slight changes of threshold pumping energy with concentration can be qualitatively explained. When concentration is increased, absorbance also grows finally resulting in very little changes in the threshold energy. The quantitative accordance between our experimental results and those predicted by this formula when concentration is changed is nevertheless rather rough.

However, changes of the threshold pumping energy as a function of pumping wavelength are satisfactorily compared. For example, the experimentally obtained threshold energies for the 9% doped sample using a pump beam area of 4.80 mm2, at pumping wavelengths of 819 nm and 808 nm are 9 mJ and 15 mJ respectively, (see Fig. 3), being 0.6 its ratio. If we do calculations from Eq. (7), by using the absorbance from Table 1, and the absorption cross-section corresponding to these wavelengths [15

15. R. V. Alves, R. A. Buchanan, K. A. Wickersheim, and E. A. C. Yates, “Neodymium-activated Lanthanum Oxysulfide: A new high-gain laser material,” J. Appl. Phys. 42(8), 3043–3048 (1971). [CrossRef]

], we obtain the same value, with an error less than 5%, which is a is a very good agreement, and is confirmed by our tests in stoichiometric borate.

As a conclusion we propose Eq. (1) for the calculation of absolute slope efficiency and Eqs. (6)-(7) for the evaluation of the pumping threshold energy of a Nd3+ random laser (pumped by using beam sizes higher than 0.8 mm in diameter). The validity limit of these expressions can change as a function of material, but account taken of the good agreement among the different samples studied, including the stoichiometric borate, we would anticipate it might be quite general.

5. Conclusions

We have investigated the stimulated emission properties of Nd3+ doped La2O2S powders at room temperature as a function of pumping energy density, excitation wavelength, and Nd3+ ion concentration. The absolute stimulated emission energy of the doped powders has been measured. The maximum value of the slope efficiency, referred to the pump energy is larger than 15% being 2.5 mJ the maximum emitted energy. These values closely compare to the ones measured for the stoichiometric borate which are 35% and 6 mJ respectively.

The experimental results demonstrate that the slope efficiency remains essentially constant with respect to changes in the pump beam size (above 0.8 mm in diameter) and tends to grow when concentration is increased. Moreover, the incident pump threshold energy per unit area also remains constant as a function of the pump beam size for diameters larger than 0.8 mm.

We have obtained approximate expressions for the slope efficiencies and lasing thresholds as a function of rare earth concentration and pumping wavelengths. Though changes in threshold pumping energy with concentration can be only qualitatively explained, changes in threshold pumping energy as a function of pumping wavelength and slope efficiencies are satisfactorily compared.

Acknowledgments

This work was supported by the Spanish Government under projects FIS2011-27968 and Consolider CSD2007-00013 (SAUUL) and by the Basque Country Government (IT-331-07).

References and links

1.

W. M. Yen, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed. (CRC Press, 2007).

2.

G. A. Kumar, J. Lu, A. A. Kaminskii, K. I. Ueda, H. Yagi, and T. Yanagitani, “Spectroscopic and stimulated emission characteristics of Nd3+ in transparent Y2O3 ceramics,” IEEE J. Quantum Electron. 42, 643–650 (2006) (and references therein). [CrossRef]

3.

Yu. V. Orlovskii, T. T. Basiev, K. K. Pukhov, M. V. Polyachencova, P. P. Fedorov, O. K. Alimov, E. I. Gorokhova, V. A. Demidenko, O. A. Khristich, and R. M. Zakalyukin, “Oxysulfide optical ceramics doped by Nd3+ for one micron lasing,” J. Lumin. 125(1-2), 201–215 (2007). [CrossRef]

4.

D. S. Wiersma, “The physics and applications of random lasers,” Nat. Phys. 4(5), 359–367 (2008). [CrossRef]

5.

B. Redding, M. A. Choma, and H. Cao, “Speckle-free laser imaging using random laser illumination,” Nat. Photonics 6(6), 355–359 (2012). [CrossRef]

6.

M. A. Noginov, “Solid-State Random Lasers,” (Springer, Berlin, 2005).

7.

H. Cao, “Lasing in random media,” Waves Random Media 13(3), R1–R39 (2003). [CrossRef]

8.

D. S. Wiersma and M. A. Noginov, “Nano and random lasers,” J. Opt. 12(2), 020201–024014 (2010). [CrossRef]

9.

J. Andreasen, A. A. Asatryan, L. C. Botten, M. A. Byrne, H. Cao, L. Ge, L. Labonté, P. Sebbah, A. D. Stone, H. E. Türeci, and C. Vanneste, “Modes of random lasers,” Adv. Opt. Photon. 3(1), 88–127 (2011). [CrossRef]

10.

M. A. Noginov, N. E. Noginova, H. J. Caulfield, P. Venkateswarlu, T. Thompson, M. Mahdi, and V. Ostroumov, “Short-pulsed stimulated emission in the powders of NdAl3(BO3)4, NdSc3(BO3)4 and Nd:Sr5(PO4)3F laser crystals,” J. Opt. Soc. Am. B 13(9), 2024–2033 (1996). [CrossRef]

11.

C. Gouedard, D. Husson, C. Sauteret, F. Auzel, and A. Migus, “Generation of spatially incoherent short pulses in laser-pumped neodymium stoichiometric crystals and powders,” J. Opt. Soc. Am. B 10(12), 2358–2363 (1993). [CrossRef]

12.

G. Zhu, T. Tumkur, and M. A. Noginov, “Anomalously delayed stimulated emission in random lasers,” Phys. Rev. A 81(6), 065801 (2010). [CrossRef]

13.

J. Azkargorta, M. Bettinelli, I. Iparraguirre, S. García-Revilla, R. Balda, and J. Fernández, “Random lasing in Nd:LuVO4 crystal powder,” Opt. Express 19(20), 19591–19599 (2011). [CrossRef] [PubMed]

14.

C. W. Struck and W. H. Fonger, “Dissociation of Eu3+ Charge-Transfer in Y2O2S and La2O2S into Eu2+ and a Free Hole,” Phys. Rev. B 4(1), 22–34 (1971). [CrossRef]

15.

R. V. Alves, R. A. Buchanan, K. A. Wickersheim, and E. A. C. Yates, “Neodymium-activated Lanthanum Oxysulfide: A new high-gain laser material,” J. Appl. Phys. 42(8), 3043–3048 (1971). [CrossRef]

16.

G. I. Abutalibov, D. I. Guseynov, and A. A. Mamedov, “Nd3+-ion luminescence in La2O2S and Y2O2S single crystals,” Phys. Status Solidi., C Curr. Top. Solid State Phys. 6(5), 1127–1129 (2009). [CrossRef]

17.

V. M. Markushev, N. E. Ter-Gabrelyan, Ch. M. Briskina, V. R. Belan, and V. F. Zolin, “Stimulated emission kinetics of neodymium powder lasers,” Sov. J. Quantum Electron. 20(7), 773–777 (1990). [CrossRef]

18.

S. García-Revilla, I. Iparraguirre, C. Cascales, J. Azkargorta, R. Balda, M. A. Illarramendi, M. Al Saleh, and J. Fernández, “Random laser performance of NdxY1-xAl3(BO3)4 laser crystal powders,” Opt. Mater. 34(2), 461–464 (2011). [CrossRef]

19.

B. Fan, C. Chlique, O. Merdrignac-Conanec, X. Zhang, and X. Fan, “Near-Infrared quantum cutting material Er3+/Yb3+ doped La2O2S with an external quantum yield higher than 100%,” J. Phys. Chem. C 116(21), 11652–11657 (2012). [CrossRef]

20.

M. Bahoura, K. J. Morris, G. Zhu, and M. A. Noginov, “Dependence of the Neodymium random laser threshold on the diameter of the pumped spot,” IEEE J. Quantum Electron. 41(5), 677–685 (2005). [CrossRef]

21.

M. Bahoura, K. J. Morris, and M. A. Noginov, “Threshold and slope efficiency of Nd0.5La0.5Al3(BO3)4 ceramic random laser: effect of the pumped spot size,” Opt. Commun. 201(4-6), 405–411 (2002). [CrossRef]

22.

M. A. Noginov, M. Bahoura, N. Noginova, and V. P. Drachev, “Study of absorption and reflection in solid-state random laser media,” Appl. Opt. 43(21), 4237–4243 (2004). [CrossRef] [PubMed]

23.

M. A. Illarramendi, I. Aramburu, J. Fernández, R. Balda, S. N. Williams, J. A. Adegoke, and M. A. Noginov, “Characterization of light scattering in translucent ceramics,” J. Opt. Soc. Am. B 24(1), 443–448 (2007). [CrossRef]

24.

M. A. Noginov, N. E. Noginova, S. U. Egarievwe, H. J. Caulfield, P. Venkateswarlu, A. Williams, and S. B. Mirov, “Color-center powder laser: The effect of pulverization on color-center characteristics,” J. Opt. Soc. Am. B 14(8), 2153–2160 (1997). [CrossRef]

25.

M. A. Noginov, S. U. Egarievwe, N. Noginova, H. J. Caulfield, and J. C. Wang, “Interferometric studies of coherence in a powder laser,” Opt. Mater. 12(1), 127–134 (1999). [CrossRef]

26.

V. M. Markushev, V. F. Zolin, and C. M. Briskina, “Luminescence and stimulated emission of neodymium in sodium lanthanum molybdate powders,” Sov. J. Quantum Electron. 16(2), 281–283 (1986). [CrossRef]

27.

D. S. Wiersma and A. Lagendijk, “Light diffusion with gain and random lasers,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 54(4), 4256–4265 (1996). [CrossRef] [PubMed]

OCIS Codes
(140.3530) Lasers and laser optics : Lasers, neodymium
(160.5690) Materials : Rare-earth-doped materials

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 25, 2012
Revised Manuscript: September 13, 2012
Manuscript Accepted: September 13, 2012
Published: October 1, 2012

Citation
Iñaki Iparraguirre, Jon Azkargorta, Odile Merdrignac-Conanec, Mohamad Al-Saleh, Christophe Chlique, Xianghua Zhang, Rolindes Balda, and Joaquín Fernández, "Laser action in Nd3+-doped lanthanum oxysulfide powders," Opt. Express 20, 23690-23699 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-21-23690


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References

  1. W. M. Yen, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed. (CRC Press, 2007).
  2. G. A. Kumar, J. Lu, A. A. Kaminskii, K. I. Ueda, H. Yagi, and T. Yanagitani, “Spectroscopic and stimulated emission characteristics of Nd3+ in transparent Y2O3 ceramics,” IEEE J. Quantum Electron.42, 643–650 (2006) (and references therein). [CrossRef]
  3. Yu. V. Orlovskii, T. T. Basiev, K. K. Pukhov, M. V. Polyachencova, P. P. Fedorov, O. K. Alimov, E. I. Gorokhova, V. A. Demidenko, O. A. Khristich, and R. M. Zakalyukin, “Oxysulfide optical ceramics doped by Nd3+ for one micron lasing,” J. Lumin.125(1-2), 201–215 (2007). [CrossRef]
  4. D. S. Wiersma, “The physics and applications of random lasers,” Nat. Phys.4(5), 359–367 (2008). [CrossRef]
  5. B. Redding, M. A. Choma, and H. Cao, “Speckle-free laser imaging using random laser illumination,” Nat. Photonics6(6), 355–359 (2012). [CrossRef]
  6. M. A. Noginov, “Solid-State Random Lasers,” (Springer, Berlin, 2005).
  7. H. Cao, “Lasing in random media,” Waves Random Media13(3), R1–R39 (2003). [CrossRef]
  8. D. S. Wiersma and M. A. Noginov, “Nano and random lasers,” J. Opt.12(2), 020201–024014 (2010). [CrossRef]
  9. J. Andreasen, A. A. Asatryan, L. C. Botten, M. A. Byrne, H. Cao, L. Ge, L. Labonté, P. Sebbah, A. D. Stone, H. E. Türeci, and C. Vanneste, “Modes of random lasers,” Adv. Opt. Photon.3(1), 88–127 (2011). [CrossRef]
  10. M. A. Noginov, N. E. Noginova, H. J. Caulfield, P. Venkateswarlu, T. Thompson, M. Mahdi, and V. Ostroumov, “Short-pulsed stimulated emission in the powders of NdAl3(BO3)4, NdSc3(BO3)4 and Nd:Sr5(PO4)3F laser crystals,” J. Opt. Soc. Am. B13(9), 2024–2033 (1996). [CrossRef]
  11. C. Gouedard, D. Husson, C. Sauteret, F. Auzel, and A. Migus, “Generation of spatially incoherent short pulses in laser-pumped neodymium stoichiometric crystals and powders,” J. Opt. Soc. Am. B10(12), 2358–2363 (1993). [CrossRef]
  12. G. Zhu, T. Tumkur, and M. A. Noginov, “Anomalously delayed stimulated emission in random lasers,” Phys. Rev. A81(6), 065801 (2010). [CrossRef]
  13. J. Azkargorta, M. Bettinelli, I. Iparraguirre, S. García-Revilla, R. Balda, and J. Fernández, “Random lasing in Nd:LuVO4 crystal powder,” Opt. Express19(20), 19591–19599 (2011). [CrossRef] [PubMed]
  14. C. W. Struck and W. H. Fonger, “Dissociation of Eu3+ Charge-Transfer in Y2O2S and La2O2S into Eu2+ and a Free Hole,” Phys. Rev. B4(1), 22–34 (1971). [CrossRef]
  15. R. V. Alves, R. A. Buchanan, K. A. Wickersheim, and E. A. C. Yates, “Neodymium-activated Lanthanum Oxysulfide: A new high-gain laser material,” J. Appl. Phys.42(8), 3043–3048 (1971). [CrossRef]
  16. G. I. Abutalibov, D. I. Guseynov, and A. A. Mamedov, “Nd3+-ion luminescence in La2O2S and Y2O2S single crystals,” Phys. Status Solidi., C Curr. Top. Solid State Phys.6(5), 1127–1129 (2009). [CrossRef]
  17. V. M. Markushev, N. E. Ter-Gabrelyan, Ch. M. Briskina, V. R. Belan, and V. F. Zolin, “Stimulated emission kinetics of neodymium powder lasers,” Sov. J. Quantum Electron.20(7), 773–777 (1990). [CrossRef]
  18. S. García-Revilla, I. Iparraguirre, C. Cascales, J. Azkargorta, R. Balda, M. A. Illarramendi, M. Al Saleh, and J. Fernández, “Random laser performance of NdxY1-xAl3(BO3)4 laser crystal powders,” Opt. Mater.34(2), 461–464 (2011). [CrossRef]
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