Abstract
1. Introduction
Large aperture Nd:phosphate laser glass is at the heart of a high power laser system.
For high peak power inertial confinement fusion (ICF) facility application, there are
many strict technical requirements on laser glass, such as high gain, low nonlinear
refractive index, low attenuation at laser wavelength, excellent optical homogeneity,
and large laser damage threshold. Large aperture Nd:phosphate laser glasses have been
successfully applied in the NIF facility in the United States, and an over
2 MJ ultraviolet laser has already been realized in this largest laser
facility[
Parameters | N31 | LHG-8 | LG-770 | KGSS-0180 |
---|---|---|---|---|
3.8 | 3.6 | 3.9 | 3.6 | |
s | 351 | 365 | 351 | |
/nm | 25.8 | 26.5 | 25.4 | |
d/g/ | 2.87 | 2.83 | 2.59 | 2.83 |
1.540 | 1.5296 | 1.5067 | ||
1.533 | 1.5201 | 1.4991 | ||
Abbe number | 65.8 | 66.5 | 68.4 | |
esu | 1.18 | 1.12 | 1.01 | 1.1 |
Tg/C | 450 | 485 | 460 | 460 |
/K(20–C) | 115 | 115 | 116 | 116 |
dn/dT/10/K | ||||
dS/dT/10/K | 14 | 6 | 11 | |
k/W/m K | 0.56 | 0.58 | 0.57 | |
E/Gpa | 56.4 | 50.1 | 47.3 | 59.0 |
Table 1. Main parameters of neodymium phosphate laser glasses from Hoya[1], Schott[1], Russia (GOI)[4, 9], and SIOM.
2. Compositions and properties of N31 phosphate laser glass
Similar to other neodymium phosphate laser glasses used in an ICF facility, N31 glass is a kind of metaphosphate glass composed of . represents an alkali oxide. MO represents an alkaline oxide. represents mixtures of , , and . Up to 5wt% can be easily doped in N31 glass without obvious change of properties besides density and refractive index. Its composition is satisfied for the requirements of mass fabrication and laser facility applications.
A comparison of the main basic properties of N31 with those of LHG-8, LG-770, and
KGSS-0180 glasses is given in table
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The stimulated emission cross section of N31 glass is higher than that of LHG-8 glass
and close to that of LG-770 glass. In order to suppress the damage from self focus due
to the optical nonlinear effect at high peak energy fluence, the nonlinear refractive
index n of neodymium phosphate laser glass should be controlled. From
Table
The laser gain curves of N3122 and N3130 glasses, with 2.2wt% and 3.0wt% doping concentration, were detected at various xenon lamp pumping
voltages. The fluorescence lifetime and optical loss at 1053 nm will have an
important influence on the small signal gain. Only samples with an optical loss of 0.1–0.15% and a lifetime of 340 s (for 2.2wt%) or 320 s (for 3.0wt% ) were chosen for measurement. The results, shown in
Figure
3. Melting technologies of 400 mm large aperture N31 phosphate laser glass
It is well known that most of the key parameters of laser glass such as fluorescent lifetime, number of platinum inclusions, bubble and optical homogeneity, birefringence, optical attenuation at lasing wavelength, residual , and absorption at 400 nm are determined by the fabrication technology. The fabrication process of a laser glass slab includes melting, forming, rough annealing, fine annealing, and edge cladding. The fabrication technology, especially the melting technology, is very important in ensuring the quality of laser glass. An N31 glass rod with diameter 90 mm and a slab with a clear aperture of 400 mm have been fabricated in SIOM.
The melting technology of N31 glass has been explored since the mid 1990s, and several
fabrication technologies concerning pot melting of N31 laser glass were developed in
early 2000. A patented pot melting technology has been established instead of
traditional two-step melting[
High purity raw materials with Fe, Cu, Cr, Ni, and V trace elements (less than
3 ppm) have been domestically fabricated. Through the controlling of the
purity of raw materials and melting processing, the total amount of transition metal
oxides is less than 10 ppm in N31 glass. Research has been done on the effect of Fe and
Cu impurities on the optical attenuation of N31 glass[
The pot melting efficiency is too low to manufacture thousands of laser glass slabs.
Since 2006, research on continuous melting technology of N31 glass has been carried out.
The continuous melting technology of large aperture laser glass is more complicated than
that of traditional optical glass due to its special technical parameters. Based on the
matured laser glass fabrication technology of pot melting[
The continuous melting line of N31 laser glass consists of an interconnected melter,
conditioner, refiner, homogenizer, forming, and annealing lehr. Figure
Parameters | Data |
---|---|
Attenuation at 1053 nm | 0.10–0.14% |
Fluorescent lifetime (s) | 310–315 |
n | 1.540 0.001 |
Absorption coefficient at 400 nm | 0.12–0.23 |
Absorption coefficient at () | 0.5-1.8 |
Optical homogeneity | 2 |
Platinum inclusion | No platinum for more than 80% glass slabs |
Damage threshold at 1064 nm, 3 ns | No bulk damage at energy influence |
Table 2. Parameters of mass production N3135 glass.
Table
In the measurement of the single shot laser induced bulk damage threshold (bulk LIDT),
ISO 11254-1 was taken as a standard[
Figure
A typical 633 nm transmitted wavefront of 400 mm aperture N3135
laser glass, which was measured by Zygo interferometer with a test aperture of
600 mm, is shown in Figure
4. Edge cladding of N31 phosphate laser glass
Edge cladding is an important technology to suppress the amplified stimulated emission ASE and to ensure the gain properties of large size Nd:phosphate glass. ion doped phosphate glass with a precise refractive index match to N31 laser glass has been designed as a cladding glass. A kind of self-developed epoxy adhesive agent with precise refractive index match to both the laser glass and the cladding glass is used to bond these two glasses. It provides an adhesive strength of 18 MPa. This adhesive agent has been tested to be highly resistant to high intensity pump and laser power as well as humid environments in the polishing process.
The doping level is limited by the temperature rise at the interface between the cladding glass and the laser glass. This temperature rise is due to strong absorption of ASE energy of a laser pulse. The temperature rise after a laser shot can be expressed by
A patented edge cladding technique has been developed for large aperture N31 laser
glass[
The residual stress caused by edge cladding is kept small by the proper choice of
adhesive agent and its curing parameters. Figure
Figure
5. Conclusions
The main composition and properties of N31 Nd-doped phosphate laser glass are reported. Three key techniques for laser glass fabrication (pot melting, continuous melting, and edge cladding) have been developed in Shanghai Institute of Optics and Fine Mechanics. The glass parameters and laser gain of N3135 phosphate glass produced by continuous melting are almost the same as those obtained by pot melting. 400 mm clear aperture N31 glass slabs with high quality have been fabricated for building the Shen Guang high peak power laser facilities in China.
References
[1] J. H. Campbell, T. I. Suratwala. J. Non-Cryst. Solids, 263&264, 318(2000).
[2] E. Hand.
[3] J. H. Campbell, T. I. Suratwalaa, C. B. Thorsnessa, J. S. Haydenb, A. J. Thorneb, J. M. Ciminob, A. J. Marker IIIb, K. Takeuchic, M. Smolleyc, G. F. Ficini-Dornd. J. Non-Cryst. Solids, 263&264, 342(2000).
[4] V. I. Arbuzov, Y. K. Fyodorov, S. I. Kramarev, S. G. Lunter, S. I. Nikitina, A. N. Pozharskii, A. V. Shashkin, A. D. Semyonov, V. E. Ter-Nersesyants, A. V. Charukhchev, V. S. Sirazetdinov, S. G. Garanin, S. A. Sukharev. Glass Technol., 46, 67(2005).
[5] Z. Jiang. Chin. J. Lasers, 33, 1265(2006).
[6] Y. Jiang, J. Zhang, W. Xu, Z. Ma, X. Ying, H. Mao, S. Mao, J. Li. J. Non-Cryst. Solids, 80, 623(1986).
[7] L. Hu, Z. Jiang. Bull. Chin. Ceramics Society, 25, 125(2005).
[8] L. Hu, S. Chen, T. Meng, W. Chen, J. Tang, B. Wang, J. Hu, L. Wen, S. Li, Y. Jiang, J. Zhang, Z. Jiang. High power laser and particle beams, 23, 2560(2011).
[9] V. I. Arbuzov, Yu. K. Fedorov, S. I. Kramarev, A. V. Shashkin. J. Opt. Technol., 80, 321(2013).
[10] J. Zhang, H. Mao, S. Chen, X. Ying, B. Wang, B. Zhou, H. Zhu, C. Jin.
[11] Y. Xu, S. Li, L. Hu, W. Chen. Chin. Opt. Lett., 3, 701(2005).
[12] Y. Xu, S. Li, L. Hu, W. Chen. J. Rare Earths, 29, 614(2011).
[13] D. Zhuo, W. Xu, Y. Jiang. Chin. J. Laser, 12, 173(1985).
[14] B. Zhou, L. Hu, Y. Jiang, H. Mao, J. Zhang. Chin. J. Lasers, 28A, 837(2001).
[15] J. Tang, L. Hu, F. Gan. J. Wuhan Univ. Technol., 29, 210(2007).
[16] J. Tang, L. Hu, X. Ying, C. Jin, F. Gan. Glass & Enamel (Monograph), 30(2007).
[17] J. Tang, B. Wang, L. Hu. Annual Reports on Inertial Confinement Fusion of China Academy of Engineering Physics(2011).
[18]
[19] J. Schwider, R. Burow, K.-E. Elssner, R. Spolaczyk. J. Grzanna, Appl. Opt., 24, 3059(1985).
[20] T. Meng, J. Tang, J. Hu, L. Wen, L. Chen, W. Chen, L. Hu.
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