Luminescence in the fluoride-containing phosphate-based glasses: A possible origin of their high resistance to nanosecond pulse laser-induced damage

Abstract

Fusion power offers the prospect of an almost inexhaustible source of energy for future generations. It was reported that fusion fuel gains exceeding unity on the National Ignition Facility (NIF) were achieved, but so far great deal of scientific and engineering challenges have to be overcome for realizing fusion power generation. There is a bottleneck for color-separation gratings in NIF and other similar inertial confinement fusion (ICF) lasers. Here we show a series of high performance phosphate-based glasses that can transmit the third harmonic frequency (3ω) laser light with high efficiency meanwhile filter the fundamental (1ω) and the second harmonic frequency (2ω) laser lights through direct absorption, and especially they exhibit excellent damage threshold induced by nanosecond pulse laser compared with that of the fused silica used in NIF. Yellowish-orange fluorescence emits during the laser-material interaction process, and it can be tailored through regulating the glass structure. Study on its structural origin suggests that the fluorescence emission is a key factor that conduces to the high laser-induced damage resistance of these glasses. The results also indicated the feasibility of utilizing these high performance glasses in novel color separation optics, allowing novel design for the final optics assembly in ICF lasers.

Investigations on the photoluminescence spectra and its defect-related nature for the ultraviolet transmitting fluoride-containing phosphate-based glasses

“…These structural defects were formed during the preparation process due to the addition of metal cations [31,40,41], which have an intense absorption in the ultraviolet and part of the VIS region and therefore can be indentified through analysis on the optical transmission and absorption spectra. The obvious blue-shift of the UV absorption edge of sample A is associated with the reducing glass melting atmosphere that will suppress the formation of Fe 3+ impurity and decrease the concentration level of PO 3 2 − defects in the glass which have absorption in the UV region [1,20]. Besides, the slight decline of the transmittance in the range of the short wavelength was observed for sample C and D as compared with that of sample A and B, respectively.…”

“…However, the intensity of the emission at 505 nm becomes lower after thermal treatment in H 2 , which may be due to part of the POHC defects that has transformed into PO 4 3− under the effect of hydrogen atoms, because they have high structural similarity [31,32]. In our previous works, the kind of glass manufactured under the reducing atmosphere showed a broad fluorescence band centered close to 780 nm under the high energy 351 nm pulse laser irradiation, however the other type of glass prepared without any reducing atmosphere, i.e., at the ambient air condition, did not give any detectable fluorescence under the same laser irradiation condition [20]. For comparison, we also monitored the PLE spectra under monitoring at 780 nm for these two series of glass samples before and after the thermal treatment in hydrogen (see Figs.…”

“…Nevertheless, it isn't clear. More recently, we have just reported a new series of ultraviolet transmitting fluoride-containing phosphate-based glasses with high pulse laserinduced damage thresholds (LIDTs), and proposed that the distinct laser-induced fluorescence phenomenon with a character of eye- visible laser-induced fluorescence emission might be a key factor conducing to the high laser-induced damage resistance of these glasses [20]. To understand the interrelationship between the laser-induced fluorescence, formation of transient defects and the glass microstructure is necessary for further regulation of the glasses' LIDTs, before which study on the intrinsic defects in these glasses should go in advance.…”

“…To achieve a higher UV transmission, it is necessary to minimize the Fe 3+ content in the glasses. One way is to use the ultra-high purity raw materials with low iron content, another, to reduce Fe 3+ into Fe 2+ through a reducing glass melting conditions [13,[18][19][20].…”

Automatic classification of true and false laser-induced damage in large aperture optics

“…Laser-induced damage is easily generated under 351-nm high-power laser irradiation. [1][2][3] When the number of damaged sites increases to a certain magnitude, these sites modulate the high-power UV lasers in ICF experiments, thereby significantly affecting the beam quality. [4][5][6][7] The best way to rapidly and efficiently detect and track the damage on an FOA surface is to design an online imaging system for observing tiny defects in the center of the target chamber.…”