Open Access
Add to BibSonomy
Abstract
We propose a strategy to optimize the laser conditioning of DKDP crystals by varying the temporal shape of sub-nanosecond pulses. Four sub-ns temporally shaped pulses with nearly the same full width at half maxima of ∼600 ps but different rising-falling statuses were designed to conduct laser-induced damage (LID) and laser conditioning experiments on DKDP crystals. The shape of the pulse substantially influences the damage pinpoints size and LID threshold (LIDT) of the crystals in the sub-nanosecond range. After sub-nanosecond laser conditioning, the ns R-on-1 LIDT showed that slow-rising fast-falling pulse (R400-F200 and High-foot pulses) conditioning achieved a 14%-20% LIDT enhancement than the traditional Gaussian pulse (R300-F300 pulse). The 8-ns laser damage morphologies after slow-rising fast-falling pulse conditioning showed cracks, whereas those after fast-rising slow-falling pulse (R200-F400 pulse) conditioning were pinpoint core, as usual. These results suggest that the rising front plays an important role in the LID and laser conditioning of the DKDP crystals. A pulse with a slower rising front is beneficial for thermal modification, thereby leading to better LID properties. This strategy greatly expands and enriches the manipulation methods to improve the LIDT of DKDP crystals, and sheds light on understanding the laser damage mechanisms.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Crystals of potassium dihydrogen phosphate (KDP) and its deuterated analog (DKDP) are currently irreplaceable nonlinear optical materials suitable for frequency conversion and polarization beam control in high-power large-aperture laser systems. However, laser-induced damage (LID) occurring in these crystals adversely affects the quality of the downstream beam, which has attracted considerable research attention [1,2]. Recent studies reported that “damage precursors” formed during growth and preparation procedures are responsible for material breakdown because of light absorption at the nanosecond laser [3–5].
Various types of bulk precursors, such as inclusions, impurity ions [6], and intrinsic electronic defects [7–10], could induce enhanced absorption, contributing to the change in the LID of KDP/DKDP crystals. For example, first principle calculations for hydrogen point defects in KDP proved that the band gaps of the positively charged H vacancy and neutral interstitial H considerably reduce to 2.5 and 2.6 eV [8,9]. Carr et al. studied the wavelength dependence of the LID threshold (LIDT) and suggested that the photon energy plays an important role in multiphoton absorption and alters the defect-assisted damage mechanism in KDP crystals [11]. A simple model based on heat transfer [12] demonstrated that only point defect clusters with specific dimensions can produce a sufficiently high temperature, causing LID. Reyné et al. studied the influence of crystal orientation on LID, suggesting the geometry and anisotropy of precursors in KDP crystals [13]. However, current growth techniques still failed to eliminate defects thoroughly, even for those of almost “invisible” size and/or concentration [14,15].
Moreover, the precursors responsible for LID are not yet well understood. Laser conditioning is a generalized method that improves the LIDT of KDP/DKDP crystals and has been applied for over two decades [16,17]. Demange et al. found two types of precursors initiating damage in two different spectral ranges (1,064 and 532/355 nm) and declared that conditioning for pre-exposure occurs only when using wavelengths equal to or shorter than the wavelength used for operation [18–20]. Liao et al. proposed an absorption distribution model showed that a nanosecond laser plays a role in one of two populations of absorbing defects in the DKDP crystal, one with nonlinear absorption and the other with linear absorption [21,22]. Adams et al. performed conditioning experiments with a 355-nm laser at pulse lengths of 300–860 ps to increase the damage performance by ∼2.5 times, which is the best conditioning result for DKDP crystals [23,24]. Recent research on fused silica showed that the Gaussian truncated pulses enhanced laser conditioning better than the Gaussian pulse [25]. DKDP crystals, as a transparent optical material with similar size characteristics of damage precursors to fused silica, also exhibited differences with various temporal pulse shapes. For instance, the LIDT induced by the flat-in-time-pulse laser was less than 80% of that induced by the Gaussian pulse, with the same full width at half maximum (FWHM) and fluence [26]. However, the influence of varying pulse shape on the laser conditioning of DKDP crystals has not been studied yet.
Therefore, in this work, we used four temporally shaped pulses with different rising and falling edges and the FWHMs of ∼600 ps as an experimental strategy to study this problem. First, sub-ns LID and ns LID conditioned by the sub-ns temporally shaped pulses were conducted. Second, scanning electron microscopy (SEM) was used to observe the morphological characteristics of damage pinpoints, including those induced by temporally shaped pulses directly and those induced by an 8-ns laser after temporally shaped laser conditioning. Finally, we established a method using the sub-ns laser with a slow-rising pulse front to optimize the sub-ns laser conditioning of DKDP crystals, which resulted in a 20% improvement compared with the conventional Gaussian pulse conditioning. The reasons for the difference in the LIDT and damage morphology caused by the pulse shape are discussed. Additionally, the influence of the temporal shape on the laser damage and conditioning is revealed.
2. Experimental details
2.1 Experimental sample
The DKDP sample was cut from a “point-seed” rapid growth boule [27,28]. The sample was type-II matched for third-harmonic generation. The sample dimensions were 100 mm × 100 mm × 10 mm, and it was polished to attain optical quality on all sides.
The Raman spectrum was characterized using an HR Evolution & FLS980 ultrafast transient spectrometer to evaluate the deuteration rate of the DKDP samples. A 532-nm continuous laser was selected as the excitation source, and the test range was 500–2500 cm-1. A Lambda 1050 UV-VIS-NIR spectrophotometer was adopted to measure the transmittance spectrum of the DKDP crystals, with a 1-nm spectral resolution and accuracy of ± 0.5 nm. We divided the sample into four areas as shown in the inset in Fig. 3 and randomly selected four test points to estimate the average value in each area to examine the transmittance homogeneity of the DKDP sample.
2.2 Experimental setup
Figure 1 shows a schematic of the laser damage and laser conditioning experimental setup. The pulse emitted by the sub-ns laser system was adjusted using an energy attenuator, which comprised a half-wave plate and polarizer. The beam was focused on the sample through the lens with the focal length of 4.5 m. The effective area of the laser spot on the sample was 0.1 ± 0.01 mm2, measured using the beam diagnostic constituting two splitters and a beam profiling instrument (LaserCam HR). Bulk damage in the DKDP crystal was illuminated using an He-Ne laser that was collinear with the damage beam and diagnosed in real time using a CCD placed orthogonally toward the laser propagation direction.
When the laser source was replaced with an Nd:YAG laser having 8-ns Gaussian temporal profile pulse, the experimental setup demonstrated in Fig. 1 was employed for the nanosecond laser damage test. The effective area of the ns laser spot on the target was 0.3 mm2. In addition, the laser beams used in this work are all the Gaussian profiles in spatial distribution.
Temporally shaped pulses were generated by the sub-ns laser system, a detailed description of which is provided in Ref. [29]. A commercial single-longitudinal-mode fiber laser with an arbitrary waveform generator (AWG), supplied seed pulses at the repetition rate of 100 Hz and wavelength of 1,064 nm. The commercial single-longitudinal-mode fiber laser allowed accurate tuning of the output wavelength by changing the temperature of the distributed feedback seed laser. After passing through the master oscillator power amplifier and two cascaded LBO nonlinear crystals, the output pulse was converted into an ultraviolet laser at 355 nm.
Firstly, we determined that the full width at half maximum (FWHM) of sub-ns laser used in this study is 600 ps. Then the time when the pulse reaches the peak power was adjusted in AWG, including fast-arrival type, medium-arrival type, and slow-arrival type (both fast- and slow-arrival types are required to reach the extreme). After many times of debugging, three temporally shaped pulses used in this paper are obtained, as illustrated in Fig. 2. According to the pulse width at half maximum of rising edge and falling edge, we named the fast-arrival type, medium-arrival type and slow-arrival type as the R200-F400 pulse, the R300-F300 pulse and the R400-F200 pulse, respectively. In addition, a low-power section is added to the rising edge of the R400-200 pulse, becoming a combined pulse named High-foot pulse.
Fig. 2. Four types of temporally shaped pulses with FWHM of ∼ 600 ps and an 8 ns Gaussian pulse laser. The figure in the lower right corner is the spot distribution of sub-ns and ns lasers.
2.3 Laser damage testing and laser conditioning
The experimental procedure was divided into three primary parts: the sub-ns laser damage test, ns laser damage test on the sub-ns laser conditioning area, and damage morphology analysis.
First, the LIDTs of the sample by the four temporally shaped pulses were tested using the R-on-1 protocol, seen in Ref. [30] for the details. Approximately 40 sites were calculated for each pulse shape. The laser fluence shot to each site started from 0.5 J/cm2 and ramped by 0.5 J/cm2 until the damage pinpoint appeared.
Second, pristine regions on the sample were raster-scanned with each temporally shaped pulse. The overlap of laser spots was maintained above 90% by adjusting the moving speed of the sample, which was mounted on a motorized x-y translation stage. The scanning areas of every temporally shaped pulse were 10 mm × 17 mm. The conditioning fluence was also started with 0.5 J/cm2 and continuously ramped by 0.5 J/cm2. The final conditioning fluences in this study reached 4.5 J/cm2 for the R200-F400 and R300-F300 pulses, and 6.0 J/cm2 for the R400-F200 and high-foot pulses. Then, the ns LIDT of the conditioned regions and pristine region were tested using the R-on-1 protocol.
Finally, the bulk damage pinpoints were etched and exposed to distilled water and high concentrations of ethanol. The exposed damage pinpoints were then assessed via field emission SEM, with ∼5 nm of evaporated carbon, to enhance the electrical conductivity, and 1.0–3.0-KeV electrons were employed for the image.
3. Results and discussion
3.1 Optical properties of DKDP crystals
The transmittance spectrum presented Fig. 3 (a) depicts the same transmission of the four areas in the UV-VIS-NIR band, indicating that the DKDP crystal was uniform in light absorption. The defect cluster concentration in the prismatic and pyramidal sectors varies based on the crystal growth method [31]. A DKDP crystal grown in the prismatic sector attracts more impurity ions, resulting in enhanced ultraviolet absorption and low transmittance. Therefore, the small quantities of absorption in the ultraviolet band proved that the DKDP samples are cut from the pyramidal sector of the crystal boule.
Figure 3 (b) illustrates the corresponding Raman spectrum. With an increase in the deuterium content in DKDP, the position of the vibration peak of PO4 splits off and shifts significantly [32]. Therefore, using the shift value of the vibrational peak of PO4 to a shorter wavenumber, the deuterium content of DKDP crystals in work is about 63%.
3.2 Sub-ns laser-induced damage (LID) under different temporally shaped pulses
Figure 4 presents the sub-ns LID results. The LIDTs by different temporally shaped pulses are distinct from those obtained by the R300-F300 pulse, which is similar to the conventional Gaussian temporal profile pulse, resulting in the LIDT of 5.5 J/cm2. The maximum LIDT is 6.0 J/cm2, caused by both the R400-F200 and the high-foot pulses. The minimum LIDT caused by the R200-F400 pulse is 5.0 J/cm2. Combined with the shape of the temporally shaped pulse shown in Fig. 2, we found that the R200-F400 and R300-F300 pulses with faster rising edges led to similar lower LIDTs. Because the rising edge of the R400-F200 pulse is slower (or longer) than that of the R200-F400 and R300-F300 pulses, it results in a larger LIDT. The high-foot pulse with the slowest rising edge also produces a large LIDT, and its fluence at 100% damage probability was far greater than that of the R400-F200 pulse. For R200-F400 and R300-F300 pulses, only lower laser fluence was needed for the same damage degree. Thus, damage to the DKDP crystal is more sensitive to the laser with a fast-rising pulse front compared with other shaped pulses.
3.3 ns-LID after different temporally shaped pulse conditioning
The LIDTs by the 8-ns laser were conducted on the unconditioned and four temporally shaped pulse-conditioned regions of the DKDP crystal, as displayed in Fig. 5. As can be seen, the R-on-1 damage performances all show improvement to higher fluence after sub-ns temporally shaped pulse conditioning.
Fig. 5. R-on-1 damage probabilities in 8-ns Gaussian pulse, tested after laser conditioning with different temporally shaped pulses.
The LIDT by the R300-F300 conditioning is 23.7 J/cm2, which is 40% higher than that of the pristine region in the DKDP crystal. The LIDTs by the R400-F200 and high-foot pulse conditioning are 28.6 and 27.1 J/cm2, which are 20% and 14% higher than those by the R300-F300 pulse conditioning, respectively. The LIDT of the R200-F400 pulse conditioning is 21.9 J/cm2, which is 8% lower than that of R300-F300 pulse conditioning. The 50% probability damage results display ∼1.14, ∼1.30, ∼1.16, and ∼1.25× improvements in fluence after conditioning compared to the pristine one. These improvements, particularly those conditioned by the R300-F300, R400-F200, and R200-F400 pulses, were consistent with the sub-ns LIDTs in sequence. The results demonstrate that a sub-ns laser with a slow-rising pulse front is beneficial for laser conditioning. However, although the high-foot pulse is superior to the R400-F200 pulse in terms of damage characteristics, the conditioning result is inferior. This is a new result and implies that not the slower the rising edge, the better the laser conditioning.
3.4 Sub-ns laser damage morphology
To investigate the influence of temporally shaped pulses on the LID behavior and laser conditioning of the DKDP crystal, the damage morphologies were carefully studied. Figure 6 demonstrates the typical morphology of damage pinpoints induced by different temporally shaped pulses. All the pinpoints show properties similar to those of spherical cavities or circular cores with sizes ranging from tens to one- or two-hundred nanometers.
Fig. 6. SEM images of typical damage morphologies of the DKDP crystal under different temporally shaped pulses. The used irradiation pulse and laser fluence are marked in the upper right corner of each image.
Because the resolution of the CCD in the online damage detection system is at the micron level, it is not feasible to detect pinpoints with sizes ranging from tens to hundreds of nanometers. The damage pinpoint at a lower energy density could be accurately captured via SEM with nanoscale resolution, compared with the CCD detection results. Similarly, some damage morphologies under the ns laser below the given LIDT fluence were also obtained (Fig. 9).
To analyze the size of the damage pinpoints, the distributions presented in Fig. 7 and Fig. 8 were calculated by <d> ±2σ, where <d> = Σdini/N, di is a bin of a particular diameter, ni is the number of diameters that fall within that particular bin, N is the total number of measured diameters, and 2σ = $2\sqrt {\left\langle {{d^2}} \right\rangle - {{\left\langle d \right\rangle }^2}} $.
Fig. 7. Size distribution of damaged pinpoints irradiated by the R400-F200 pulse under various fluences.
Fig. 8. Size distribution of damaged pinpoints irradiated by temporally shaped pulses when the fluence is 4.0 J/cm2.
The sizes of the pinpoints induced at higher fluence are larger, as shown in Fig. 7 with diameters in the ranges of 48 ± 33.4, 60.6 ± 15.5, and 191.6 ± 176.8 nm. In Fig. 8, the damage pinpoints induced by the R300-F300 pulse laser at 4 J/cm2 exhibit the diameter range of approximately 205 ± 91.1 nm, while the diameter ranges of the pinpoints induced by the R400-F200, R200-F400, and high-foot pulses are 60.6 ± 15.5, 138 ± 117.6, and 52.9 ± 56.6 nm, respectively. The morphologies, however, are quite different from those in previous studies [33,34] which showed that the damage pinpoint morphology under a 355-nm laser in 3 ns consists of two distinct regions: a core with a size of several microns and a region of the modified area surrounding the core. This indicates that the laser pulse width, that is, the reaction time between the laser and precursors, will affect the LID processes. Compared with the ns laser, the action time of the sub-ns laser is considerably short, which does not lead to a significant heat diffusion. Thus, no modified area is formed around the damaged core.
3.5 Nanosecond laser damage morphology
Figure 9 illustrates the damage morphologies under the 8-ns and 23-J/cm2 lasers. The bulk damage site on the pristine region primarily comprises a core, a region of modified material surrounding the core, and a few radial cracks spreading the core. The core is approximately 8.5 μm in size, and there are many cleavage microstructures formed by the thermal stress along the inner wall. The damage pinpoints in the area pre-exposed by the R200-F400 and R300-F300 pulses are similar to those in the pristine area but with a core size of 3–5 μm. Nevertheless, the damage pinpoint morphologies that were pre-exposed to R400-F200 and high-foot pulses are quite different from those exposed to the pristine ones, which exhibit longer radial cracks of more than ten microns and less clear cores. Furthermore, the core could no longer be observed after R400-F200 pulse conditioning. Figure 9 shows the distinct degrees of modification with sub-ns laser conditioning.
Fig. 9. SEM images of typical damage morphology initiated with 8-ns and 23-J/cm2 laser. The laser conditioning parameters are marked in the upper right corners of (a)–(e). Images with an arrow and the insets in (a)–(c) indicate the damage morphologies detected via the optical microscopy.
3.6 Discussion
From the perspective of the laser conditioning mechanism, two models were established to explain the improvement in laser damage resistance of the DKDP crystal. One named the thremal absorption model holds that laser conditioning could lead to the phase transformation and recrystallization of the lattaces with defects, thereby reducing the absorption of defects in DKDP crystals [35]. The other one related to the defect-assisted multiphoton absorption model holds that the electronic structure of defects is changed by electrons or holes produced by conditioning laser irradiation, which results in the elimination or change of the energy state in the band gap and reduces the ionization probability [36]. After sub-ns laser conditioning, the 8-ns laser damage test showed improved overall laser damage resistance of the DKDP crystal. Slow-rising fast-falling pulse (R400-F200 and High-foot pulses) conditioning achieved an improvement of more than 10 J/cm2 compared with the pristine LIDT, while fast-rising slow-falling pulse (R200-F400 and R300-F300 pulses) conditioning showed an improvement of only 5–7 J/cm2. In addition, sub-ns laser conditioning greatly influences the morphology of 8-ns laser damage. The 8-ns laser damage morphologies after slow-rising fast-falling pulse conditioning exhibited a radial crack with a size of more than ten microns, whereas that after fast-rising slow-falling pulse conditioning still exhibited a pinpoint core, reduced in size. This result is similar to the experimental results of the LIDT and laser conditioning of the TrG and R-TrG pulses in the study conducted by Kafka et al. [25] and provides strong support for the first laser conditioning mechanism model as mentioned above. The change of ns laser damage morphologies is obviously due to the thermal modification of the material. After heating by the laser, the defects are dispersed in the host, and then the concentration of defect points becomes lower and the absorption becomes weaker [37]. Moreover, many literatures believe that the second model exists at the same time [11,14,38], but the specific research needs more experiments in future.
The LIDT and damage probability curves indicate that the shape of the pulse greatly affects the laser damage behavior of crystals in sub-ns regime. Slow-rising fast-falling pulse have higher sub-ns LIDT, as well as lower damage probabilities under high fluence laser (such as 8 J/cm2), than fast-rising slow-falling pulse. In addition, the sizes of the damaged pinpoints caused by the two groups of pulses with the same fluence are significantly different. The pinpoint sizes caused by slow-rising fast-falling pulse are primarily distributed in the range of 50–60 nm, while those caused by fast-rising slow-falling pulse are concentrated in the range of 100–200 nm. In a manner of speaking, the slow-rising fast-falling sub-ns pulse causes lesser damage to the crystal than the fast-rising slow-falling pulse. Moreover, during the sub-ns laser conditioning, the maximum fluence steps achieved by the two groups of pulses are 6.0 and 4.5 J/cm2, respectively. Specifically, the slow-rising fast-falling sub-ns pulse produced less damage, which was beneficial to the promotion of the maximum fluence step during laser conditioning. Consequently, the ns laser damage resistance of DKDP crystals can be further improved.
Based on the difference of the sub-ns LIDTs, the maximum fluence during sub-ns laser conditioning, and the ns-LIDTs of DKDP crystals after laser conditioning, we propose that the absorption dynamics for the laser irradiation process in DKDP not only involves damage initiation in the host material, but also drives the non-damage process of laser conditioning of defects. The dominance between them in the irradiation process depends on the rising speed of the pulse front. The fast-rising rate of the laser front can contribute to the damage initiation, and the slow-rising leading edge will give rise to a better laser conditioning. This also explains the results that the LIDT by the flat-in-time-pulse laser is lower than that of Gaussian pulse with the same FWHM in Ref. [26]. The ns laser damage morphologies by the slow-rising fast-falling pulse conditioning displayed large cracks and no local damage pinpoint, indicating that this type of pulse causes the heat modification more thoroughly and drives the non-damage process of laser conditioning in the absorption dynamics. In addition, the maximum fluence of slow-rising fast-falling pulse is obviously higher than that of fast-rising slow-falling pulse during laser conditioning. All these results proved that slow-rising pulse edge drives the laser conditioning, which is a no-damage process in the absorption dynamics.
4. Conclusion
Herein, we presented a comprehensive study of the influence of temporal shape on the LID and laser conditioning of DKDP crystals. R400-F200, R300-F300, R200-F400, and High-foot pulses with the same FWHM of ∼600 ps but different rising–falling statuses were employed to conduct the experiments.
The results of the temporally shaped nanosecond LID test indicated that a slow-rising fast-falling pulse (R400-F200 and High-foot pulses) with the same fluence caused less damage, and led to a higher sub-ns LIDT and smaller damage pinpoint size. After slow-rising fast-falling pulse laser conditioning, the ns LIDTs improved by 20% (R400-F200 pulse) and 14% (High-foot pulse), compared with the traditional Gaussian pulse conditioning, i.e., R300-F300 pulse conditioning. The ns laser damage morphologies after slow-rising fast-falling pulse conditioning exhibited cracks, whereas that after fast-rising slow-falling pulse conditioning was pinpoint core, as usual. This is because a slow-rising fast-falling pulse leads to a better thermal modification of the DKDP materials.
Therefore, a method, which uses a pulse with a slower rising edge as the conditioning laser, was proposed to improve the resistance to LID. This work can be utilized to enhance laser conditioning and achieve better control of the energy deposition process and the resulting precursor modification.
Funding
National Key R&D Program of China (Grant no. 2018YFE0115900); National Natural Science Foundation of China (11874369, U1831211); Strategic Priority Research Program of the Chinese Academy of Sciences (XDB1603); CAS special research assistant project.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. J. De Yoreo, A. Burnham, and P. Whitman, “Developing KH2PO4 and KD2PO4 crystals for the world's most power laser,” Int. Mater. Rev. 47(3), 113–152 (2002). [CrossRef]
2. H. Yang, J. Cheng, Z. Liu, Q. Liu, L. Zhao, C. Tan, J. Wang, and M. Chen, “Potential damage threats to downstream optics caused by Gaussian mitigation pits on rear KDP surface,” High Power Laser Sci. Eng. 8, 04000e04037 (2020). [CrossRef]
3. M. D. Feit and A. M. Rubenchik, “Implications of nanoabsorber initiators for damage probability curves, pulselength scaling and laser conditioning,” in Laser-Induced Damage in Optical Materials: 2003, G. J. Exarhos, A. H. Guenther, N. Kaiser, K. L. Lewis, M. J. Soileau, and C. J. Stolz, eds. (Spie-Int Soc Optical Engineering, Bellingham, 2003), pp. 74-82.
4. T. A. Laurence, R. A. Negres, S. Ly, N. Shen, C. W. Carr, D. A. Alessi, A. Rigatti, and J. D. Bude, “The role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II. Scaling laws and the density of precursors,” Opt. Express 25(13), 15381–15401 (2017). [CrossRef]
5. G. Duchateau, “Simple models for laser-induced damage and conditioning of potassium dihydrogen phosphate crystals by nanosecond pulses,” Opt. Express 17(13), 10434–10456 (2009). [CrossRef]
6. A. K. Burnham, M. Runkel, M. D. Feit, A. M. Rubenchik, R. L. Floyd, T. A. Land, W. J. Siekhaus, and R. A. Hawley-Fedder, “Laser-induced damage in deuterated potassium dihydrogen phosphate,” Appl. Opt. 42(27), 5483–5495 (2003). [CrossRef]
7. S. D. Setzler, K. T. Stevens, L. E. Halliburton, M. Yan, N. P. Zaitseva, and J. J. DeYoreo, “Hydrogen atoms in KH2PO4 crystals,” Phys. Rev. B 57(5), 2643–2646 (1998). [CrossRef]
8. C. S. Liu, N. Kioussis, S. G. Demos, and H. B. Radousky, “Electron- or hole-assisted reactions of H defects in hydrogen-bonded KDP,” Phys. Rev. Lett. 91, 4 (2003). [CrossRef]
9. C. S. Liu, Q. Zhang, N. Kioussis, S. G. Demos, and H. B. Radousky, “Electronic structure calculations of intrinsic and extrinsic hydrogen point defects in KH2PO4,” Phys. Rev. B 68, 11 (2003). [CrossRef]
10. N. Garces, K. Stevens, L. Halliburton, S. G. Demos, H. Radousky, and N. Zaitseva, “Identification of electron and hole traps in KH 2 PO 4 crystals,” J. Appl. Phys. 89(1), 47–52 (2001). [CrossRef]
11. C. W. Carr, H. B. Radousky, and S. G. Demos, “Wavelength dependence of laser-induced damage: Determining the damage initiation mechanisms,” Phys. Rev. Lett. 91, 4 (2003). [CrossRef]
12. G. Duchateau and A. Dyan, “Coupling statistics and heat transfer to study laser-induced crystal damage by nanosecond pulses,” Opt. Express 15(8), 4557–4576 (2007). [CrossRef]
13. S. Reyne, G. Duchateau, J.-Y. Natoli, and L. Lamaignere, “Laser-induced damage of KDP crystals by 1 omega nanosecond pulses: influence of crystal orientation,” Opt. Express 17(24), 21652–21665 (2009). [CrossRef]
14. S. G. Demos, P. DeMange, R. A. Negres, and M. D. Feit, “Investigation of the electronic and physical properties of defect structures responsible for laser-induced damage in DKDP crystals,” Opt. Express 18(13), 13788–13804 (2010). [CrossRef]
15. Y. Wang, Y. Zhao, X. Peng, G. Hu, M. Zhu, and J. Shao, “Influence of the size and concentration of precursor on laser damage performance in KDP crystal,” in Laser-Induced Damage in Optical Materials 2016, (International Society for Optics and Photonics, 2016), 100141 T.
16. M. Runkel, J. DeYoreo, W. Sell, and D. Milam, “Laser conditioning study of KDP on the Optical Sciences Laser using large area beams,” in Laser-Induced Damage in Optical Materials: 1997, Proceedings, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, eds. (Spie-Int Soc Optical Engineering, Bellingham, 1998), pp. 51-63.
17. Y. Wang, Y. Zhao, G. Hu, X. Peng, J. Chang, X. Xie, J. He, M. Guo, and J. Shao, “Mitigation of scattering defect and absorption of DKDP crystals by laser conditioning,” Opt. Express 23(12), 16273–16280 (2015). [CrossRef]
18. P. DeMange, C. W. Carr, R. A. Negres, H. B. Radousky, and S. G. Demos, “Multiwavelength investigation of laser-damage performance in potassium dihydrogen phosphate after laser annealing,” Opt. Lett. 30(3), 221–223 (2005). [CrossRef]
19. P. DeMange, R. A. Negres, C. W. Carr, H. B. Radousky, and S. G. Demos, “Laser-induced defect reactions governing damage initiation in DKDP crystals,” Opt. Express 14(12), 5313–5328 (2006). [CrossRef]
20. P. DeMange, R. A. Negres, H. B. Radousky, and S. G. Demos, “Differentiation of defect populations responsible for bulk laser-induced damage in potassium dihydrogen phosphate crystals,” Opt. Eng. 45(10), 104205 (2006). [CrossRef]
21. Z. M. Liao, M. L. Spaeth, K. Manes, J. J. Adams, and C. W. Carr, “Predicting laser-induced bulk damage and conditioning for deuterated potassium dihydrogen phosphate crystals using an absorption distribution model,” Opt. Lett. 35(15), 2538–2540 (2010). [CrossRef]
22. Z. M. Liao, R. Roussell, J. J. Adams, M. Runkel, W. T. Frenk, J. Luken, and C. W. Carr, “Defect population variability in deuterated potassium di-hydrogen phosphate crystals,” Opt. Mater. Express 2(11), 1612–1623 (2012). [CrossRef]
23. J. J. Adams, T. L. Weiland, J. R. Stanley, W. D. Sell, R. L. Luthi, J. L. Vickers, C. W. Carr, M. D. Feit, A. M. Rubenchik, M. L. Spaeth, and R. P. Hackel, “Pulse length dependence of laser conditioning and bulk damage in KD2PO4,” in Laser-Induced Damage In Optical Materials: 2004, G. J. Exarhos, A. H. Guenther, N. Kaiser, K. L. Lewis, M. J. Soileau, and C. H. Stolz, eds. (Spie-Int Soc Optical Engineering, Bellingham, 2005), pp. 265-278.
24. J. J. Adams, J. A. Jarboe, C. W. Carr, M. D. Feit, R. P. Hackel, J. M. Halpin, J. Honig, L. A. Lane, R. L. Luthi, J. E. Peterson, D. L. Ravizza, F. Ravizza, A. M. Rubenchik, W. D. Sell, J. L. Vickers, T. L. Weiland, T. J. Wennberg, D. A. Willard, and M. F. Yeoman, “Results of sub-nanosecond laser-conditioning of KD2PO4 crystals,” in Laser-Induced Damage in Optical Materials: 2006, G. J. Exarhos, A. H. Guenther, and K. L. Lewis, eds. (2007).
25. K. R. P. Kafka, S. Papernov, and S. G. Demos, “Enhanced laser conditioning using temporally shaped pulses,” Opt. Lett. 43(6), 1239–1242 (2018). [CrossRef]
26. C. W. Carr, J. B. Trenholme, and M. L. Spaeth, “Effect of temporal pulse shape on optical damage,” Appl. Phys. Lett. 90, 041110 (2007). [CrossRef]
27. W. Jian-cheng, S. U. Gen-bo, Z. Guo-zong, L. I. Guo-hui, Z. O. U. Yu-qi, Z. Yua-nan, H. U. Guo-hang, H. Wan-xia, and Z. Xin-xin, “Continuous Filtration System for Rapid Growth and Quality Analysis of KDP Crystals,” Journal of Synthetic Crystals 39, 1–4 (2010).
28. X. Cai, X. Lin, G. Li, J. Lu, Z. Hu, and G. Zheng, “Rapid growth and properties of large-aperture 98%-deuterated DKDP crystals,” High Power Laser Sci. Eng. 7, 03000e03046 (2019). [CrossRef]
29. X. Lü, Y. Peng, W. Wang, Y. Zhao, X. Zhu, and Y. Leng, “High-energy, high-repetition-rate ultraviolet pulses from an efficiency-enhanced, frequency-tripled laser,” High Power Laser Sci. Eng. 9, e38 (2021). [CrossRef]
30. J. J. Adams, J. A. Jarboe, M. D. Feit, and R. P. Hackel, “Comparison between S/1 and R/1 tests and damage density vs. fluence (rho(phi)) results for unconditioned and sub-nanosecond laser-conditioned KD2PO4 crystals,” in Laser-Induced Damage in Optical Materials: 2007, G. J. Exarhos, A. H. Guenther, K. L. Lewis, D. Ristua, M. J. Soileau, and C. J. Stolz, eds. (2008).
31. S. G. Demos, M. Staggs, and H. B. Radousky, “Bulk defect formations in KH2PO4 crystals investigated using fluorescence microscopy,” Phys. Rev. B 67(22), 224102 (2003). [CrossRef]
32. J. X. Huang, Z. Q. Wang, B. Teng, H. Liu, X. X. Zheng, and S. H. Ji, “The effects of deuteration-levels in solution and temperature on the segregation coefficient of the deuterium content in rapid-grown K(DxH1-x)(2)PO4 crystals via Raman spectroscopy,” CrystEngComm 22(21), 3664–3669 (2020). [CrossRef]
33. C. W. Carr, M. D. Feit, M. A. Johnson, and A. M. Rubenchik, “Complex morphology of laser-induced bulk damage in K2H(2-x)DxPO4 crystals,” Appl. Phys. Lett. 89, 131901 (2006). [CrossRef]
34. G.-H. Hu, Y.-A. Zhao, D.-W. Li, and Q.-L. Xiao, “Wavelength Dependence of Laser-Induced Bulk Damage Morphology in KDP Crystal: Determination of the Damage Formation Mechanism,” Chin. Phys. Lett. 29(3), 037801 (2012). [CrossRef]
35. M. D. Feit, A. M. Rubenchik, and J. B. Trenholme, “Simple model of laser damage initiation and conditioning in frequency conversion crystals,” in Laser-Induced Damage in Optical Materials: 2005, G. J. Exarhos, A. H. Guenther, K. L. Lewis, D. Ristau, M. J. Soileau, and C. J. Stolz, eds. (Spie-Int Soc Optical Engineering, Bellingham, 2005).
36. M. M. Chirila, N. Y. Garces, L. E. Halliburton, S. G. Demos, T. A. Land, and H. B. Radousky, “Production and thermal decay of radiation-induced point defects in KD2PO4 crystals,” J. Appl. Phys. 94(10), 6456–6462 (2003). [CrossRef]
37. A. Dyan, M. Pommies, G. Duchateau, F. Enguehard, S. Lallich, B. Bertussi, D. Damiani, H. Piombini, and H. Mathis, “Revisited thermal approach to model Laser-Induced Damage and conditioning process in KH2PO4 and D2xKH2(1-x)PO4 crystals,” in Laser-Induced Damage in Optical Materials: 2006, G. J. Exarhos, A. H. Guenther, and K. L. Lewis, eds. (2007).
38. G. Duchateau, M. D. Feit, and S. G. Demos, “Transient material properties during defect-assisted laser breakdown in deuterated potassium dihydrogen phosphate crystals,” Journal of Applied Physics 115(10), 103506 (2014). [CrossRef]
