Determination of ultra-short laser induced damage threshold of KH2PO4 crystal: Numerical calculation and experimental verification

Abstract

Rapid growth and ultra-precision machining of large-size KDP (KH2PO4) crystals with high laser damage resistance are tough challenges in the development of large laser systems. It is of high interest and practical significance to have theoretical models for scientists and manufacturers to determine the laser-induced damage threshold (LIDT) of actually prepared KDP optics. Here, we numerically and experimentally investigate the laser-induced damage on KDP crystals in ultra-short pulse laser regime. On basis of the rate equation for free electron generation, a model dedicated to predicting the LIDT is developed by considering the synergistic effect of photoionization, impact ionization and decay of electrons. Laser damage tests are performed to measure the single-pulse LIDT with several testing protocols. The testing results combined with previously reported experimental data agree well with those calculated by the model. By taking the light intensification into consideration, the model is successfully applied to quantitatively evaluate the effect of surface flaws inevitably introduced in the preparation processes on the laser damage resistance of KDP crystals. This work can not only contribute to further understanding of the laser damage mechanisms of optical materials, but also provide available models for evaluating the laser damage resistance of exquisitely prepared optical components used in high power laser systems.

Ultrafast modification of band structure of wide-band-gap solids by ultrashort pulses of laser-driven electron oscillations

“…This conclusion is evident from the Eqs. (14) and (15). Second, reduction of the effective masses favors reduction of the adiabatic parameter and, therefore, low-effectivemass crystals are more favorable for observation of the reported effects.…”

“…The zero-order terms of the square bracket of Eqs. (14) and (15) correspond to the initial parabolic energy bands homogeneously shifted by the amount of ponderomotive energy evaluated under the monochromatic approximation. The 1/α, 1/α 2 , and 1/α 3 terms of the square bracket describe the effects produced beyond the monochromatic approximation.…”

“…Ultrafast laser interaction with electron sub-system of non-metal solids has been under intensive studies for several decades . The strong interest to that field results from the fundamental fact: the laser-electron interaction and energy deposition into the electron sub-system substantially contribute to all high-intensity ultrafast laser interactions with wide-band-gap crystals, e.g., laser ablation [1][2][3][4][5][6][7][8], laser-induced damage [7][8][9][10][11][12][13][14][15], excitation of transient optical response [16][17][18], direct writing of nanostructures [19,20], and ultrafast nonlinear propagation [21][22][23][24]. A recent development of petawatt (PW) laser systems launched another wave of research activity in this field [25].…”

“…It implies singlefrequency cosine variations of electric field at constant amplitude that is in obvious contradiction with realistic time variations of electric field of a laser pulse. The usual way to overcome this issue is to replace the constant electric-field amplitude with the slowly varying amplitude of a pulse envelope [1,2,4,5,[7][8][9][10][11][12][14][15][16][17][18][19][20][21][22][23][24]. Although this approach raises significant concerns, e.g., when the monochromatic Keldysh formula is applied to laser pulses containing 2-25 cycles [22,[60][61][62], no analysis has been done so far to determine a range of laser parameters where such modification of the monochromatic approximation is valid.…”

Nonlinear Optical and Laser Damage Properties of KDP Crystal with Trace Impurities in Bulk

“…Potassium dihydrogen phosphate (KDP) crystal is an optical material with excellent nonlinear optical properties that has being widely used for frequency conversion and optical switching applications in large‐aperture laser systems such as ICF facilities . Under intense laser irradiation especially at 351 nm, laser‐induced damage in KDP bulk occurred far below the expected intrinsic break‐down limits calculated from the band structure of perfect crystals, which has been a long‐standing issue and deeply influences the lifetime of laser devices. Bulk defects in KDP are considered as majority factors that can absorb the input laser energy, subsequently induce inhomogeneous distribution of temperature field and stress field, and finally initiate laser damage of in bulk of KDP crystal .…”