Study on the thermal stress evolution in large scale KDP crystals during the crystal extraction process

Area of Science:

• Materials Science
• Crystallography
• Solid Mechanics

Background:

• Potassium dihydrogen phosphate (KDP) crystals are crucial for laser applications.
• Crystal extraction can induce thermal stress, leading to cracking.
• Understanding stress evolution during KDP crystal removal is vital for successful manufacturing.

Purpose of the Study:

• To predict temperature and thermal stress evolution in large KDP crystals during extraction.
• To compare the effects of two different crystal extraction methods on internal stress.
• To investigate the influence of crystal size and temperature difference on KDP crystal cracking.

Main Methods:

• Transient numerical calculations were employed.
• Simulations modeled temperature and thermal stress evolution.
• The study considered two distinct crystal extraction processes.

Main Results:

• Highest stress shifts from crystal periphery to internal regions over time for both methods.
• Direct extraction to air results in higher peripheral stress and failure probability.
• Retaining solution leads to higher internal stress but lower overall stress compared to direct extraction.
• Larger crystal size and greater temperature differences exacerbate cracking.

Conclusions:

• Retaining KDP crystal solution for approximately 96 hours post-growth is recommended for successful extraction.
• This method reduces the likelihood of crystal cracking compared to direct air exposure.
• Optimizing the post-crystallization holding period is critical for KDP crystal integrity.