In situ and real-time monitoring of process parameters during growth of KDP crystal, an important ferroic material

Abstract

This study presents imaging results obtained by applying different optical diagnostics for monitoring the growth of potassium dihydrogen phosphate (KDP) crystal, an important ferroic material. Laser shadowgraphy was deployed for mapping free convection phenomena during the growth of KDP crystal in different geometries. Shadowgraphy results were used to compute the strength of convection and establish a relationship between the growth rate and the crystal quality. Mach–Zehnder interferometer with novel design features was fabricated and used for online measurement of concentration and its gradient during free as well as forced convection modes of growth. The 2-D nature of results obtained using the above techniques was extended to 3-D by implementing the technique of computerized tomography. Michelson interferometer was used for imaging screw dislocation mediated spiral growth mechanism on the pyramidal habit face of KDP crystal. In summary, a variety of diagnostics have been developed that enable in situ and real-time monitoring of the process of crystal growth.

Keywords:

• crystal growth
• KDP
• optical diagnostics
• convection
• concentration
• growth rate

Acknowledgements

The author expresses his reverences to Dr. V.K. Wadhawan for the encouragement and advice received from him for the past several years, particularly during the doctoral research. Sincere gratitude is also due to Prof. K. Muralidhar for his deep involvement in this research.