Thermal lens effects in an organic nonlinear crystal pumped by 1.5 um laser

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K04971
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Optical engineering, Photon science
• Research Institution: Chiba University
• Principal Investigator: MIYAMOTO Katsuhiko 千葉大学, 大学院工学研究院, 准教授 (20375158)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: テラヘルツ / 有機非線形光学結晶 / 熱レンズ効果 / 屈折率

Outline of Final Research Achievements

We investigated the local refractive index change i.e., thermal lens effect, in an organic crystal induced by the pump beam during terahertz (THz) wave generation by measuring the focal position change of the probe beam. The measurement system of the thermal lens effect is based on the tunable THz source under difference frequency generation. The change in the focal length of the probe beam incident on the crystal coaxially with the pump beam was measured with and without the pump beam as a function of the incident power. In the case of the DAST crystal, the thermal lens effect was observed only on the a-axis of the crystal regardless of the polarization direction of the pump beam. It is anticipated that results obtained from our measurement technique will enable the development of a non-destructive inspection of the laser damage threshold of an organic nonlinear crystal.

Free Research Field

応用光学

Academic Significance and Societal Importance of the Research Achievements

有機非線形光学結晶は分子間の水素結合からなるため、結晶欠陥・歪みなどが入りやすくレーザー照射耐性が無機結晶に比べ低い。このため、潜在的に有する高い非線形性を十分に発揮できていないのが現状である。プローブ光を用いて結晶内の局所的な屈折率変化を非破壊・非接触で直接観測できる本手法では、屈折率変化の面内分布だけでなく、偏光依存性および時間分解が可能である。熱レンズ効果測定を用いることで、結晶品質を客観的に評価し結晶育成技術の改善にフィードバックすることが期待できる。