Biophysical Society Thematic Meeting - June 28-July 1, 2015

New Biological Frontiers Illuminated by Molecular Sensors and Actuators

Poster Abstracts

22-POS Board 22 Femtosecond Laser Pulses Induced Thermal Lensing Effect in H 2 O via One-Photon Absorption Yi-Ci Li 1 , Yu-Ting Kuo 1 , Po-Yuan Huang 1 , Cheng-I Lee 2 , Tai-Huei Wei 1 . 1 National Chung Cheng University, Chiayi, Taiwan, 2 National Chung Cheng University, Chiayi, Taiwan. Water is essential to the living systems, and the biological importance of water has been recognized for its anomalous chemical and physical properties. Research of photothermoacoustic (PTA) wave in water has attracted much attention in recent years. Also, the field of photoacoustic imaging, cancerous lesion detection, drug delivery, and cell permeabilization has developed rapidly. However, theoretical explanations of the PTA wave generation and propagation mechanism vary widely. Using the Z -scan technique with 820 nm 18 fs-laser pulse trains with train-width and train-to- train separation longer than its thermal diffusivity constant, we investigated PTA wave induced in water. We observed the thermal lensing effect and explained the heat generation by relaxation of the excited molecular motions. The molecular motions, such as vibration and libration, can be excited either by an ultrashort laser pulse via single- or multi-photon process. By comparing the peak and valley separation in the Z -scan results, we realized that water molecules gain excess energy from an 820 nm 18 fs-laser pulse via one-photon excitation associated with the 3 rd -order overtone of molecular vibration. This work gives us a relatively simple and sensitive method for investigating nonlinear optical and thermal properties of water and water-rich samples. Therefore, it has great potential to be applied to research in wide range of biological systems.

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