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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.