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3.4 Applications of Optical Tweezers 117
Optical fiber
Spectroscopic data
Q-switch YAG Laser

CCD camera

Dichromatic mirror (DM)
CW YAG Laser
Objective

OH - OH - OH - H
OH - D D H z
D
x
H
y
Electrochemical measurement
Fig. 3.43. Microchemical conversion system for studies of chemical reaction process.
Reprinted from [3.6] with permission by H. Masuhara, Osaka University, Japan

lasers (λ =1, 064 nm) trap and close particles in contact with each other.
Q-switched YAG laser (λ = 350 nm) stimulates the photochemical reaction
between such particles. Such a chemical reaction was studied by a picosecond
time-resolved laser spectroscopy. They expect that such approaches will make
it possible to study the chemical and physical properties of a single fine parti-
cle as a function of its size, shape, surface morphology and to promote highly
selective/efficient material conversion [3.27].

Optics

Micrometer-sized spherical particles can act as optical cavities in air or liquid
[3.28]. Resonant field is formed inside the surface of particles doped with laser
dye such that the light propagates in a circumferential manner due to the
total internal deflection at the interface [3.29]. The optical characteristics of
the microsphere laser oscillation, such as polarization of resonant modes and
interaction between close particles, were studied. Photon tunnelingfrom the
lasingmicrosphere to an object was demonstrated as a marked change of
an emission spectrum dependingon microsphere-to-object distance. Lasing
microspheres have the advantage of high sensitivity due to the intracavity
enhancement of tunnelingloss, i.e., a probe of a scanningnear-field optical
microscopy (SNOM) [3.30]. In addition, an optically trapped gold particle
was demonstrated to be a useful near-field probe for the study of the surface
characteristics beyond the diffraction limit resolution [3.31,3.32].