Biomedical Engineering Reference
In-Depth Information
This microscope has the following advantages, as follows. 1) Since the
spring constant for holding a probe particle is so weak, a sample is rarely da-
maged mechanically. 2) There is no need to regulate the distance between the
probe particle and the sample, because the probe particle touches a sample
surface during scanning. 3) Observation with this microscope is done under
water. It is quite useful for biological applications [55] such as fluorescence in
situ hybridization (FISH) [56]. 4) According to the use of a metallic particle,
light intensity scattered by the particle is expected to be much greater than
that from a dielectric particle.
Experimental Setup.
Figure 1.37 shows the experimental setup of the
NSOM. The laser for optical trapping is a Nd : YLF laser (TFR, Spectra-
Physics, 2.5 W, 1047 nm wavelength). This laser beam goes into microscope
optics and is focused with an oil immersion objective (UPlan Apo, 100
,
1.35 NA, Olympus). DM1 in microscope optics is a dichroic mirror which
reflects the light of the Nd : YLF laser and transmits visible light. Due to this
mirror, almost none of the light from the Nd : YLF laser penetrates to the
upper part of the microscope optics.
The laser for sample illumination is an air-cooled Ar ion laser (Uniphase,
20 mW, 488 nm wavelength). This laser is also incident on the microscope
optics and is focused onto the probe particle. The spot position of the Ar
ion laser corresponds to that of the Nd : YLF laser. Scattered light from the
probe particle is collected with the objective, and an image is formed at
the position of a pinhole and detected with a photomultiplier tube (PMT)
×
Optical
Fiber
PMT
PC
Monitor
Pinhole
Image Processor
Ar ion Laser
Galvano
mirror
BS2
λ
=488nm
BS1
Controller
Quadrant Detector
DM1
Nd:YLF Laser
y
ab
cd
λ
=1047nm
Microscope
Objective
NA=1.35
x
Driver
PZT Controller
PZT XYZ
Fig. 1.37.
The experimental setup of the laser trapping NSOM
