Control of Single Nanoparticles

1.
“Nanophotonics and Optical Control of
Single Nanoparticles”
(Nano Tweezers)

2. OUTLINE
 Brief History of Optical Tweezers
 Principles of Optical Tweezers
 Optical Trapping Forces
 The Optical Tweezers Set up &
The Experimental Method
 Research Areas and Possible uses

3. Introduction to Optical Tweezers

4. • As science and technology go nano, scientists search for new
tools to manipulate, observe and modify the "building blocks"
of matter at the nanometer scale.
• Recent publication in Nature Nanotechnology in which ICFO
researchers demonstrate for the first time the ability to use
near-field optical tweezers to trap a nano-size object
and manipulate it in the 3 dimensions of space.
• By shining a laser light through a lens, it is possible to focus
light in a
tiny spot, creating an attractive force due to the gradient of
the light intensity of the laser and thus attracting an
object/specimen and maintaining it in the spot/focus.
• While Optical tweezers have changed forever the fields of both
biology and quantum optics, the technique has considerable
limitations, one of which being its inability to directly trap
objects smaller than a few hundreds of nanometers

5. What is…
Optical Tweezers - one of the
techniques, which use a highly focused
beam to control and hold microscopic
particles.

6. History
 Johannes Kepler (1571-1630): noticed comet's tail always
points away from the sun, because of the sun's
radiation pressure.
 James Maxwell (1831-1879): existence of the light pressure
was demonstrated
 P. N. Lebedev (1866-1912): measured the light pressure
 Albert Einstein (1879-1955): confirmed that photons possess
its own momentum
 Arthur Compton (1892-1962:) showed the existence of the
light momentum on his experimental work
Light transfers momentum to matter

7.  In 1970 A. Ashkin proved that light can grab and
release nanometer particles by its momentum, using the
light Quantum Theory.
 In 1986, A. Ashkin proved that he could trap 10nm
diameter dielectric particles only using gradient
force
 In 1987, A. Ashkin showed the damage-free manipulation
on cells using an infrared laser
Arthur Ashkin
History

8. Types of OT
 Single Beam Optical Tweezers
 Dual beam Optical Tweezers
 Holographic Optical Tweezers

9. Principles of OT
 Exert a laser beam to the very small particle, the light will be
reflected or refracted from the surface of the particle. The
momentum of photon, refracted to the particle, will be changed
and by the law of the conservation of the momentum, the force of
the variation of momentum will be exerted to the small particle.
(a) If the particle is to the left, say, of the center of the beam,
it will refract more light from the right to the left, rather than
vice versa.
The net effect is to transfer momentum to the beam in this direction,
so, by Newton’s third law, the particle will experience an equal and
opposite force – back towards the center of the beam. In this
example the particle is a dielectric sphere
(b) Similarly, if the beam is tightly focused it is possible for the particle to
experience a force that pushes back towards the laser beam.
(c) We can also consider an energetic argument: when a polarizable particle
is placed in an electric eld, the net eld is reduced. The energy of thefi fi
system will be a minimum when the particle moves to wherever the eld isfi
highest – which is at the focus. Therefore, potential wells are created by
local maxima in the fields.How optical tweezers work
Optical tweezers: the next generation, Kishan Dholakia,
2002, physics world

10. Conditions of OT
The Ray Optical Regime of Optical
Tweezers Wonhoe Koo, Seoul, 2005
The Electromagnetic Regime of Optical
Tweezers

11. Two Forces
The Electromagnetic Regime of Optical
Tweezers
The Gradient Force

12. Two Forces
The Gradient Force
The Ray Optical Regime of
Optical Tweezers Wonhoe
Koo, Seoul, 2005

13. The Basic OT Set up
A generic optical tweezers diagram with only the
most basic components
The Optical Tweezers, Wikipedia

14. Research
areas Study and manipulate particles such as atoms,
molecules and small dielectric spheres
(in range from µm to nm).
 Force measurements of biological objects in
piconewton range.
 Biological investigations involving cells
 Cutting and ablating biological objects
(Cell fusion and DNA cutting)
 Force measurements of cell structures and DNA
coiling
 Elasticity measurements of DNA

15. Thank you

17. Shedding Light on the Matter
How can matter interact with light?
Three forms of matter-light
interactions play an
important role in how people
see light.
•When light enters a
medium:
• the medium lets all light
pass(Transparent)
• Some light
passes(Translucent)
• or no light pass through.
(Opaque)
Interactions of Light

18. How can matter interact with light?
• Matter that transmits light is transparent.
• Matter that transmits light but scatters it in all directions
is translucent.
• Matter can absorb light. When light enters a material but
does not leave it, the light is absorbed.
• Absorption is the transfer of light energy to matter.
• Opaque materials do not let any light pass through them
because they reflect light, absorb light, or both.
Copyright © Houghton Mifflin Harcourt Publishing Company
Interactions of Light

19. How can matter interact with light?
• Matter can reflect light. Reflection is the bouncing of light
off a surface.
• Nearly everything we can see, we see because light is reflected off
a surface.
Interactions of Light
When light strikes
smooth surface, the
light bounces off at
an angle equal to
the angle at which
it hit the surface,
producing a clear
image.
When light strikes an
uneven surface, the
light is reflected in
many directions. You
see the object but do
not see a reflected
image of yourself.

20. Color Me Impressed!
What determines the color of objects we see?
• When white light strikes an
object, the color of the
object depends on how
the object transmits,
reflects, or absorbs the
colors of light.
• An object that reflects
a certain color of light
appears to be that color.
Interactions of Light

21. What determines the color of objects we see?
• When light is transmitted
through an object, the object
can absorb some colors and
allow other colors to pass
through.
• The color that passes through
a transparent or translucent
object determines the color of
that object.
• Some matter absorbs certain
types of electromagnetic
waves and allows other types
of electromagnetic waves to
pass through.
Interactions of Light

22.  Night vision technology has shaped history.
 Pre 1940’s: Flares and spot lights were used
for operations at night.

23.  Due to the nature of these early night vision
devices (NVD), they gave away tactical
positions.
 Military scientists began to think of ways to
improve night vision to gain a strategic
advantage.

24. A tank fromWorld
War II equipped
with a search light
used for night
combat.

25. Thermal Image
A thermal image (thermogram) is a digital representation of a
scene and a measure of the thermal radiation emitted by the
pictured objects. Thermal images are captured via thermographic
cameras, which are devices capable of sensing this radiation in
the form of infrared light. A thermal image allows us to
remotely sense the temperature of an object or at least
accurately tell its temperature relative to its environment. This
is useful as it allows us to essentially "see" in the dark as
well as perceive the temperatures of many objects
remotely
Infrared Light
Infrared light, or IR, consists of the long wavelengths of light
just beyond our visual perception of nearer red wavelengths in
the visible spectrum. All electromagnetic radiation carries
energy, but infrared light is more readily absorbed by
matter, which increases its kinetic energy, therefore
increasing its temperature. Since all matter is emitting IR
light as a result of blackbody radiation and is a function of
its temperature, being able to accurately sense the IR
radiation can allow us to create a thermal image.

26. Bolometer
In a basic sense, a bolometer is a simple sensor that absorbs
thermal radiation, and changes resistance as a result.
This change in resistance can be electrically measured, and the
incident radiation (which should be a function of the
object's temperature) can be determined. A bolometer is a
large thing, so in this case, the small array of sensors in the
cameras are microbolometers.
So, with an array of bolometers, we've got the basic means of
detecting IR radiation from an object, which, as part of the
thermal radiation as a function of the objects temperature,
means we can begin to depict the thermal scene on our own
terms. Thermal cameras need to be aware of a few properties in
order to work properly. What are the thermal properties of the
thing we are trying to measure? This depends on a few factors:
Absorption, Transmission, Emission, Reflectivity.

27. 27
NIGHT VISION GOGGLE DRIVING OPERATIONS
Anatomy of the Eye
The LENS can change shape to focus on objects
at different distances from the eye.

28. 28
NIGHT VISION GOGGLE DRIVING OPERATIONS
Anatomy of the Eye
The RETINA is the lining at the back of the eye where
the
image is formed. The picture seen by the retina is

29. Night Vision Devices
• A night vision device (NVD), also known as night optical/observation
device (NOD) and night vision goggles (NVG), is an optoelectronic device that
allows images to be produced in levels of light approaching total darkness.
• The image may be a conversion to visible light of both visible light and near-
infrared, while by convention detection of thermal infrared is denoted thermal
imaging.
• The image produced is typically monochrome, e.g. shades of green. The devices
are classified into the following generations
• 1.1.1Generation 0
• 1.1.2Generation 1 (GEN I)
• 1.1.3Generation 2 (GEN II)
• 1.1.4Generation 3 (GEN III)
• 1.1.5Generation 3+ (GEN III OMNI IV - VII)

30. Night Vision Devices
Generation II, III and IV devices use a microchannel plate for
amplification. Photons from a dimly lit source enter the
objective lens (on the left) and strike the photocathode (gray plate).
The photocathode (which is negatively biased) releases electrons which
are accelerated to the higher-voltage microchannel plate (red). Each
electron causes multiple electrons to be released from the microchannel
plate. The electrons are drawn to the higher-voltage phosphor
screen (green). Electrons that strike the phosphor screen cause

31. Why do NVD
devices always
show images in
hues of green?
A) The original designers of NVD
had an obsession with the color.
B)The actual first inventors of
NVD were little green aliens.
C) NVD use green because it
allows for more defined
images.

32. C
The screen was purposefully colored
green due to the scientific fact that the
human eye can differentiate more
shades of green that any other color.

33. Thanks