PH880 Topics in Physics

Modern Optical Imaging (Fall 2010)

KAIST PH880 9/1/2010

PH880 Modern Optical Imaging

• Instructor : YongKeun Park

– Natural Science Bldg. #3305, ykpark@mit.edu

• Website: http://bmokaist.wordpress.com/ph880/– Lecture notes, references, and so on

• Lectures: Mon, Wed, Fri 2-3PM

• Classroom: Natural Science Bldg. #1320 (9/1)

From 9/3, Changeui-gwan (창의관) #409

• Units: 3-0-3

• Office hour: Mon, Wed, Fri, 3-3:30PM, Natural Science Bldg. #3350 (right after the lecture)

KAIST PH880 9/1/2010

Class objective

- Cover the physical principles of modern optical imaging- Physical intuition and underlying mathematical tools

- Systems approach to analyze and design optical imaging system

- Cover the various modern optical microscopes- From bright-field microscopy to super-resolution microscopy

- Application of the optical imaging systems. - Biology: cellular and sub-cellular imaging

- Chemistry: molecular imaging

- Medicine: disease diagnosis

- Engineering: metrology

KAIST PH880 9/1/2010

KAIST PH880 9/1/2010

Drawings of the instruments used by Robert Hooke.

R. Hooke, Micrographia, 1665

Old optical imaging system (1665)

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Recent imaging system (~90s’)

http://www.microscopyu.com

Buccal Epithelial Cells under DIC microscopy

KAIST PH880 9/1/2010

Recent imaging system:Digital holographic microscopy

YK Park et al., Optics Express, 2006YK Park et al, PNAS, 2010

KAIST PH880 9/1/2010

Recent imaging system: super-resolution microscopy

Stephen Hell group, Germany

Course schedule

KAIST PH880 9/1/2010

Period Contents Period Contents

week 1Introduction to optical imaging

Geometric opticsweek 9 Nonlinear microscopy

week 2 Fourier optics week 10 Digital holography

week 3 Fourier opticsBright-field

microscopyweek 11

Optical Coherent Tomography

Photo-acoustic microscopy

week 4 Resolution/Abberations week 12 FRET / SNOM

week 5 Intrinsic contrast microscopy week 13 Super resolution microscopy

week 6 Fluorescent microscopy week 14 Synthetic Aperture / Detectors

week 7 Confocal microscopy week 15 Adaptive Optics in Imaging

week 8Mid-term:

critical review paperweek 16

Final:

presentation on topics in modern

optics

Mathematical tool Conventional Recent Current research topics

Administrative: PH880

• Grade:

– mid-term critical review paper (40 %),

– final presentation (50 %),

– lecture participation (10 %)

KAIST PH880 9/1/2010

Mid-term critical review

• Write a short critical review that involves reading at least 5 papers, discussing the methods, problems, conclusions, in any area on which optical imaging may impinge. (wk 8)

• We will hand out a reading list with some suggestions and examples of papers that you might find useful and interesting, but you are welcome to search for any others as well. (wk 5)

• Maximum length: 7 pages including everything (title page and reference list).

KAIST PH880 9/1/2010

Final presentation

• We will hand out the list of recent papers on the related topic. Each student may choose one from the list (wk 12).

• Write a critical review that involves discussing the methods, problems, conclusions, and suggestions. Maximum length: 5 pages. (final week)

• Each student should be prepared to present an overview of your critical review (using PPT slides) in no more than 20 minutes including Q/A (final week).

KAIST PH880 9/1/2010

Overview of week1

• Wednesday

– Course admin.

– Introduction to optical imaging

– Review: Optics (undergraduate level)

• Friday

– Geometric optics II

KAIST PH880 9/1/2010

Optical imaging

KAIST PH880 9/1/2010

Incident light

Scattering

object

Need optics to “undo” the effect of scattering In free space: focus the light

image

Optical imaging : lens

KAIST PH880 9/1/2010

Point sources(object)

Point images

Each point source from the object plane focuses onto a point image at the image planeNote; image inversion

object plane image plane

Optical system in eye

In DSLR, iris ~ shutter, retina ~ CCD or CMOS panel

Optical system in eye

lensretine

Ideal optical imaging system

KAIST PH880 9/1/2010

OpticalElements

object

• Ideal imaging system:Each point in the object is mapped onto a single point in the image

• In real world, imaging system do not focus perfectly1. Aberration: an imperfection in image formation2. Diffraction limited resolution

image

Aberration

• an imperfection in image formation by an optical system

KAIST PH880 9/1/2010

Perfect focus DefocusAberration

SphericalAberration

ChromaticAberration

Why optical system do not focus perfectly?

• Aberration & Diffraction

• In Geometrical Optics (paraxial approximation), optical system do focus perfectly

• To deal w/ aberration, we need non-paraxial Geometric optics

• To deal w/ diffraction, we need Wave (Fourier) Optics

KAIST PH880 9/1/2010

What is light?

• Light is a form of electromagnetic energy– Heating of illuminated objects, conversion of light to current,

mechanical pressure (“Maxwell force”) etc.

• Light energy is conveyed through particles: “photon”– Ballistic behavior, e.g. shadow

• Light energy is conveyed through “waves”– Interference, diffraction

• Quantum mechanics reconcile two point of view: “wave/particle duality”

KAIST PH880 9/1/2010

KAIST PH880 9/1/2010

Wave properties of light

E

t z

1/

E: Electric field: wavelength (spatial period) [m]k=2/ : wave number (spatial frequency) [rad/m]: temporal frequency [1/s, Hz]=2 : angular frequency [rad/s]

Wave/Particle duality of light

• Photon = light particle

• Energy E = h

h = Planck’s constant = 6.626210-34 Js

= temporal frequency [1/s]

• Dispersion relation : c = c = speed of light = 299,792,458 m/s

= wavelength [m]

* Holds in vacuum only

KAIST PH880 9/1/2010

The light spectrum

KAIST PH880 9/1/2010

Visible spectrum~400 nm ~700 nm

Light in matter: refraction/absorption

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• Speed c = 3x108 m/s

• Absorption coefficient 0

• Speed = c/n

n : refractive index

(index of refraction)

• Absorption coefficient α

Energy decay after distance L :

e-2αL

Light in vacuum Light in matter

* glass fiber has n 1.5, α 0.25 dB/km = 0.0228/km, * Most biological cell & tissue are transparent:

(α is very small, n provides important contrast. )

Refractive index, n

KAIST PH880 9/1/2010

• Note that refractive index is a function of wavelength: ‘dispersion’

Consequence : chromatic aberration

• Air: n slightly higher than 1

(most commonly assumed n 1 for practical purposes)

• Water: n 1.33

• Cell culture medium : n 1.337 (PBS solution at 633 nm)

• Glass : n 1.45-1.75

• Photorefractive crystal, e.g. Lithium niobate n 2.2-2.3

• Solution: depending on the concentration of solute, C

nX = nw + α · C

nX : n of solution (e.g. Hemoglobin)

nw : n of solvent (e.g. water)

α : specific refractive index increment of solute

Overview of week1

• Wednesday– Course admin.

– Introduction to optical imaging

– Review: Optics (undergraduate level)

• Friday– Geometric optics II

Refractive index, Fermat’s principle, Reflection, Refraction, Ray-tracing, lens

KAIST PH880 9/1/2010

Reading list

• R. Barer, Determination of Dry Mass, Thickness, Solid and Water Concentration in Living Cells, Nature 172, 1097 - 1098 (12 December 1953); doi:10.1038/1721097a0

KAIST PH880 9/1/2010