Martin Frimmer (mfrimmer@ethz.ch) Photonics Laboratory ......Welcome! 3 Martin Frimmer...

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Welcome!

www.photonics.ethz.ch 1

Martin Frimmer (mfrimmer@ethz.ch)Photonics Laboratory (Prof. Lukas Novotny)HPP, floor M

Welcome!

www.photonics.ethz.ch 3

Martin Frimmer (mfrimmer@ethz.ch)Photonics Laboratory (Prof. Lukas Novotny)HPP M24

This lecture is about learning about (and controlling) the world around us using measurements based on electromagnetic radiation. At hand of examples (e.g. super-resolution microscopy, feedback-cooling of mechanical resonators), we familiarize ourselves with the concepts of measurement imprecision and measurement backaction to explore some fundamental limitations of light-based measurement and control schemes.

This is the first iteration of this course!Suggestions, corrections comments welcome!

Administrative details

• Besides lecture, website is important source of informationwww.photonics.ethz.ch Education EM Precision…

• Read Infosheet on website to find out about grading and components of course:

1. Lecture

2. Homework problems

3. Paper presentations

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What is this lecture about?

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• What do you do to find out what is inside a box?

• In this lecture, we think about “what it means, to look inside the box”.

On the menu today

• Motivation: Why precision measurements?

• Repetition: electromagnetism

• Optical imaging:

• Focusing by a lens

• Angular spectrum

• Paraxial approximation

• Gaussian beams

• The diffraction limit

• Fluorophores and fluorescence microscopy

• Super-resolution microscopy

• Example: STED microscopy

• Example: Localization microscopy

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The Helmholtz equation and plane waves

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Dispersion relation:

Plane waves: Speed of light:

Refractive index:

H

E

k

(E, H, k) are mutually orthogonal for

from

wavelength

period

Phase velocity

follows

from follows

real valued

On the menu today

• Motivation: Why precision measurements?

• Repetition: electromagnetism

• Optical imaging:

• Focusing by a lens

• Angular spectrum

• Paraxial approximation

• Gaussian beams

• The diffraction limit

• Fluorophores and fluorescence microscopy

• Super-resolution microscopy

• Example: STED microscopy

• Example: Localization microscopy

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How does focusing by a lens work?

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x

Intensity

Boundless.com

How does focusing by a lens work?

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x

k

q1 = 0°

I(x) = E(x) E*(x) = ?

Intensity

How does focusing by a lens work?

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x

I(x) = E(x) E*(x) = ?

q1 = 20°

k

Intensity

How does focusing by a lens work?

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x

q1 = ± 20°

k k

I(x) = E(x) E*(x) = ?

Intensity

How does focusing by a lens work?

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x

q1 = ± 45°

kk k

Intensity

How does focusing by a lens work?

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x

q1 = ± 80°

k k

Intensity

How does focusing by a lens work?

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x

q1 = 0°, ±45°

kkk

k

Intensity

How does focusing by a lens work?

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x

q1 = 0°, ±15°, ±30°, ±45°,

±60°, ±75°

Intensity

How does focusing by a lens work?

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x

q1 = 0°, ±15°, ±30°, ±45°,

±60°, ±75°+apodization

Intensity

How does focusing by a lens work?

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Angular spectrum

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MATH :

Angular spectrum

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MATH :

PHYS :

Angular spectrum

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MATH :

PHYS :

Together:

Angular spectrum

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PHYS :

Together:

Paraxial approximation

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mit

Fields propagate predominantly in z-direction !

On the menu today

• Motivation: Why precision measurements?

• Repetition: electromagnetism

• Optical imaging:

• Focusing by a lens

• Angular spectrum

• Paraxial approximation

• Gaussian beams

• The diffraction limit

• Fluorophores and fluorescence microscopy

• Super-resolution microscopy

• Example: STED microscopy

• Example: Localization microscopy

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Gaussian beams

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Gaussian Beams

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Waist Radius

Wavefront Radius

Phase Correction

Rayleigh Range

Gaussian Beams

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A better description of focused fields

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Far-field

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?

Method of stationary phase :

Far-field

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Angular spectrum in terms of far-field

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For kz ~ k: Fourier Optics !

From method of stationary phase:

Boundless.com

Back to the lens

• We can calculate the field near a focus if we just know the far-field

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So what does a lens do?

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Ray Continuity

(energy conservation)

Angular spectrum representation

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Change coordinates

Coordinates on reference sphereCoordinates in focal region NA

Strongly focused Gaussian beam

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Strongly focused Gaussian beam

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Weakly focused beam

• Assume strongly overfilled back-aperture

• Assume small NA

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Focal plane (z=0):

Not Gaussian !

:

Why is this a jinc?

On the menu today

• Motivation: Why precision measurements?

• Repetition: electromagnetism

• Optical imaging:

• Focusing by a lens

• Angular spectrum

• Paraxial approximation

• Gaussian beams

• The diffraction limit

• Fluorophores and fluorescence microscopy

• Super-resolution microscopy

• Example: STED microscopy

• Example: Localization microscopy

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Imaging of point sources: Single molecule detection

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Fluorescent molecules – Jablonski diagram

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Single molecule detection

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fluorescence rate ~ excitation rate

x

y

contrast ~ | m .E(x,y;zo)| 2

Single molecule detection

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What does the image of a point-source look like

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Source Plane Image Plane

Point-spread function

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Classical resolution limit

www.photonics.ethz.ch 63E. Abbe, Arch. Mikrosk. Anat. 9, 413 (1873).

Source Plane Image Plane

4 4

Abbe’s Resolution Limit

www.photonics.ethz.ch 64E. Abbe, Arch. Mikrosk. Anat. 9, 413 (1873).

On the menu today

• Motivation: Why precision measurements?

• Repetition: electromagnetism

• Optical imaging:

• Focusing by a lens

• Angular spectrum

• Paraxial approximation

• Gaussian beams

• The diffraction limit

• Fluorophores and fluorescence microscopy

• Super-resolution microscopy

• Example: STED microscopy

• Example: Localization microscopy

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