Optics and Photonics

Selim Jochim together with Dr. K. SimeonidisMPI für Kernphysik und

Uni HeidelbergEmail: selim.jochim@mpi-hd.mpg.de

k.simeonidis@mpi-hd.mpg.deWebsite for this lecture:

www.lithium6.de teaching

What will you learn in this course?

• How to use advanced photonics instruments and technology in the laboratory

• Learn to develop your own ideas on how to make use of photonics for (precision) experiments

• Knowlegde that is widely needed in many labs in Heidelberg:– Biomedical research– Laser spectroscopy– High-power “ultrafast” lasers for atomic physics– Laser cooling and trapping, (quantum) manipulation of

atoms, molecules or ions

Motivation

• We make (increasingly) heavy use of photonics in our daily life. Two interesting examples:

• Green laser pointers emit bright light at 532 nm: How are they made? make use of almost anything you will learn in this course!!

• DVD reader/writer ( resolution of a microscope for a few €!!)

Contents

Preliminary list:

• 11.4. Geometric optics, rays (Fermat’s principle)

• 18.4. No class

• 25.4. Wave optics, gaussian beams (paraxial Helmholtz eq.)

• 2.5. Polarization optics, optical coatings, wave guides, …

• 9.5. Atom-photon interaction

• 16.5. Lasers: Light amplification

• 23.5. Laser oscillation, optical resonators

Contents II

• 30.5. More lasers, solid state lasers, dye lasers, etc.

• 6.6. Pulsed lasers: Q-switching, mode locking, extremely short pulses

• 13.6. Semiconductor photonics: detectors, LEDs, Lasers

• 20.6. Fourier optics, holography

• 27.6. Nonlinear optics concepts

• 4.7. Nonlinear optics applications: Frequency doubling, mixing ..

• 11.7. Advanced applications: Frequency comb, optical synthesizer ...

• 18.7. Lab tour(s)

Recommended literature

• Saleh, Teich: Fundamentals of Photonics

• Kneubühl, Sigrist: Laser

• Davis: Lasers and Electro-Optics: Fundamentals and Engineering

• Demtröder: Laserspektroskopie

• Hecht, Optics (Especially for the first few lectures)

1. Geometric (ray) optics

• Light propagates as rays with “speed of light”, c in vacuum

• In a medium, the light is slowed down by the refractive index n

• In an inhomogeneous system, propagation is governed by Fermat’s principle:

“Minimize” optical path length: ( )d 0B

A

n s r

Fermat’s principle

Phenomenologically:

• Hero of Alexandria (ca. 70 – 10 A.D.): Light always takes the shortest path when reflected from a surface:

Refraction

1 2

2 1

sin sin

n n

A

B

Interfaces between dielectrics …

• n2>n1 …

• Total internal reflection ….

critical angle:

2

1

arcsin( )C

n

n

Where total internal reflection is used

• Prisms, e.g. binoculars, camera viewfinder

• Optical fibers:

Parabolic mirror

Parallel beams are focused onto a single spot:

Car headlight!

Spherical mirror, paraxial rays

Paraxial rays: Assume that all beams propagate “close” to optical axis. In most cases, this means that sin ≈ tan ≈ Rays are focused toF=R/2

Imaging with spherical mirrors

1 2

1 1 1 1

2z z R f

Thin lenses

1 2

1 1 1( 1)( )n

f R R

Paraxial imaging

1 2

1 1 1

z z f 2

2 11

zy y

z

Magnification

Matrix formalism for parax. rays

• Use it to describe a complex optical system with a single (2,2)-matrix

• Define state of a ray by a 2-comp. vector:

valid if

Example matrices

• Free space propagation

• Refraction at a surface

Optical system ….

When the paraxial approx. fails …

Focussing of a laser beam:

Minimize non-paraxial distortions:

Plano-convex lens, also “best form lens”

Spherical aberration …

• Can we make all parallel rays incident on a lens end up in a single spot??

Aspheric lens?

• Optical path length should be the same for all angles ….

Aspheric lenses

• All kinds of quality grades available

• Molded, plastic material

 

Precision machined …

 ASPHERIC LIMITS

    STANDARD

HIGH PRECISION

Diameter (mm)   15-120 15-120

Length (mm)   10.5-85 10.5-85

Width (mm)   10.5-85 10.5-85

Dimensional Tolerances (µm)

  25 5

Center Thickness Tolerance (µm)

  100 35

Wedge Tolerance (µm)

  75 25

Surface Quality   60-40 10-5

Radius Limits (mm)   LRC Limited

LRC Limited

Concave   >30.0 >30.0

Convex   >5.0 >5.0

Radius Tolerance (%)

  0.1 0.05

Total SAG (mm)   <25 <25

Aspheric Surface Accuracy (wave)

 

  1/4 1/10