The laser

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Valedictory Lecture

by

David Hanna

University of Southampton

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From Big Bang to the LASER:

some historical highlights

Years ago

 Big Bang 13.7±0.2 Gyr

 First stars 12.5 Gyr

 Our sun (solar system) 4.5 Gyr

 First life on earth 3.5 Gyr

 Cambrian explosion (proper vision evolved) 530 Myr

 Homo Sapiens evolved 100 kyr

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Years ago

 Big Bang 13.7±0.2 Gyr

 First stars 12.5 Gyr

 Our sun (solar system) 4.5 Gyr

 First life on earth 3.5 Gyr

 Cambrian explosion (proper vision evolved) 530 Myr

 Homo Sapiens evolved 100 kyr

 Cave painters at work 30 kyr

From Big Bang to the LASER:

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Astronomers & physicists grapple with the nature of light

Rømer 1676 Observing Jupiter’s moons, revealed light to have finite velocity

Young 1801 Measured light wavelength; calculated frequency 

Maxwell 1862 Electromagnetism: LIGHT is an electromagnetic wave

Planck 1900 Birth of quantum theory

Einstein 1905 Special theory of relativity, based on invariance of “c” 1905 Postulated particle of light, of energy h

1916 Introduced the process of stimulated emission

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Astronomers & physicists grapple with the nature of light

Rømer 1676 Observing Jupiter’s moons, revealed light to have finite velocity

Young 1801 Measured light wavelength; calculated frequency 

Maxwell 1862 Electromagnetism: LIGHT is an electromagnetic wave

Planck 1900 Birth of quantum theory

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Speed of light measurement 1676

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Astronomers & physicists grapple with the nature of light

Rømer 1676 Observing Jupiter’s moons, revealed light to have finite velocity

Young 1801 Measured light wavelength; calculated frequency



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On the Theory of Light and Colours Philosophical Transactions of the Royal Society of London

Vol92(1802) 12-48

Double slit experiment 1801

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wavelength

frequency

velocity

c

f





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On the Theory of Light and Colours Philosophical Transactions of the Royal Society of London

Vol92(1802) 12-48

Double slit experiment 1801

Thomas Young (

1773-1829)

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Velocity of light, and the metre

Measure



and f: hence calculate velocity of light

In 1983

c

defined as 299792458 m/s

“...and let’s all go home early”

John Hall

Metre

defined as distance travelled by light in

vacuum in

1

/

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Astronomers & physicists grapple with the nature of light

Maxwell 1862 Electromagnetism: LIGHT is electromagnetic wave

Einstein1905 Special theory of relativity, based on invariance of “c” 1905 Postulated particle of light, of energy h



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James Clerk Maxwell

(1831-1879)

War es ein Gott, der

diese Zeichen schrieb?

(Was it a god who wrote these signs?)

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Astronomers & physicists grapple with the nature of light

Maxwell 1862 Electromagnetism: LIGHT is an electromagnetic wave.

Planck 1900 Birth of quantum theory

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Max Planck

(1858-1947)

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Einstein 1905 Special theory of relativity, based on invariance of “c”

1905 Postulated particle of light, of energy h

Maiman1960 Created first laser light

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Astronomers & physicists grapple with the nature of light

Einstein 1905 Special theory of relativity, based on invariance of “c” 1905 Postulated particle of light, of energy h

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Amplification by stimulated emission

Energy E₂

Photon energy h = E₂ – E₁

Stimulated emission Absorption

Energy E₁

Spontaneous emission

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Nobel prize for physics 1964

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Amplification of an input beam

Amplification of spontaneous emitted light

Amplification plus feedback: oscillation builds up a

directional output -

Laser oscillation

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Taming the laser: the pursuit of perfection

Temporal shaping

Spectral filter to shape spectrum, eg to discriminate against unwanted frequencies

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Figures of merit for light sources

Power Spectral

≡

Brightness _{[Diameter x divergence]}2 _[Spectral

Bandwidth]

Power Brightness ≡

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Brightness of some typical sources

Tungsten lamp, visible light

50W diode bar

1mW laser pointer

1W Ar laser (488nm)

1kW laser @1µm

1MW laser @1µm

30fs, 1mJ @0.8µm

45TW @0.8µm * * * * * * 105 1010

3 x 109

4.5 x 1012

1015

1018

5 x 1022

7 x 1025

W/m2_/sr

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The birth of nonlinear optics

Laser field E is strong enough to modify response of medium

Nonlinear response

Response aE + bE2_{+ cE}3_{+ …}

Peter Alden Franken

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One minute guide to

Optical Parametric Amplification

Second harmonic generation

Sum frequency generation

Parametric generation and AMPLIFICATION

ω₁, ω₂ are amplified in presence of strong pump field at frequency ω₃ Any pair ω₁, ω₂ that add to ω₃ can be amplified

OPTICAL

ω

ω 2ω

ω₁

ω₂ ω3 = ω1 + ω2

ω₂

ω₃ ω1

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Cutting, drilling, welding, scribing, marking chip repair, printing, lithography

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Laser gyros, sensors, pollution monitors, bar-code readers DVDs, displays, entertainment

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Microscopy, surgery, corneal sculpting, optical coherence tomography

Optoelectronics forecast: $1012_{global market by 2015}

The laser:

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The laser:

‘a solution in search of a problem’!

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Optical communications

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Military/defence

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Machine tool control

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Isotope separation

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Surveying, ranging, LIDAR, Doppler speed monitoring

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Security, forensic

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Optical materials and structures

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Laser materials

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Semiconductor laser, quantum wells, wires, dots

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Nonlinear optical materials

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Optical fibres, waveguides

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Bragg gratings for fibre, waveguides, semiconductors

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Photonic bandgap materials, holey fibres

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Metamaterials

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The laser as a scientific tool

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Ultrafast time resolution

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Laser fusion

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Laser particle accelerator

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Gravity wave observatory

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Laser guide star for astronomy

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Optical clocks, frequency standards

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Quantum computing

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Tests of QED, General relativity

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Coherent control

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Atom interferometry

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Short pulse generation with lasers

Pulse of time duration T secs requires a spectral bandwidth of at least 1/_T Hz, hence also carrier frequency of at least 1/_THz

Pulse duration Required bandwidth

10-9_{s, 1ns (nanosecond)}

10-12_{s, 1ps (picosecond)}

10-15_{s 1fs (femtosecond)}

10-18_{s, 1as (attosecond)}

109_{Hz, 1GHz (Gigahertz)}

1012_{Hz, 1THz (Terahertz)}

1015_{Hz, 1PHz (Petahertz)}

1018_{Hz, 1EHz (Exahertz)}

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Electric field of optical pulse

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Manipulation of atoms

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Atom cooling, trapping, guiding

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Bose-Einstein condensation

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Atom interferometers

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Coherent control of atoms

Optical pulses Atom state Atom phase 1 2

|1 + a |2

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Kathleen Puech, Rudiger Paschotta, Paul Suni, Markus Pollnau, Dave Shepherd, David Cotter, Andy Clarkson, Richard Wyatt, Mike Percival, Ralf Koch, Sylvain Girard, Martin O’Connor, Helen Pask, Jose Sais, Michael Yuratich, Joseph Koo, Simon Mussett, Dave Arnold, Barry Luther-Davies, Vikram Rampal, Andy Turner , Richard Wyatt, Leslie Laycock, Pertti Karkkainen, Walter Tuttlebee, Craig Sawyers, Andy Berry, David Hearn, David Pratt, Ian Carr, Marco Pacheco, Ian Alcock, David Pointer, Ken Ure, Andrew Kazer, Leigh Bromley, Ian Perry,

Andy Guy, Michael Ibison, Matthew McCarthy, Colin Mackechnie, Martin Milton,

Tony Neilson, Stuart Butterworth,

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