Transcript Atoms, Lasers and Computers Rainer Grobe Intense Laser Physics Theory Unit

Atoms, Lasers and Computers
Rainer Grobe
Intense Laser Physics Theory Unit
Illinois State University
see
a factor 2
Professor George Skadron
Physics Chair
1986 - 1997
Skadron’s physics niche for ISU
challenge:
• specialization (without too narrow expertise)
• top notch research agenda
solution:
Computational Physics
=> unique education for our undergraduate students
Traditional Physics
?
?
theory
?
?
The new problem
Laws of nature are established
but: we can’t solve the equations ....
solution: Computers can calculate numbers
example:
x = 2 -x
=>
x=0.611857....
Modern Physics
simulation
theory
Structure of the laws of nature
know: Y(t=8
00
)
system at 8
goal: Y(t= 9 00)
lim
t  0
00
predict future at 9 00
Y(t  t)  Y(t)
t
rate of change of Y
= F [ Y(t) ]
= function of Y
examples for Y:
position
temperature
field
examples for F:
Newton
Maxwell
Dirac
Continuity of time = unjustified assumption
Has mathematics gone too far by requiring t -> 0
Do we really need the strict limit
∞
Discretization of the laws of nature (∞)
no limits:
=> choose t finite (t = 1 sec)
Y(t+t) = Y(t) + F[Y(t)] t
present
8 00
future
8 00 + 1sec
Y(t)
time
8 00
9 00
repeat the forward step 3600 times
Computers can do it !
Advantages of Computer Experiments
compared to laboratory experiments
• safer
• cheaper
• exactly reproducible
• all ingredients controllable
• simultaneous measurements
• insight into ultrafast mechanisms
most importantly:
• going beyond present technology
Impact of computer experiments
on research areas
nonlinear dynamics and chaos
space-plasma physics
solid state physics
laser science
3 examples of breakthroughs due
to computer simulations
1996 : Adiabatons
2000 : Cycloatoms
2003 : Birth of matter
I. Optical signal transmission
wave = frequency & amplitude
change amplitude: pulse can carry information
Dream:
medium
output
(identical to input)
input message
Reality:
medium
input message
output
(distorted & damped)
Challenge: prevent losses & distortion
input
medium
almost no output
Second beam can protect the original field !
input
medium
output
“control the optical properties of medium”
Computer simulations of adiabatons
before
after
bodyguard
input signal
output signal
• prediction by computer simulation :
1994
• experimental verification (Stanford Univ.) : 1996
Could adiabatons become important?
applications in
•
optical switches
•
wavelength converter non-demolition signal replicator
•
pulse-shape controller
•
long distance transmission
Storage and recall of optical information
storage:
medium in ground state
energy levels
medium in excited state
recall:
Jennifer Csesznegi and RG, Phys. Rev. Lett. 1997
Laboratory experiments are presently viewed as important
1997: Discovery of this effect in computer simulations
1999: Experimental verification at Harvard:
measured speed of light: only 17 m/s (factor of 20 million!)
New York Times (Front page on February 18)
Glossy article in Time Magazine
Appreciation of the value of computer simulations is growing ..
II. Atom in strong laser fields
Laser intensities in W/cm2
• laser pointer:
10–3
• laser welding:
106
• world record:
1019
≈ 1000 lighting bolts
Robert Wagner (Computer Physics Major 1998-2002)
 13 Publications
 14 Conference presentations
 Barry Goldwater Scholarship
 USA All Academic Team
 Leroy Apker Award in 2002
now a graduate student at Princeton
Power and curse of quantum mechanics
i   i c    mc 2  V(r)Y(r, t)  0


 t

P.A.M. Dirac
most accurate description of nature:
example: electron’s mag. moment: experiment: 1.0015965219
Dirac:
1.0015965220
When does an atom decay ? ............. no answer
Where is the electron ?
............. no answer
k I can safely say that nobody understands quantum mecha
Richard Feynma
Difficulties with quantum mechanics
conceptual: provides only probabilities
technical: difficult to solve
Alternative approach
use Newtonian mechanics
approximate quantum wave function by an ensemble of quasiparticles
...does it work
?
Quantum mechanics ≈ Classical ensemble !
wave function
for an atom
electron
cloud
nucleus
ensemble density
for the same atom
Patience is better than brute force
Past belief:
strong laser only
=> fast electrons
=> electron oscillates
magnetic field only
=> electron orbits in circle
Trick: use the resonance
+
magnetic field
=
laser field
very fast electron
Use resonance to accelerate electron
3 108 m/s1
0.8
speed of light
electron’s velocity
80% of c
0.6
108
0.4
m/s
0.8
0.9
1
1.1
1.2
1.3
magnetic field strength
laser field frequency = cyclotron frequency
=> no need for expensive high-power lasers
Computer simulation of a hydrogen atom
in a strong laser and magnetic
1013 W/cm2
field
1010 Gauss
magnetic field strengths:
• earth:
1
• magnet:
102
• neutron star: 1015
Time evolution of a cycloatom
QuickTime™ and a
Apple Motion JPEG Format A decompressor
are needed to see this picture.
Articles from Science Writers about Cycloatoms
Ivars Peterson of
Science News
“Ring around the Proton”
Science News Vol. 157, No.18, 287 (2000)
David Ehrenstein of
Physical Review Focus
“Fast Electrons on the Cheap”
Physical Review Focus 5 (April 6, 2000)
Daniel S. Burgess of
Photonics Spectra
“Physicists Play Ring-Around-the-Atom”
Photonics Spectra 34, 26 (2000)
Herczeg János of
Élet es Tudomány
“Atomi Hulahopp”
Élet Tudomány Vol. 18, May 5 (2000)
Half resonance
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Could cycloatoms become important?
w3
w2
Laser input
wL
wL
w1
cycloatoms generate new light with very high frequencies
Evolution of the electron’s spin
III.
E = mc 2 in space & time resolution
Dream: to simulate how a particle is “born” from pure energy
1928
1932
1940
1973
1989
2001
2003
Dirac equation
Positrons discovered
Progress in interpretation Feynman/Schwinger
Application to quarks
First experiment: conversion of laser -> matter
Correlated wave function formalism
First computer simulations
Questions can now be addressed:
Where is the electron born?
What is its wave function?
What are its coherence properties?
The birth of an electron-positron pair
The birth of an electron-positron pair
_
+
Are e and e born at same location?
electron & positron’s
uncertainty cloud
no simultaneous
occurence
Electron and positron are born “on top of each other”
ISU support
Honors’ program
URG program
College of A&S
Collaborators at ISU
Students
Robert Wagner
Peter Peverly
Shannon Mandel
Allen Lewis
Michael Bell
Tony Piraino
......
PostDocs
Harsha Wanare
Sunish Menon
Piotr Krekora
Faculty
Charles Su
George Rutherford
Michael Marsalli
Hiroshi Matsuoka