description of a pulse train
DESCRIPTION
To the change in phase between successive pulses. corresponds a frequency::. t RT. j e. Electric field. Time. Description of a pulse train. The “ideal” mode-locked laser emits a train of identical pulses:. The change in phase from pulse to pulse is a measurable quantity, - PowerPoint PPT PresentationTRANSCRIPT
Description of a pulse train
The “ideal” mode-locked laser emits a train of identical pulses:
To the change in phase between successive pulses
corresponds a frequency::
The change in phase from pulse to pulse is a measurable quantity,independent of the duration of the individual pulse in the train.
Ele
ctri
c fi
eld
Time
eRT
Ele
ctri
c fi
eld
Time
Ele
ctri
c fi
eld
FrequencyRT
avf0
eRT
p
RT
Description of a pulse train
p = e(i + 1) - e(i )
A train of functions
//
Ele
ctri
c fi
eld
Time//
RT
Coherence
e
Ele
ctri
c fi
eld
Frequency
Coherence
RT
b
av
f0RT
p
p = e(i + 1) - e(i )
Description of a pulse train
A train of pulses
Ele
ctri
c fi
eld
Frequency
Coherence
RT
b
av
f0RT
p
p = e(i + 1) - e(i )
Description of a pulse train
The mode comb
p
700 800 900
100
200 (a)
Rep
. Rat
e -
101
884
000
Hz
Wavelength [nm]
Mode locked laser comb:
fixed teeth spacing. D
counter
Fixed number
Spectro.
Unequally spaced teeth
Tuned cw laser: the mode spacingvaries with frequency
2L
n()
/c
D
counter
Mode-locking = Laser Orthodontist
Two burning questions:
As a pulse circulates in the cavity,
does it evolve towards a steady state?Which mechanism makes the
unequally spaced cavity modes
equidistant?
Evolution of a single pulse in an ``ideal'' cavity
How unequally spaced modes
lead to a perfect frequency comb
Evolution of a single pulse in an ``ideal'' cavity
Dispersion
Kerr effect
Kerr-induced chirp
How unequally spaced modeslead to a perfect frequency comb
Phase delayGroup delay
Cavity modes: not equally spaced because nav = nav()
Unequally spaced modes, is contradictory to the fact that comb teeth are equally spaced.
where
where
dispersion
A cavity with ONLY Kerr modulation generates the pulse train:
F.T.
Two burning questions:
As a pulse circulates in the cavity,
does it evolve towards a steady state?
Which mechanism makes theunequally spaced cavity modes
equidistant?
Evolution of a single pulse in an ``ideal'' cavityHow unequally spaced modes
lead to a perfect frequency comb
SAME
CONDITION
The choice of the optimum metrology method for a given problem
The right tool for a given measurement: An overview
The pulse train
TOOLS: Simple analog oscilloscope and frequency doubling crystal.
The right tool for a given measurement
Electronic Spectrum analyzer
Both fundamental and second harmonic: a straight line.
Spectrometer
What to look for?
No sideband and higher harmonics
Continuous spectrum, central wavelength
THE PULSE TRAIN
An overview
The right tool for a given measurement
THE PULSE TRAIN
An overview
Both fundamental and second harmonic: a straight line.
Electronic Spectrum analyzer
The right tool for a given measurement
THE PULSE TRAIN
An overview
What we should not see:
Modulation of the train on a s scale
(Shows as a sideband on spectrumanalyzer on a 100 KHz scale)
Q-switched-mode-locked train
TOOLS: Scanning autocorrelator, Intensity, interferometric, spatially encoded Spider
The right tool for a given measurement
THE PULSE OF A TRAIN
Do you want to tune the laser to get the shortest pulse?
Tuning a laser oscillator Tuning a high power system
An overview
Single pulse characterization at high repetiton rate: SPIDER