ScientificTechnical Oral Presentations

1
Femtosecond Pulse Generator using looped
time-lens compression
James van Howe, Jennifer Lee and Chris Xu School
of Applied and Engineering Physics Cornell
University, Ithaca, NY 14853
CLEO, May 11, 2007
2
Motivation
-To reduce the complexity of current femtosecond
pulse generation
-To add flexibility to femtosecond pulse
generation in pulse width, rep. rate, center
wavelength tuning
3
Turn-key Source for a Biologist
Pump
TiSapph
OPO
lt 200 fs, Pulse energy gt 10 nJ limited tunable
rep rate
2.5 m
plug and play femtosecond source
lt 500 fs, Pulse energy 1-10 nJ
Variable tuning of rep rate, pulse width and
center wavelength
4
Why discount fiber lasers?

• 5 mW average power
• 0.1 nJ pulse energy
• 1550, 1040, 780 nm
• 300 fs pulse width

IMRA Femtolite
Needs CPA for amplification to useful energies
Minimal flexibility fixed duty cycle, fixed
wavelength
5
Space-time Duality Lenses
Space
Diffraction
Spatial Lens
kx
Time
t
PM
Time-lens
Dispersion
w
6
Phase Modulators as a Time-lens
7
Stacking many lenses

Time-lens

N time-lenses

Switch 1
Input
w
Time-lens
Switch 2
output

To dispersive device for compression
N loops (N-1) effective lenses
w
8
Messy Details


Pulse Carver
CW DFB
Pulse Picker
MZ
MZ
EDFA

Pattern Generator
EDWA
Input -9.0 dBm
EDWA
BPF
Switch 1
time-lens
Switch 2

BPF
Output -16.0 dBm
Loop Loss 16 dB
9
Time-lens loop Setup
16 in.
10
Loop performance
9 loops, 8 passes through time-lens
1/3150 pulses or 3 MHz rep. rate
No Phase Modulation
With Phase Modulation
-30
-40
Measured
BW0.12 nm
Calculated
-50
-40
BW20 nm
-60
-50
80p radians
Relative Power (dB)
-70
-60
Measured
Calculated
-80
-70
-80
-90
1551.44
1551.64
1551.84
1552.04
1552.24
1540
1545
1550
1555
1560
1565
Wavelength (nm)
Wavelength (nm)
11
Bandwidth Flexibility
-30
-40
-50
-60
Relative Power (dB)
-70
6 trips, 12.1 nm
2 trips, 2.3 nm
7 trips, 14.7 nm
3 trips, 4.6 nm
-80
4 trips, 7.1 nm
8 trips, 17.3 nm
5 trips, 10 nm
9 trips, 19.8 nm
-90
1540
1545
1550
1555
1560
1565
Wavelength (nm)
12
Amplification and Compression
Temporal Loop Output
Compressor
G2
Scope Trace
M2
Loop Output
FWHM 24 ps.
G1
Relative Intensity
C2

M3
D 1.6 ps/nm
EDFA
0
-100
50
100
-50
Time (ps)
To Autocorrelator
Amplified Loop Output
-10
-30
Amplified Output 28 mW Amount in signal 11.3
mW or 3.5 nJ pulses
-50
Relative Power (dB)
Before Amp
-70
After Amp
-90
1540
1545
1550
1555
1560
1565
Wavelength (nm)
13
Compression
Experimental
Calculated
1.0
0.8
0.6
697 fs
600 fs
0.4
516 fs deconvolved
444 fs deconvolved
0.2
0
Normalized Signal
8
6
4
2
0
-15
-10
-5
0
5
10
15
-15
-10
-5
0
5
10
15
Delay (ps)
14
Coarse Repetition Rate Tuning
Real-time Oscilloscope Trace
1
3 trips
0.8
9 trips
9.54MHz
0.6
Relative Intensity
0.4
3.18 MHz
0.2
0
-200
-150
-100
-50
0
50
100
150
200
Time (ns)
In our system, pulse width increases for N lt 9
System flexibility increases for smaller loop
length
15
Fine Repetition Rate Tuning
1
3 trips
9 trips
0.9
3.672 KHz (0.039)
0.8
236 Hz (0.007)
Fraction of Original Bandwidth
0.7
0.6
0.5
-8 -6 -4 -2 0 2 4
6 8
x10-4
Fractional Frequency Detuning from Resonance
Bandwidth degrades from pulses walking off the
center of the time-lens each trip
Superb stability to environmental perturbations
thermo-optical effects change optical length of
loop by only 0.001 per degree Celsius
16
Future Directions

• Amplify pulses to larger power (gt 30 nJ)
• Demonstrate SHG and use pulses for imaging
• Demonstrate super-continuum generation
• Run different phase shapes on PMs in the loop for
  correction, and arbitrary waveform
  generation/pulse shaping

17
Acknowledgments
Chris Xu Cornell University Jennifer
Lee Cornell University
Recent Paper J. van Howe, J.H. Lee and C. Xu,
Opt. Lett. 32 1408 (2007).
Funding through NSF, Grant DBI-0352434
Contact James van Howe, jwv9_at_cornell.edu
http//xugroup.ccmr.cornell.edu/