Nonlinear optics: Moving from the laboratory to applications
October 8, 2012
Peter Moulton Q-Peak, Inc.
Outline
• A few personal notes
• Harmonic generation
• Optical parametric oscillators
• Highly nonlinear optics
This is not an academic review by any means!
Harvard connection
First brush with nonlinear optics (1965) Physics meets the Beatles
Harvard connection - renewed
Ruby lasers enabled demonstrations of NLO
Pictures of first ruby laser at Hughes
My pursuits in linear optics bore fruit in 1982
Materials technology does matter!
Outline
• A few personal notes
• Harmonic generation
• Optical parametric oscillators
• Highly nonlinear optics
The parade of nonlinear crystals
• KDP (KH2PO4) family (inherited from acoustic transducers)
• Niobates - LiNbO3, KNbO3, Ba2NaNb5O12
• KTP (KTiOPO4) family
• Borates - BBO (β-BaB2O4), LBO (LiB3O5), BiBO (BiB3O6)
• Quasi phase-matched – Periodically poled (PPLN, PPSLT, PPKTP) – Orientation patterned (OP-GaAs)
12
Not always this easy to grow these big crystals
KDP (thanks to Cleveland Crystals, LLNL)
Uses for big crystals
Key to practical laser fusion?
Going Bananas – and then reality hit
16
KTP (and isomorphs)
• Features – High damage threshold – CPM for Nd SHG has large
acceptance angle – Relatively temperature
insensitive – Large apertures available for
high-energy systems – Isomorphs available for
special applications • Bugs
– Induced absorption limits average power in green
– High n2, self focusing – Damage centers (gray
tracking) form in bulk with green generation
– Explodes when absorbing energy too quickly
(KTA)
17
BBO
• Features – Large birefringence, allowing
phase-matching over a wide range
– Moderate nonlinearity – High damage threshold – Good UV transparency – Temperature insensitivity
• Bugs – Large birefringence, leading
to large walkoff and small angular acceptance
– Tendency to form damage centers with UV generation
18
BBO extends operation into the UV
19
Phase-matching angle vs. wavelength
400 600 800 1000 12000
10
20
30
40
50
60
70
80
90
FUNDAMENTAL WAVELENGTH (nm)
INTE
RN
AL
PHA
SE-M
ATC
HIN
G A
NG
LE (d
eg.)
BBO
LBO
KDP
TYPE I SHGd = 0
20
BAWS system uses UV-generating uchip laser
Thanks to NG Component Technologies
Bad things happen in the UV
Coping with bad things
Walk-off in birefringent phase-matching
Theory shows low walk-off focusing is better
Results with BBO 262-nm generation
Low-walkoff 3 W maximum power
High-walkoff 5.3 W maximum power
26
LBO
• Features – Very high damage threshold – Ability to operate with NCPM – Excellent UV transparency – Negligible bulk optical
absorption – No bulk damage ever
observed • Bugs
– Tricky to grow – Funky thermal expansion
makes coating difficult – Not enough birefringence to
generate 4th harmonic
27
Chen (on the right) credited with inventing LBO at Fujian (who is that other guy?)
28
LBO can be temperature tuned into NCPM
29
LBO NCPM SHG conversion approaches 70%
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 100 200 300 400 500 600 700 800
Intensity (MW/cm2)
Effic
ienc
y
Note: Intensity is peak in space and timeAverage spatial intensity is half the value shown
Data pointsTheory for 1.8-cm crystal
LBO-based systems can generate multi-100-W powers
The new MambaTM Green from Coherent Inc. is a frequency doubled, diode-pumped solid-state laser that offers an exceptional combination of high output power, outstanding reliability and low cost of ownership for a wide range of materials processing tasks. The Mamba Green delivers over 325 Watts of output at 532 nm (at 10 kHz), yet its integrated doubling crystal shifter and field replaceable gain modules provide an expected operating lifetime of over 25,000 hours.
Goodbye (and good riddance) to argon-ion lasers
Spectra-Physics Millenia (up to 15 W cw)
Coherent Verdi (up to 18 W cw)
Finally delivers the promise of cw green from 1968
Outline
• A few personal notes
• Harmonic generation
• Optical parametric oscillators
• Highly nonlinear optics
33
Time reversal of interactions is allowed
Nonlinear interaction ω1
ω2
ω3 = ω1 + ω2
Nonlinear interaction ω1
ω2
ω3 = ω1 + ω2
34
BBO OPO widely used in research lasers
Spectra-Physics OPO product
36
KTA OPO tuning curves, 1053-nm pump
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
45 50 55 60 65 70 75 80 85 90
Angle (deg.)
Wav
elen
gth
(um
)
Signal, x-cutIdler, x-cutSignal, y-cutIdler, y-cut
37
OPO resonator designs
pump
signal RING
pump signal
HT pump HR signal
PR signal HR pump
20 mm KTP STANDING-WAVE M1
pump
450 mJ, 10 Hz 41% conversion Limits: M1 damage Pump feedback
TIR prism
4, 10-mm KTP
240 mJ, 30 Hz 34% conversion No feedback No damage at full power
38
Photo and schematic of KTP ring OPO
39
Highest-energy OPO, NCPM KTP
0
100
200
300
400
500 15
71-nm
OPO
Outp
ut
0.2 0.4 0.6 0.8 1 1.2 1064-nm Pump Energy (J)
4.5 W average power
40
Plot of KTP and KTA IR transmission
3000 3200 3400 3600 3800 40000
20
40
60
80
100T = 75% @ 3297nm
T = 23% @ 3297nm
KTA 2cm KTP 2cm
Wavelength (nm)
%T
41
High-average-power eyesafe OPO uses KTA
0 20 40 60 80 100 1200
5
10
15
20
25
30
35
Pump Power (Watts)
Sign
al P
ower
(Wat
ts)
M.S. Webb et al. Opt.Lett. 23, 1161 (1998)
42
Biological standoff detection system used high-power KTA OPO
43
Lithium Niobate
• Features – Large nonlinearity – Large crystal sizes possible
• Bugs – Color centers form with
visible light generation, destroying phase-matching
– Relatively low surface damage threshold
– Surface acts as dust magnet due to pyroelectricity
• Rescued by QPM for OPO
applications
3” diameter stoichiometric crystals
44
Quasi-phase-matched materials operate by periodically changing sign of nonlinearity
J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Pershan, “Interactions between light waves in a nonlinear dielectric,” Phys. Rev. 127, 1918 (1962).
Periodic reversal possible in ferro-electrics
46
Marty Fejer (on the left) led development of PPLN. Who is the other guy?
47
PPLN material (HC Photonics)
Standard Lengths* 10, 20, 30, 40 and 50 + 0.05 mm
Thickness 0.5 / 1.0 mm(+ 0.05 mm) typical
Width* 5 mm (+ 0.05 mm)typical
Single grating period > 4 mm
Multi-grating periods 6.5 ~32 mm
Damage Threshold 300 MW/cm2 (10ns, 1064nm)
48
QPM of PPLN OPO allows mid-IR generation
VIPER system protects aircraft against heat-seeking missiles (MANPADs)
Fundamentals of color displays
• In order to display a full range of colors, electronic displays that project images on a screen must combine red, green and blue light
• Conventional projectors with lamps as light sources take the white light from the lamp and separate out the red, green and blue colors with filters
• Lasers can be used as light sources, and in prior systems three lasers were needed for each color
51
High-power RGB source uses LBO in all nonlinear stages
Pump Laser SHG
1047 nm 523 nm
OPO
SHG
SHG
898 nm
1256 nm
449 nm
628 nm
Blue
Green
Red
Pump LaserPump Laser SHG
1047 nm 523 nm
OPO
SHGSHG
SHGSHG
898 nm
1256 nm
449 nm
628 nm
Blue
Green
Red
A temperature-tuned NCPM LBO OPO is the key element in the system
600700800900
1000110012001300140015001600170018001900
100 110 120 130 140 150 160 170 180
Temperature (C)
Sign
al, i
dler
wav
elen
gth
(nm
)
IdlerSignal
523.5-nm pump
First projection attempts lacked color balance
Successful spin-out
Salem, N.H. -- Laser Light Engines (LLE), a Salem-based developer of laser illumination technology for high-brightness digital projection, announced it has raised $9 million in venture funding, with an additional $6 million anticipated from new investors, bringing the company’s total new funding to $15 million. Founded in 2008, LLE manufactures laser-driven color modules and illumination engines for high-brightness performance projection, signage and lighting applications. The company said the new investment funds will be used to support product rollouts, and strengthen its engineering, sales and manufacturing operations. LLE has now raised $27 million in private funding since its founding. http://www.laserlightengines.com
Outline
• A few personal notes
• Harmonic generation
• Optical parametric oscillators
• Highly nonlinear optics
Kerr-lens modelocking (KLM) provides a fast switch to enable femtosecond generation
AO-MODULATOR
GVD COMPENSATINGPRISMS
Ti:SAPPHIRECRYSTAL
BRF
PUMPAO-MODULATOR
GVD COMPENSATINGPRISMS
GVD COMPENSATINGPRISMS
Ti:SAPPHIRECRYSTAL
Ti:SAPPHIRECRYSTAL
BRF
PUMP
Femtosecond OPOs based on Ti:sapphire
Tunable, high-repetition-rate, femtosecond pulse
generation in the ultraviolet M. Ghotbi, A. Esteban-Martin, and
M. Ebrahim-Zadeh,*
ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Barcelona, Spain
Institucio Catalana de Recerca i Estudis Avancats,
Passeig Lluis Companys 23, Barcelona 08010, Spain *Corresponding author: [email protected]
Counting optical cycles (KLM + SESAM)
Seriously- nonlinear optics (O(20))
Lucent Technologies
R. Windeler J.K Ranka, R. S. Windeler, A. Stenz, Opt. Lett. 25, 25 (Jan. 2000)
Microstructured fiber dispersion zero at ~800 nm pulses do not spread continuum generation via self-phase modulation
-70
-60
-50
-40
-30
Det
ecte
d Po
wer
(dB
m)
1200 1000 800 600 400 Wavelength (nm)
Pre-fiber (Ti:Sapph)
After fiber
• How can we control the absolute frequencies (and hence the group-phase velocities)? Self-referencing
460 480 500 520 540
Fundamental-Second Harmonic
Beats
Repetition Rate
RF P
ower
(10
dB/d
iv)Frequency (MHz)
D. J. Jones et al, Science 288 p 635 28 April 2000
J. Reichert et al., Opt. Comm. 172 pp 59–68 15 Dec 1999
H. Telle et al., Appl. Phys. B 69, 327–332 8 Sept 1999
Locking via Self-ReferencingTechnique
Beat frequency at overlap = δ
Stockholm December 10, 2005
Hansch and Hall win Nobel Prize for Optical Combs
Photonic crystal fiber and microchip laser enable low-cost supercontinuum source
The supercontinuum source shown is built from a NL-1040 PCF pumped by a nanosecond 1064 nm microchip laser.
http://www.crystal-fibre.com/support/Supercontinuum%20-%20General.pdf
microchip laser
Chirped pulse amplification (CPA) avoids NL effects
Courtesy: Wikipedia 1985 (G.Mourou & D.Strikland)
Filaments
This type of propagation is called filamentation or self-guided propagation. filamentation of femtosecond laser pulses was shown to occur over more than 50m in Laboratoire d’Optique Appliquee, (see Fig. 1) and then over several hundreds of meters. Experiments in Spring 2003 at Ecole Polytechnique have revealed an horizontal filamentation over a distance larger than 2 km.
Experiments of vertical propagation suggest even larger filamentation distances.
Mechanism for filament formation in air
Photograph of Ti:sapphire-generated filament
Attosecond pulses, high-harmonic generation
CPA pushes to a Zettawatt (courtesy Mourou)