Download Program Overview Erich Ippen

Advanced Technologies for
Optical Frequency Control and Optical Clocks
Yoel Fink
Thomas Greytak
Erich Ippen
Franz Kaertner
Daniel Kleppner
Leslie Kolodziejski
Jeffrey Shapiro
Franco Wong
Massachusetts Institute of Technology
Research Laboratory of Electronics
Cambridge, MA 02139
Department of Electrical Engineering and Computer Science
Department of Materials Science and Engineering
Department of Physics
<[email protected]>
MURI - Technology for Optical Frequency Control and Optical Clocks
Outline
Few-cycle laser development
• Ti:sapphire, Cr:forsterite, Cr:YAG
• Phase sensitive nonlinear optics
• Attosecond-precision laser synchronization
Optical frequency metrology with ultracold hydrogen
• Hydrogen spectroscopy and frequency referencing
• Locking of femtosecond laser comb to single frequency cw laser
Nonlinear optical techniques for comb technology
• Efficient SHG and DFG with chirped-grating PPLN
• 3-to-1 self phase-locked optical frequency divider
• DFG for comb locking to methane-stabilized HeNe laser
Ultra-broadband mirrors and saturable absorbers for few-cycle lasers
• Novel wide-area GaAlAs oxidized mirrors
• Saturable Bragg reflectors for few-cycle lasers
Cylindrical photonic bandgap fibers
• Novel microstructured fiber for nonlinear optics
• Broadband dispersion characteristics of bandgap fibers
Ultra-low-jitter modelocked diode laser
• Locking to visible wavelength reference
MURI - Technology for Optical Frequency Control and Optical Clocks
5-fs Ti:sapphire Laser
•double-chirped mirrors
•enhanced SPM
•octave-spanning spectrum
•dispersion-managed modelocking
MURI - Technology for Optical Frequency Control and Optical Clocks
Chirped and Double-Chirped Mirrors
λ
TiO2 / SiO2
Bragg-Mirror:
B - Layers
4
SiO2 Substrate
Chirped Mirror:
Air
Bragg-Wavelengthλ
SiO2 Substrate
B
Chirped
λ1
Negative
Dispersion:
λ2 λ2 > λ1
--> R. Szipöcs & F. Krausz (Opt. Lett. 19, 201-203, 1994) Computer Optimization
Double-Chirped Mirror: Bragg-Wavelength and Coupling Chirped
d h = λB /4
SiO2 Substrate
ARCoating
Air
“Impedance” - Matching
MURI - Technology for Optical Frequency Control and Optical Clocks
DCM-Pairs Covering One Octave
Designed
Measured
80
400
0
20
0
80
400
200
60
0
40
-400
20
-600
600 800 1000 1200 1400
WAVELENGTH, NM
0
-200
-400
600
-600
800 1000 1200 1400
WAVELENGTH, NM
Fabricated by Tschudi Group, Darmstadt
MURI - Technology for Optical Frequency Control and Optical Clocks
2
-200
2
40
600
GDD, FS
60
GDD, FS
200
100
REFLECTIVITY (%)
600
REFLECTIVITY (%)
100
5-fs Pulse Characterization
IA C
• Nonlinear autocorrelation
• Spectrum
• Recovered amplitude and phase
0
8
1.0
10
6
0.8
10
0.6
10
-1
-2
4
-3
10
0.4
2
0
c)
-10
0
10
20
TIM E DELAY , FS
FWHM 5 fs
-40
-20
0
20
TIME , FS
30
0.2
S P EC TR UM , a.u.
0.0
600
800
1000 1200
b)
W AV ELE NGTH, NM
P H A SE , R A D IA N
-20
PO W ER , a.u.
a)
40
-4
10
-5
10
0
-
4
-
8
-12
d)
600
800
1000 1200
W AV ELE NGTH, NM
1400
MURI - Technology for Optical Frequency Control and Optical Clocks
Pulse-to-Pulse Phase Slip in a Modelocked Laser
VGROUP ≠ VPHASE
∆φ
gain
Modelocked
laser
2nGL/c
MURI - Technology for Optical Frequency Control and Optical Clocks
RF spectral power density [dB]
Phase-Dependent 2nd Harmonic
0
• rf tones reveal dφ/dt
-20
-40
-60
-80
-100
0
10
20
30
40
RF Frequency [MHz]
50
60
70
MURI - Technology for Optical Frequency Control and Optical Clocks
Stopping the Optical Phase Slip
Trf
mTopt = Trf
The optical frequency is locked to an exact multiple of the rf rep rate !
MURI - Technology for Optical Frequency Control and Optical Clocks
Frequency Locking of Laser Modes
•Phase slip in the frequency domain
cavity
modes
c
2ngL
f1
Locking an octave by SHG:
dφ
δ=
dt
laser
modes
δ = 0 ⇒ f1 =
2f1 = f2 = f1 +
nc
2ngL
f2
mc
mc
⇒ f1 =
2ngL
2ngL
MURI - Technology for Optical Frequency Control and Optical Clocks
Second Harmonic Generation
with Octave-Spanning Spectrum
eiφ
Fundamental
ωo
e2iφ
2nd Harmonic
2ωo
=> Interference between fundamental and 2nd harmonic
MURI - Technology for Optical Frequency Control and Optical Clocks
Continuum Generation with Microstructured Fiber
Power (arb. units)
10
10
10
0
-2
-4
Input
Output
10
-6
400
600
800
1000
1200
1400
Wavelength (nm)
Strong guiding shifts the zero-dispersion
wavelength to the near visible
Spectrum resulting when 80fs pulses
from a Ti:sapphire oscillator are focused
into a holey fiber
J. Ranka et al.
MURI - Technology for Optical Frequency Control and Optical Clocks
1600
• All solid state
• 1.3 µm wavelengths
DCM
OC
DCM
X
Spectral Intensity (norm.)
14 fs Cr:forsterite Laser
M
1
0
1.2
1.4
Wavelength (µm)
1.6
-40
-20
0
20
Delay Time (fs)
40
DCM
L
λ /2
P
Faraday rotator
Nd :YAG
Recent result: SBR stabilized
Interfer. Autocorrelation (norm.)
Autocorrelator
DCM
8
4
0
Chuboda et.al.
MURI - Technology for Optical Frequency Control and Optical Clocks
20-fs Cr4+:YAG Laser
Nd:YVO4
Laser – 1064nm
f = 10 cm
DCM
DCM
2-cm Cr4+:YAG
SBR
OC
DCM
SBR Reflectivity
20 fs FWHM
Wavelength (µm)
MURI - Technology for Optical Frequency Control and Optical Clocks
Overlapping Femtosecond Laser Spectra
Ti:Sapphire, Cr:Forsterite and Cr:YAG
MURI - Technology for Optical Frequency Control and Optical Clocks
A Compact Prismless Ti:sapphire Laser
Octave-spanning spectrum
BaF2
2mm Ti:Al2O3
OC 1
φ = 10ο
L = 20 cm
PUMP
BaF2 - wedges
OC 2
Base Length = 30cm for 82 MHz Laser
Future:
• Even more compact
• Scaling to higher repetition rates
• >500 MHz, ring laser
MURI - Technology for Optical Frequency Control and Optical Clocks
Overlapping Femtosecond Laser Spectra
0
Cr:forsterite
Spectral Power [log]
-10
-20
• Stabilized Cr:forsterite
laser
30 dB
-30
-40
• Laser synchronization
300 asec timing-jitter
Ti:sapphire
• Opportunities:
extended frequency
comb: 600–1600 nm
-50
-60
600
• Compact, prismless
octave spanning
Ti:sapphire laser
and/or
800
1000 1200 1400
Wavelength [nm]
1600
single-cycle pulse
generation
MURI - Technology for Optical Frequency Control and Optical Clocks
Balanced Cross-Correlation for Laser Synchronization
∆t
Cr:fo
-GD/2
Ti:sa
SFG
+
-
The residual out-of-loop timing jitter
measured from 10mHz to 2.3 MHz
is 300 as (a tenth of an optical cycle)
Output spectrum: 650-1450nm
3mm
GD
Fused
Silica
SFG
Cross-Correlation Amplitude
Rep.-Rate
Control
(1/496nm = 1/833nm+1/1225nm).
Time [fs]
1.0
-100
0
100
0.8
0.6
Timing jitter 0.30 fs (2.3MHz BW)
0.4
0.2
0.0
0
20
40
Time [s]
60
MURI - Technology for Optical Frequency Control and Optical Clocks
80
100
Optical Frequency Metrology
with Ultracold Hydrogen
OVERALL GOAL
To pursue ultraprecise spectroscopy of ultracold atomic hydrogen for:
SCIENCE
• Resolve discrepancies in the theory of quantum electrodynamics
• Better values for fundamental constants
• Test theories of atomic interactions and atomic structure
TECHNOLOGY
• Explore the possibilities for an atomic hydrogen optical clock
• Develop and apply techniques for measuring the frequencies of optical transitions
• Stimulate the development and application of optical frequency combs
IMMEDIATE GOAL
Measure absolute frequencies of transitions such as 2S →10S (2-photon, 730 nm)
using atomic hydrogen as an optical frequency standard
MURI - Technology for Optical Frequency Control and Optical Clocks
Spectroscopy with a Hydrogen Optical Clock
Lock to 1S-2S (243 nm)
486 nm
x2
Cold Hydrogen
Excite 2S-10S
Lock
x2
972 nm
764 nm
• Excite 1S→2S transition (known to about 1 part
in 1014.)
• Lock 486 nm laser to 1S→2S
• Excite two-photon transition such as 2S→10S
• Measure excitation frequencies with an optical
frequency comb, referenced to the 486 nm laser,
i.e. referenced to hydrogen
MURI - Technology for Optical Frequency Control and Optical Clocks
Nonlinear Optical Techniques for Comb Technology
Ultra-broadband SHG with zero group velocity mismatch
•
70 nm bandwidth for 1580 nm → 790 nm in PPKTP
Difference-frequency generation of 3.39 µm
•
•
locking Ti:sapphire laser comb to CH-stabilized HeNe laser
collaboration between MIT and JILA
3-to-1 frequency divider
•
•
self-phase-locked optical parametric oscillator with cascaded nonlinear
interactions in PPLN
provides phase-locked markers at 532, 798, and 1596 nm
MURI - Technology for Optical Frequency Control and Optical Clocks
Difference Frequency Generation of 3.39 µm
Servo to lock comb spacing to He-Ne
Ti:S fs pulses
Ti:S spectrum
667 nm
PPLN
difference-frequency
generator
830 nm
cw 3.39 µm output
Phase-locked
}
CH-stabilized
He-Ne
4
@ 3.39 µm
N pairs of modes
yield N2 enhancement
N~15,000
MURI - Technology for Optical Frequency Control and Optical Clocks
Self-Phase-Locked OPO Yields
3:2:1 Frequency Markers
PZT
Signal 798 nm
Pump
PPLN
532 nm
Signal 2ω
Idler 1596 nm
OPO
grating
SHG
grating
2ω
2ω
Pump 3ω
Self-phase locking
(∆ω=0)
ω
MURI - Technology for Optical Frequency Control and Optical Clocks
Ultra-Broadband Saturable Absorber Mirrors
GaAs/AlxOy Mirror
GOALS
• High index-contrast oxidized mirrors
for broadband low dispersion
• In-based absorber optimized for
wavelength – integrated on mirror
• Large area for low power density
delaminated
interface
delaminated
interface
500 µm
AlxOy
• Stable, durable structures
GaAs substrate
PROGRESS
• Integrated broadband SBRs for
Cr:YAG and Cr:forsterite lasers
• Dramatic improvement in layer
stability with AlGaAs/AlxOy structures
• Wide area oxidization
(>500µm diameter)
GaAs
AlGaAs/AlxOy Mirror
GaAs/InGaAs
Al0.3Ga0.7As
AlxOy
500µm
GaAs substrate
MURI - Technology for Optical Frequency Control and Optical Clocks
Issues Affecting the Distributed Bragg Reflector
Oxidation of AlGaAs Layers
R946, 5 hr, 415 C
Oxidized 11/13/2002
GaAs/InGaAs
R946, 5 hr, 415 C
Oxidized 11/13/2002
AlxOy
Al0.3Ga0.7As
GaAs substrate
99µm from mesa edge
13µm from mesa edge
• Edges of mesa less oxidized than at center
• Mirror bandwidth a function of position
MURI - Technology for Optical Frequency Control and Optical Clocks
Issues Affecting Saturable Absorber
5hrs
Sensitivity to
Oxidation
Time
8hrs
~230 µm
420C
435C
Sensitivity to
Oxidation
Temperature
Center = ~3mm from wafer edge
Center = ~11.4mm from wafer edge
Center = ~18.4mm from wafer edge
Sensitivity to
Growth
Temperature
MURI - Technology for Optical Frequency Control and Optical Clocks
OmniGuide Mirror Fibers
primary gap centered around 1.5 µm
MURI - Technology for Optical Frequency Control and Optical Clocks
Bandgap Fiber with and without Defect
Regular OmniGuide structure
100µm
Modified (defect) structure
1µm
MURI - Technology for Optical Frequency Control and Optical Clocks
Mirror-guide Dispersion Characteristics
Fiber with cavity mode
Bandgap fiber
20
LH
15
Dispersion D (ps/nm-km)
Dispersion D (ps/nm-km)
20
10
Metallic
5
0
-5
-10
-15
-20
1.2
15
1.55 µm
LH
10
5
Metallic
ZD
0
-5
-10
-15
1.4
1.6
1.8
2
Vacuum wavelength (µm)
2.2
-20
1.2
1.4
1.6
1.8
Vacuum wavelength (µm)
MURI - Technology for Optical Frequency Control and Optical Clocks
2
2.2
Modelocked External External Cavity Diode Laser
• 500 µm gain section
• 50 µm saturable absorber section
• λ = 1547nm , f = 9.35 GHz
• BPF = 0.7 nm : τ = 6.7 ps
• BPF = 5 nm : τ = 3 ps
VSA
Poseidon
SBO
OSC
I gain
5-nm BPF
MIRROR
R = 99.9%
SELFOC
LENS
OUTPUT
NEC external cavity MLLD
MURI - Technology for Optical Frequency Control and Optical Clocks
Residual Phase Noise Measurement
• Vector signal analyzer for low frequency offsets (1-10 MHz)
• RF spectrum analyzer for high frequency offsets (10 MHz – 4.5 GHz)
VECTOR SIGNAL ANALYZER
OSC AMP 3-dB
AMP
CH1
MLLD
DELAY
CH2
RF ANALYZER
(RF analyzer after mixer has higher sensitivity than for direct detection.)
MURI - Technology for Optical Frequency Control and Optical Clocks
Single-Sideband Phase Noise - Results
• Hybrid MLLD, 9GHz, 6.7 ps, Poseiden SBO
• Vector signal analyzer (0 – 10 MHz)
• RF spectum analyzer (10 MHz – 4.5 GHz)
-80
Vector Signal Analyzer Data
L(f) dBc/Hz
-90
Spectrum Analyzer Data
-100
-110
-120
-130
-140
-150
Vector Signal
Analyzer
Noise Floor
-160
10
100
1k
Spectrum Analyzer Noise Floor
10k 100k
1M
10M 100M 1G
Offset Frequency (Hz)
Integrated timing jitter from 10 Hz to 4.5 GHz = 86 fs
1kHz – 10MHz : 40 fs
154 fs including all noise spurs
SBO jitter = 5.6 fs (10 Hz to 10 MHz)
MURI - Technology for Optical Frequency Control and Optical Clocks
Synchronization of Modelocked Diode Laser
to Visible Standard
MIT-JILA collaboration
D. J. Jones et al. Opt. Lett. 2003
MURI - Technology for Optical Frequency Control and Optical Clocks
Timing Jitter Spectral Density of Stabilized MLLD
20 fs jitter (1Hz – 10 MHz)
MIT-JILA collaboration
D. J. Jones et al. Opt. Lett. 2003
MURI - Technology for Optical Frequency Control and Optical Clocks
Outline
Few-cycle laser development
• Ti:sapphire, Cr:forsterite, Cr:YAG
• Phase sensitive nonlinear optics
• Attosecond-precision laser synchronization
Optical frequency metrology with ultracold hydrogen
• Hydrogen spectroscopy and frequency referencing
• Locking of femtosecond laser comb to single frequency cw laser
Nonlinear optical techniques for comb technology
• Efficient SHG and DFG with chirped-grating PPLN
• 3-to-1 self phase-locked optical frequency divider
• DFG for comb locking to methane-stabilized HeNe laser
Ultra-broadband mirrors and saturable absorbers for few-cycle lasers
• Novel wide-area GaAlAs oxidized mirrors
• Saturable Bragg reflectors for few-cycle lasers
Cylindrical photonic bandgap fibers
• Novel microstructured fiber for nonlinear optics
• Broadband dispersion characteristics of bandgap fibers
Ultra-low-jitter modelocked diode laser
• Locking to visible wavelength reference
MURI - Technology for Optical Frequency Control and Optical Clocks