nano-tera poster 2014 third prize mixsel
TRANSCRIPT
Optical
Frequency
Microwave Output
Frequency comb:
Allows connection
between optical and
microwave frequencies
1 mW
10 mW
100 mW
1 W
10 W
aver
age
outp
ut p
ower
100 fs 1 ps 10 ps 100 ps
pulse duration
QW-VECSEL with SESAM QD-VECSEL with SESAM MIXSEL
Ultrafast vertical external cavity surface-emitting laser (VECSEL)!A. S. Mayer, M. Mangold, C. A. Zaugg, S. M. Link, M. Golling, B. W. Tilma, and U. Keller!!ETH Zurich, Institute for Quantum Electronics, Ultrafast Laser Physics
MIXSEL2 RTD 2012
VECSEL: potential compact frequency comb source with
gigahertz repetition rate
Phase shift by saturation !(Kramers-Kronig)!
saturation + positive GDD!➠ quasi-solitons [1]
40302010
0-10-20ph
ase
chan
ge (m
rad)
-4 -2 0 2 4time (ps)
pulse power (a.u.) gain _ = 3 sesam _ = 2 total
experimentally verified in picosecond regime [2]
[1] ! R. Paschotta, R Häring, A Garnache, S Hoogland, A.C Tropper, U Keller, Appl. Phys. B 75 (2002), 445 ! [2] ! M. Hoffmann, O.D. Sieber, D.J.H.C. Maas, V.J. Wittwer, M.Golling, T. Südmeyer and U.Keller, Opt Express 18 (2010), 10143
Ultrafast VECSELs
Motivation
distributed Bragg reflectors for lasing/pump wavelength
active region QWs or QDs
AR section
laser
pump
heat
spr
eade
r
heat
spr
eade
r
pump
output coupler
SESAM
gain
chi
p
Pulse Formation Mechanism
frequency
high freplow!frep
➠ easier to access to individual lines!
➠ higher power per mode!
➠ increased S/N ratio
Requirements!• Broad spectrum!• Fast measurement speed!• Spectral stability!• Mechanical compactness
SESAM:passive loss-modulation
100.0
99.8
99.6
99.4
99.2
99.0
refle
ctiv
ity (%
)
1 10 100 1'000 10'000pulse fluence (µJ/cm2)
ΔRns
ΔR
3.2
3.0
2.8
2.6
2.4
2.2
2.0
-3 -2 -1 0 1 2 3
gain
loss
pulse
Current Status Conclusion & Outlook
compact self-referenceable frequency comb from a
VECSEL
low noise Sub-200-fs pulses combined with high average power
Requirements!• Compact system!• Gigahertz repetition
rates
Multiphoton microscopy:!➠ high penetration depth!➠ high sensitivity!➠ flexibility
(fluorescence plus second harmonic or third harmonic image)Requirements!
• Pulsed IR-source!• Cheap (compared to currently used Ti:Sapphire systems)!
Spectroscopy Metrology Applications
Frequency Combs
Biomedical Imaging
• Optical clock!• Precise frequency
calibration
• Gas spectroscopy!• Process monitoring
and control
Requirements for self-referenceable frequency comb!• Low noise!• Sub-200-fs pulses combined with
high average power
Sub-300 femtosecond QW-VECSEL!➠ 273-fs-pulses at 605 mW of average
output power in a 1.8 GHz-cavity!!
wavelength filter
saturation noise
losses gain SESAM gain GDD
output coupler
[5] O. D. Sieber, V. J. Wittwer, M. Mangold, M. Hoffmann, M. Golling, T. Südmeyer, U. Keller, Optics! Express 19 (2011), 3538, 2011
Chip Design GoalsExperimental Results
First Watt-level femtosecond QD-VECSEL [3]!!➠ 784-fs-pulses with >1 W output power in a
5.4 GHz V-cavity
First CEO-frequency detection of a SESAM-modelocked VECSEL [4]!!➠ amplified and recompressed 240-fs
pulses from a 100-mW VECSEL[3] M. Hoffmann et. al., Optics Express (2011) vol. 19, 8108-8116!![4] C.A. Zaugg et. al., submitted to 6th EPS-QEOD Europhoton Conference
Theoretical Investigations & Simulations
• Iterative application of cavity elements on the pulse !
• Macroscopic measurable parameters as input parameters
correct prediction of output power and pulse duration!
+!design guidelines
high gain saturation fluences for short pulse
generation and high output power
high small signal gain for
high power operation
low saturation fluences of SESAM for short pulse generation!
low and slightly positive GDD for
femtosecond pulses
saturation fluence gain GDD saturation fluence
MIXSEL!!Modelocked Integrated External-Cavity Surface Emitting Laser
VECSEL Chip Structure
Cavity Design
• Distributed Bragg reflector (AlAs/GaAs)-pairs grown on GaAs for laser reflection!
• Active region: Laser light amplification in quantum wells (QW) or quantum dots (QD)!
• Antireflection-coating: Minimizing losses and tuning group delay dispersion (GDD)
• V- or Z-shape cavity!• Pumping under 45°!• SESAM: SEmiconductor Saturable Absorber
Mirror to obtain self-starting pulsed operation
1:1 mode-locking!(spot size on SESAM
= spot size on VECSEL)
VECSEL: compact & cheap pulsed laser source in the IR
spectral range
Dynamic gain saturation!Losses decrease faster than gain!➠ net gain window
VECSELSESAM
optical frequencies
RF beat note
Integration of the absorber
SESAMVECSEL
Cavity Design Goals
-100
-80
-60
-40
-20
int.
(dB
c)
1.51.00.50.0 frequency (GHz)
RBW 100 kHz
fCEO 2fCEO 1
frep=1.75 GHz
-80
-60
-40
-20
0
int.
(dB
c)
1600140012001000800600 wavelength (nm)
680
nm
1360
nm
signal background
RBW 5 nm