The Quantum Cascade Laser Revolution and its Future FEDERICO … · 2013-10-11 · Ultraviolet...
Transcript of The Quantum Cascade Laser Revolution and its Future FEDERICO … · 2013-10-11 · Ultraviolet...
FEDERICO CAPASSO
School of Engineering and Applied Sciences
Harvard University
http://www.seas.harvard.edu/capasso
The Quantum Cascade Laser Revolution and its
Future
Recent reviews:
Federico Capasso ,Journal of Optical Engineering 49, 111102 (2010)
Robert Curl, F. Capasso e et al. Chemical Physics Letters 487, 1 (2010)
Spectral coverage of lasers
100 200 300 400 500 600 700 800 900 1,000 3,000 30,000
Ultraviolet Visible Near-infrared Mid-infrared terahertz
HeNe 633 nm
Ruby 694 nm
Nd:YAG 1064 nm
XeF 351 nm
XeCl 308 nm
KrF 248 nm
ArF 193 nm
Ti:sapphire 700-1000 nm
Ar-ion 364-514 nm
Diode
Dye
CO2
10.6 µm
QCLs
Er:YAG
2.94 µm
QCLs: First Lasers to provide broad wavelength
coverage for a largely underdeveloped spectral
region with major commercial opportunities
Diode lasers
~ 3 - 0.3 m
Quantum Cascade
Lasers (QCLs)
(=3-300m)
Electronics
up to ~1 THz (=300m)
First demonstration: 1994
J. Faist, F. Capasso, D.L. Sivco, C. Sirtori, A.L.
Hutchinson, A.Y. Cho,
Science 264, 553, (1994)
Molecular Fingerprint Region
Microwaves THz Mid-IR Near
-IR UV
Mid-IR: Molecular Fingerprint Region
Mid-Infrared:
Every molecule has a unique
absorption fingerprint
→ chemical sensing with high
sensitivity and selectivity
Applications
• Industrial process control and Pharma
- In line process control; Compliance testing of tablet,
capsules, powders
-Quality control of chemical processes from reagents to
products
• Homeland security & DOD: standoff detection of
explosives
and hazardous gases
• Medical: breath analysis, tissue imaging
• Environment / Energy: pollution monitoring,
• atmospheric chemistry
QCLs have become unique tools for the real time, highly sensitive selective and
non-invasive detection of chemicals as well as for high-power cw applications
ELIMINATION OF BAND-GAP SLAVERY: USES STATE OF THE ART
InP BASED and GaAs BASED EPIGROWTH PLATFORMS FOR PHOTONICS AND
ELECTRONICS
Quantum design: laser properties (wavelength, gain spectrum, lifetimes
population inversion) designed from wavefunctions, energy levels, matrix elements
Higher performance (high cw power at RT) can be obtained with a four well 2-phonon design
In0.53Ga0.47As/Al0.48In0.52As/InP GaAs/AlxGa1-xAs
QCLs: quantum design and epilayer growth
What makes the QC Laser special?
Wavelength agility: layer thicknesses determines wavelength; huge
λ design range; ultrabroadband band lasing and tuning
Unipolar nature & cascading which reuses electrons: high optical power
Intersubband transition; broadening insensitive to temperature:
temperature insensitivity of laser threshold (high T0: hundreds of K)
Ultra-fast carrier lifetime: no relaxation oscillations
Negligible spontaneous emission rate compared to (lifetime)-1
linewidth limit smaller than given by standard Schawlow-Townes
formula
Design of giant nonlinear susceptibilities in active region: coherent
phenomena at room temperature and new nonlinear optical sources
Quantum Cascade Laser: compact, cryogenic-free and bright laser source in the Mid-IR
2011: Commercialization in full swing
High performance mid-ir QCL using same high volume InP technology
platform of telecom photonics (lasers, etc.) based on MOVPE epigrowth
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Homeland Security and DOD
- Remote detection of multiple chem/bio agents and aerosols.
- Detection of explosives.
- Target illuminators and beacons.
- Infrared countermeasures.
- Directional infrared optical wireless.
Industrial Process Control
- In-line process control of water based chemical reactions.
- Monitoring complex systems in real-time and continuously.
- In-vivo algae monitoring of yield and quality.
- Detection of unwanted biological species in drinking water.
- Pollution monitoring.
- Microfluidics monitoring.
Healthcare Diagnostics
- Of single or multiple small molecules in real-time for healthcare.
- In-line compliance testing of tablets.
- In-line compliance testing of tablet, capsules, etc, through
polymeric blister packaging.
Law Enforcement
- Providing early detection and analysis for forensic services.
Energy
- Monitoring and controlling energy conversion in the
transportation industry.
Mid-infrared Market Needs & Opportunities
High Power CW Room Temperature Operation
= 4.6 µm
A. Lyakh, C. Pflügl, et al., APL 92, 111110 (2008)
Strain compensation for large barrier heights (0.7-0.8 eV) : low carrier leakage; Diamond sub-mount.
www.pranalytica.com
QCL in conjunction with FTIR spectrometers
were used for
- spectroscopy through water
- reflection measurements
- standoff detection
Future Improvements:
• development of high power broadband QCLs
• software/data treatment to improve signal to noise
• better collection optics
• take advantage of polarized emission
from QCL to increase background discrimination
QCLs in conjunction with FTIR: a good marriage
Broadband devices and with high brightness
3-to-4 orders of magnitude larger than Globars
C. Pfleugl et al. CLEO 2010 Technical Digest
Infrared
camera
PC
controller
Electronics
Laser
head
QC Laser head: QCL, wavelength 8.3-8.9 m
100mW average power
Camera: FLIR A40, 30 frames per second
320x240 microbolometer array
Wood
Plastic
Glass
Cardboard
Metal
Illuminated objects
placed 100ft. away
from laser head
Standoff-detection
Distributed feedback laser : Single mode selection by 1st
order grating placed above active region: λ/2n) = Λ
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Melting of Arctic Icecaps and Greenland: less energy reflected from sun
Methane and Carbon Dioxide Release from Permafrost Melting
•
Global Warming and Climate change:
driven by powerful feedbacks
ATMOSPHERIC (Troposphere & Stratosphere) TRACE GAS
MEASUREMENTS WITH QCLs
TRACE
GAS
cm-1 std dev 1s
ppb
76 m path
LoD
ppb
100 s
NH3 967 0.2 0.06
C2H4 960 1 0.5
O3 1050 1.5 0.6
CH4 1270 1 0.4
N2O 1270 0.4 0.2
H2O2 1267 3 1
SO2 1370 1 0.5
NO2 1600 0.2 0.1
HONO 1700 0.6 0.3
HNO3 1723 0.6 0.3
HCHO 1765 0.3 0.15
HCOOH 1765 0.3 0.15
NO 1900 0.6 0.3
OCS 2071 0.06 0.03
CO 2190 0.4 0.2
N2O 2240 0.2 0.1
13CO2/ 12CO2 2311 0.5 ‰ 0.1 ‰
LIGHTWEIGHT
MULTIPASS
CELL (76m)
LASER 1
CH4
1270.785
N2O
1271.078
CO
2179.772
LASER 2
ABSORPTION SPECTRUM
DUAL-LASER INSTRUMENT DESIGN
Pole-to-Pole Observations (HIPPO)
of Carbon Cycle and Greenhouse Gases
Gulf Stream V Aircraft
QCLs for CO2, CO, CH4, N2O
LATITUDE AND ALTITUDE
PROFILES OF TRACERS FOR
GLOBAL CIRCULATION MODELS
PRECISION: (MIXING RATIO)
CO2 30 ppb (340 ppm)
CO 0.2 ppb (80 ppb)
CH4 0.8 ppb (1800 ppb)
N2O 0.1 ppb (320 ppb)
PI: STEVEN WOFSY, HARVARD U.
Fre
e
tro
po
sp
her
e
Lo
wer
str
ato
sp
here
ALTITUDE PROFILES
Stratospheric
intrusion
CO CH4 N2O CO2
Ozone – measured at Beijing Olympics 2008
Ozone
High of 90 – 100 ppb
Low of < 1 ppb
US EPA 8 hour average standard
= 75 ppb
Start of Olympics
Quantum Cascade Laser Open Path
System – “QCLOPS”
Ozone, ammonia, CO2, water vapor
External cavity
QC laser
TE-cooled
detector
Telescope
75m roundtrip
C. Gmachl, Princeton; Zifa Wang; Chinese Acad. Sci. Daylight Solutions Inc.
Exhaled human breath contains ~ 400 different trace gas species, mostly at ultra
low concentration levels. Many of these gases can serve as biomarkers for the
identification and monitoring of various types of human diseases or wellness
states.
Broadband external cavity quantum cascade laser Jerome Faist Group, ETH
Broadband QCLs design by combining dissimilar active regions
Continuous wave: 2 active regions,
201cm-1 tuning (8.0m – 9.6m)
135 mW average Power
Pulsed operation: 5 active regions,
432 cm-1 tuning (7.5m – 11.4m)
1 W peak power
Grating coupled external cavity
High Performance QCL Lab-On-A-Chip
20 cm
Emission spectrum of laser array
Comparison with FTIR spectrometer
• Much higher S/N due to laser rather than
thermal source: remote trace gas detection
• Higher spectral resolution due laser linewidth
• Fast electronic tuning
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Isopropanol, Methanol, Acetone
QCL array: points
Conventional FTIR: solid line
Applications: broad band spectroscopy and sensing
• Fast spectral tuning <<1ms
• Spectral gaps between two adjacent lasers can be
covered by current tuning
• Efficient and rugged spectral been combining demonstrated: longed
distance measurement of gases performed
Highly collimated QCL using plasmonics
SEM image of a fabricated device (=8.06 m) Measured far-field mode profile
FWHM divergence angles:
=2.7o (reduction by a factor of ~30)
||=3.7o (reduction by a factor of ~10)
Apertur
e size
w1
w2
(m2)
grating
period
(m)
groove
width w
(m)
groov
e
depth
d
(m)
radius of
the first
groove r1
(m)
2.1
1.9 7.8 0.6 1.0 6.0
Large design potential still far to be exhausted
Wide range of chemical sensing applications and increasing
importance of high power applications
High cw power efficiency of QCLs > 30 % ( Max so far 25% by Razeghi
group ) and high power ~ 10 W
Higher performance at short wavelength ( down to 3 microns) and
high performance (power and temperature in THz gap)
QCL at telecom wavelengths? High temperature (T0 = 1000), high
power QCL using Nitrides; chirp free QCLs
Mode-locked / pulsed shaped QCL and mid-ir frequency combs will
open new frontiers in molecular spectroscopy and coherent control
Increased functionality using plasmonics and metamaterials
THE FUTURE