US Patent 6,297,066 | US Patent pending
External Cavity Quantum
Cascade Laser System
Product Preview - Quantum Cascade Lasers in Littrow
Configuration
Description:
Quantum Cascade Lasers (QCL) are designed for spectroscopy in the MIR
spectral range. The tuning behavior of such semiconductor lasers is often far
from ideal for many applications in high-resolution spectroscopy. To overcome
these drawbacks, Sacher Lasertechnik is developing an External Cavity Quantum
Cascade Laser System in Littrow configuration.
System
Layout:
Operating a QCL measuring system requires several
technologies which will be reviewed briefly at this page:
1.) The laser
driver requires pulsed operation
with injection current values of 5A .. 10A with pulse length of 10nm ..
100ns and a repetition rate of 100kHz.
2.) The laser
head should ensure a low temperature operation of typically 250K for
operating QCL devices. Future improvement of the QCL lasers might overcome
this feature.
3.) The external cavity needs to
be designed for QCL devices. This incluses technology steps like developing the
antireflection coating for QCL lasers as well as the design of the external
cavity itself.
QCL Laser
Driver:
Sacher
Lasertechnik developed a pulsed laser driver for QCL laser devices. Key features
are operation current up to 5A, pulse duration of 5ns .. 100ns, repetition rate
of typically 10MHz. 
QCL Laser Head:
Sacher
Lasertechnik devloped a laser head for QCL lasers which includes a cooling stage
which allows to operate the laser at temperatures down to 250K. Furthermore, the
laser pulser is integrated within the laser head for best modulation performance
of the QCL laser devices.
External Cavity QCL:
Sacher
Lasertechnik developed an excellent antireflection coating for QC Lasers. As
seen in the above figure by the comparison of the black trace with the red
trace, there is a significant change in the threshold current of the QC Laser
due to the antireflection coating. With external cavity the threshold is reduced
due to the feedback of the external cavity as it is seen by the green curve.
Changes of the grating angle of the external cavity setup allows
frequency tuning with QC lasers.
Application Example -
MIR Absorption Spectroscopy:
The fundamental optical
transitions of most molecules are located in the Mid Infra Red (MIR) spectral
range. Typical ocillations strength of the fundamental optical transitions are
more than a factor of 1000 stronger than their harmonic which are located in the
Near Infra Red (NIR) spectral range. Major benefit of the higher value of
oscillation strength is a drastical increased detection sensitivity of optical
sensors. Publications on QCLs report on sensitivites in the ppb regime. With the
large tuning range of the external cavity, the QCL external cavity is a
working horse for this kind of applications.
Availability:
Sacher
Lasertechnik is currently preparing the product release of the External Cavity
Quantum Cascade Laser (ECQCL) system. The product will be available in early
2006. We are searching for cooperation partners for a product evaluation. Please
contact us well in advance with your application.
Acknowledgement:
We
gratefully acknowledge financial support by the BMBF with contract
FK13N8020.
