1. Applications of Quantum Cascade Lasers
† † †‡ †
Sumeet Kumar ⃰, Lyubomir Stoychev ⃰, Roberta Ramponi and Andrea Vacchi .
†
National Institute of Nuclear Physics, INFN, Padriciano 99, Trieste, Italy.
* International Centre of Theoretical Physics (ICTP), Strada Costiera 11, 34151 Trieste, Italy.
‡
Department of Physics, Polytechnic of Milan, Italy.
Contact email: sumeet.kumar@ts.infn.it
Abstract
Quantum Cascade Lasers (QCL) can be employed as sensing platform based on optical
absorption with the principle of probing the vibrational frequencies of targeted molecules
(near/mid-infrared range). Using this technique the unambiguous signature of the fluid
investigated can be detected with high sensitivity for gases and liquids, low price and low power
consumption.
The main applications of the QCL, thanks to its characteristics of being a powerful light source
in the mid-infrared range, can be perceived as optical sensing in the gas phase viz. Human
breath analysis and detection of the helicobacter pylori with isotopic ratio measurements in
exhaled CO2. In particular INFN has instrumentation setup at disposal (see figure 1) into the
detection of various gases like for e.g. CH4 (Sensitivity at: 7.30 - 8.06 µm; Resolution of 0.8
ppb), N2O (Sensitivity at: 7.80 ± 0.2 µm; Resolution of 0.8 ppb), TNT vapor (7.4 µm: Resolution
of 0.1 ppb) etc. Quite interesting are the direct impact of these detections into environmental
effects like global warming (CH4, N2O) and explosive materials detections respectively.
The detection of various gas vapors can be employed with INFN’s experience into conducting
R&D using: Distributed Feed-Back (DFB) in pulsed and continuous wave modes with emission
λ’s of 6.78, 9.18 µm having a tunablity of 0.11nm/V and 0.35nm/K together with Fabry-Perot
(FP) QCL (λ≈ 8.93, 9.26 µm).
However, the major drawback into commercializing the technique is the fact that detectors at the
above mentioned ranges are expensive, and thus the need to perform up-conversion of the
signals into the visible range so as to render the currently available and cheap Si-based
detectors usable is a need of the hour. Ideas to use series second harmonic generators (SHG)
on the signals are not so feasible owing to the expensive crystals for the working range of
interest and the loss of the efficiency in each steps involved, whereas the use of single-crystal
Er2O3-on-Si (EOS) based detectors or application of nonlinear crystals for achieving the up-
conversion can be a possibility and open for collaborative ideas.
Figure 1: Schematic showing the experimental setup for detection of the various possible gas vapors around 6-10 µm
absorption edges.