Different approaches to power scaling of 4.5- to 5-µm emitting quantum cascade (QC) lasers by multiemitter beam combining are investigated. Spectral beam combining of linear arrays of QC lasers consisting of several individual emitters located side by side is demonstrated as a first variant, using an external cavity equipped with a diffraction grating and a partially transmitting output mirror providing wavelength-selective feedback to each emitter. In this way, spectral beam combining of up to eight individual QC lasers is achieved with an optical coupling efficiency of 60% for an array of six emitters. The resulting beam quality (M2 < 2 for both fast and slow axes) is close to that observed for single emitters. As a second approach, a linear array of QC lasers is coupled to a custom-made array of silicon microlenses positioned in front of the output facets of the QC lasers. This technique produces a set of closely spaced parallel output beams, strongly overlapping in the far field, without introducing any coupling losses. The resulting beam divergence is given by the aperture size of the microlenses, which is limited by the center-to-center spacing of the QC lasers (500 µm in our case).
In recent times the importance of Ladar systems for military applications increases rapidly. Prevalent application in this
area is 3D imaging. Conventional 3D scanning systems usually employ mirror-based mechanisms. Often these suffer
from bulky architecture and a fixed scanning pattern.
In this paper we describe an experimental monostatic Ladar setup with micro-optical bidirectional beam control. This
system offers certain advantages like random beam pointing and a compact design due to transmissive optical elements
with combined emitter and receiver channel.
Our publication depicts the setup of a Ladar demonstrator with micro-optical beam steering at lab-level. The range
finding system is based on time-of-flight principle at near infrared wavelength. Due to monostatic configuration a single
detector is used for start and stop pulse generation. The beam steering is accomplished with decentred micro-lens arrays,
which are driven by a precision alignment system. The micro-optical elements act as entrance and exit aperture
simultaneously. The results of laboratory characterization measurements and data evaluations complete our overview of the
We report on the concept, realization and performance data of infrared semiconductor laser modules serving as compact
and robust laser sources for a Directed Infrared Countermeasures (DIRCM) system. While the 2-2.5 μm atmospheric
transmission window is covered by a GaSb-based optically pumped semiconductor disk laser (OPSDL), delivering a
continuous-wave (cw) or temporally modulated output of ≥ 1 W with a high beam quality (M2 < 3), an external cavity
(EC) quantum cascade (QC) laser module is used to cover the 4.5-5 μm spectral range. The EC-QC laser concept allows
efficient spectral beam combining of the output of several QC laser located side-by-side on the same semiconductor chip,
while preserving the high-quality output beam of a single emitter. Both the OPSDL and the EC-QC laser have been integrated
into rugged laser modules, comprising also all necessary power supply and control electronics, ready for use in
In this contribution, we demonstrate that spectral beam combining in an external cavity (EC), a technique which has been
applied previously to shorter wavelength diode laser bars , is also applicable to mid-infrared QC lasers. Within this
concept, the output of multiple emitters from a 4.6 μm emitting QC laser chip is combined in a single, collinear beam.
The average power of an EC-QC laser module realized that way surpasses the output of a corresponding single emitter
by more than a factor of 4. Furthermore, the EC-concept allows a certain degree of wavelength tuning during operation.
The EC, consisting of a collimating lens, a grating and a partially reflecting outcoupling mirror, forces each laser to emit
at a unique wavelength defined by its offset relative to the main optical axis. The EC approach further ensures the
collinear directional and spatial overlap of the individual QC laser output beams forming a single combined output beam.
We report on the development and characteristics of infrared semiconductor lasers as compact and robust light sources
for Directed Infrared Countermeasures (DIRCM). The short-wavelength side of the 2-5 μm wavelength band of interest
can be covered by GaSb-based optically pumped semiconductor disk lasers (OPSDLs), delivering a continuous-wave
(cw) or temporally modulated multiple-Watt output with a high beam quality (M2<3). For the 3.7-5 μm wavelength
range InP-based quantum cascade (QC) lasers are the best suited semiconductor laser source, delivering several hundreds
of mW of average output power in a nearly diffraction limited output beam (M2<2). Further up-scaling of the output
power can be achieved for OPSDLs by intra-cavity coupling of several semiconductor chips as gain elements in a
multiple-disk cavity arrangement. For a 2.3 µm emitting dual-disk OPSDL, a doubling of the maximum roomtemperature
output power compared to that of a comparable single-chip OPSDL has been demonstrated. For QC lasers
power scaling by beam-quality-preserving beam combining has been demonstrated via polarization coupling of the
output beams of two individual QC lasers, yielding a coupling efficiency of 82%.
This paper at hand describes in details the work that has been carried out for fusing a commercial micro mirror sampling
element with TOF acquisition methods and known Hadamard multiplexing techniques for implementation of fast and
SNR optimized 3D image capture. The theoretical basics of TOF and Hadamard technique are presented and will be
complemented by theoretical explanation of utilizing them for 3D volumetric image generation. Finally measurement
results of scene image acquisition are going to be demonstrated and discussed as well as expanded by considerations
about possible applications in THz-imaging and the following research steps.