Spectral beam combining of quantum cascade lasers in an external cavity

Abstract

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 [1], is also applicable to mid-infrared QC lasers. Within this concept, the output of multiple emitters from a 4.6 ?m 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

Infrared semiconductor laser modules for DIRCM applications

“…To overcome this limitation, the concept of spectral beam combining using an external cavity configuration has been applied to QC lasers, demonstrating the coupling of the output beams of up to 8 individual QC laser ridges, located sideby-side on a single semiconductor chip [10]. Fig.…”

“…Fig. 9 shows a schematic of the EC-QC laser configuration employed here for spectral beam combining of 4.5-5 µm emitting QC lasers [10]. The parallel output beams emitted by the individual QC lasers are collimated by a single custom made aspheric lens (transforming lens) and then directed onto a ruled grating with a blaze angle matched to the operating wavelength of the QC lasers.…”

“…Current record value for 4.6 µm emitting QC lasers is a maximum roomtemperature cw output power of 3.4 W in a laboratory setup [8]. Attempts to further increase the output power have been made (a) by increasing the emitting aperture width of a single emitter from typically ~10 µm to 100 µm, while employing a photonic crystal distributed feedback structure for maintaining a high beam quality, [9] and (b) by combining the output power of several narrow emitters located side-by-side on a single semiconductor chip in an external cavity (EC) setup (spectral beam combining) [10].…”

Spectral beam combining of discrete quantum cascade lasers

“…The phase mismatch and power modulation between the beams also makes the beam alignment rather difficult. Incoherent beam combining of lasers, on the other hand, has been widely investigated, such as wavelength beam combining of DFB array with a grating 8 , hollow waveguide beam combining 9 , spatial beam combining 10 , and spectral beam combining (SBC) [11][12][13] . Among them, SBC is an effective technique to achieve high output power with good beam propagation characteristics close to that of a single emitter.…”

Mid-IR semiconductor lasers for power projection and sensing

“…For both fast and slow axes, M 2 < 2 has been achieved. 7 A prominent application of OPSDL/QC-laser modules is directed IR countermeasures (DIRCM). Such systems protect aircraft against IR-guided missiles launched, for example, by man-portable air-defense systems (known as MANPADS).…”