Improvement of spatial and temporal coherence of a broad area laser diode using an external-cavity design with double grating feedback

Abstract

Abstract:We demonstrate a novel technique for narrow bandwidth and highly improved lateral mode operation of a high-power broad area laser diode. The system uses simultaneous feedback from the first diffracted order and the zeroth reflected order of a diffraction grating. The two feedback paths lead to simultaneously improvement of the spectral and spatial properties of the laser diode. The laser system operates in the well-known asymmetric double-lobed far field pattern with the larger lobe being extracted as the output. The bandwidth of the output beam is measured to 0.07 nm, which corresponds to an improvement of a factor of 17 compared to the bandwidth of the freely running laser. The output from the system contains 54 % of the energy reaching the grating, or 75% of the power reflected into the zeroth order. The improvements in both the spatial and temporal coherence opens the possibility of using this laser system in applications such as frequency doubling and pumping of optical parametric oscillators.

Improvement of the beam quality of a broad-area diode laser using asymmetric feedback from an external cavity

“…However, these lasers suffer from uncontrolled emission of several lateral modes with a multi-lobed far field pattern (Samsøe et al 2004) because of their broad emitter width along the optical slow axis (Thestrup et al 2003). Several techniques, such as external cavities employing spatial filtering for mode selection (Wolff et al 2003), have been developed to improve the beam quality.…”

Spatial filtering in edge-emitting lasers by intracavity chirped photonic crystals

“…There are several demonstrated techniques to improve the beam quality in edge-emitting lasers, such as conventional spatial filtering using off-axis feedback [2], external cavity [3][4][5], tapered geometry [6], and evanescent spatial filtering [7]. High spatial quality single-mode beams can also be obtained by restricting the width of the active region of a ridge waveguide [8].…”

Coherent beam combining of high power broad-area laser diode array with near diffraction limited beam quality and high power conversion efficiency

“…Applying low anti-reflection (AR) coating to a BALD and employing external optical feedback to a BALD can limit the number of transverse modes. A variety of external feedback designs can limit the number of transverse modes of BALD and improve the beam quality [26][27][28][29][30][31][32][33][34][35][36][37][38]. The off-axis optical feedback was introduced to enhance one transverse mode and significantly increase beam quality of BALD [33,34,36,38].…”