High-Power Diode Lasers Optimized for Low-Loss Smile-Insensitive External Spectral Stabilization

Low-loss smile-insensitive external frequency-stabilization of high power diode lasers enabled by vertical designs with extremely low divergence angle and high efficiency

“…Large vertical near fields have a further advantage: when laser bars are soldered onto a heat-sink, some mechanical deformation is always induced, leading to small differences between emitters within the bar in vertical position and pointing angle, collectively termed bar smile. When the vertical near field is significantly larger than the bar smile, losses will be minimized [21]. Finally, designs with narrow vertical far fields can enable high performance in novel wavelength stabilization configurations.…”

“…Finally, designs with narrow vertical far fields can enable high performance in novel wavelength stabilization configurations. For example, VHGs can be located in the un-collimated beam, simplifying the optical design (in this case, narrow far fields have been demonstrated to substantially improve both optical loss and locking range [21].) We illustrate here the expected benefit of narrow vertical far fields on fiber coupling efficiency for a diode laser module based on single emitters with a stripe width, W = 90 µm.…”

“…In previous work, just such a detailed comparison was presented, for ELOD1 devices as described in Ref. [21]. The reference material was also fabricated at the FBH, and is described in [13].…”

“…BA lasers stabilized using internal distributed Bragg gratings have recently demonstrated reliable powers and efficiencies (η E = 58% at P out = 10 W [13,14]) close to that of un-stabilized devices, and reduce the channel spacing to < 2 nm, due to their narrow spectrum and reduced temperature sensitivity (Δλ 95% < 1 nm and δλ/δT ~ 0.08 nm/K [13,14]). Wavelength stabilization of BA lasers using external gratings is also in wide use [7][8][9][10][11][15][16][17][18][19][20][21], and extremely narrow, highly temperature stable spectra are possible, even in high power systems (a linewidth of < 100 GHz and δλ/δT < 0.01 nm/K have been demonstrated). Such narrow, stable spectra are needed (for example) for pumping narrow lines in Alkali-laser systems (see [16,19] and references within).…”

“…We present here a summary of recent studies performed at the Ferdinand-Braun-Institut on BA lasers that have been specifically optimized for wavelength stabilization with external VHGs. These devices are termed throughout ELOD lasers, as they operate with extremely low vertical divergence, whilst sustaining high efficiency and high reliable powers [12,[21][22][23]. These ELOD designs were developed within the project SpektraLas, a part of the German national development program "INLAS", and their assessment for use in spectral beam combining systems is planned as part of the recently started EU program BRIDLE 1 .…”