Centerpieces of life science applications – 1180-nm-DBR-tapered diode lasers with high spectral radiance

Laser sources emitting in the yellow spectral range are key components for many life science applications, such as medical applications and fluorescence spectroscopy. Since this spectral range is currently not directly accessible with laser diodes, nonlinear frequency doubling (SHG) can be used as a way out. Therefore, laser diodes are required that emit at 1180 nm and feature a high spectral radiance.

After extensive research, FBH has successfully developed advanced diode lasers that are based on epitaxial laser structures using InGaAs quantum wells (QW) on GaAs-substrates. To cope with the high pressure load in the QW, crystal growth was optimized [1]. DBR tapered diode lasers (DBR-TPL) were realized based on this optimized epitaxial structure. Initially, DBR-TPL with a total length of 4 mm enabled continuous-wave operation of more than 2,000 h at an optical power of more than 2 W [2], [3].

Meanwhile, we were able to triple the reliable emission of a DBR-TPL by using a larger component. The assembled 6 mm long lasers (TA-section length: 4 mm; RW-section length: 2 mm with a 1 mm integrated DBR-grating) yield an optical output power of more than 9 W at a TA-current of 15 A and an RW-current of 400 mA (Fig. 1). The spectral emission is longitudinal single-mode emission between mode hops.

These devices feature a narrow spectral width and an excellent beam quality with a power content of more than 75% in the central lobe at 8 W. A step-stress lifetime test resulted in a demonstrated operating lifetime of more than 3,000 hours at an optical power of 7 W without failure (Fig. 2).

Due to their compactness, these monolithic diode lasers are paving the way for high spectral radiance laser sources to be used in efficient single-pass SHG. Also, they will enable the miniaturization of existing laser systems for bio-analytics and fluorescence spectroscopy.

Publications

[1]    Bugge, F., Bege, R., Blume, G., Feise, D., Sumpf, B., Werner, N., Zeimer, U., Paschke, K., Weyers, M., 2018. Lifetime behavior of laser diodes with highly strained InGaAs QWs and emission wavelength between 1120 nm and 1180 nm. J. Cryst. Growth 491, 31–35. https://doi.org/10.1016/j.jcrysgro.2018.03.034

[2]    Paschke, K., Blume, G., Brox, O., Bugge, F., Fricke, J., Feise, D., Hofmann, J., Wenzel, H., Erbert, G., 2015. Watt-level continuous-wave diode lasers at 1180 nm with high spectral brightness, in: Proc. SPIE. pp. 93480X-93480X. https://doi.org/10.1117/12.2076340

[3]    Paschke, K., Blume, G., Ginolas, A., Feise, D., John, W., Werner, N., Bugge, F., Sumpf, B., 2018. Reliable 2 W DBR-Tapered Diode Lasers Lasing at 1180 nm Based on Highly Strained Quantum Wells, in: 2018 IEEE International Semiconductor Laser Conference (ISLC). Presented at the 2018 IEEE International Semiconductor Laser Conference (ISLC), pp. 1–2. https://doi.org/10.1109/ISLC.2018.8516251