FBH developed fiber coupled pump modules for chirped pulse amplification thin disk lasers
940 nm QCW Pump Modules for 6 kW out of Fiber
Fig. 1: Beam propagation simulation of 28-level laser stacks coupled into a 1.9 mm fiber
Fig. 2: Chip design (stretched vertical axis)
Fig. 3: Sandwich-like chip mounting
Fig. 4: Completed QCW pump module with P/I-characteristic
In a joint project with the Max-Born-Institute the FBH developed fiber coupled pump modules for high repetition rate chirped pulse amplification thin disk lasers of the Joule class. The Yb:YAG system works at up to 200 Hz repetition rate and emits ps pulses.
The diode laser pump modules are designed to emit 6 kW, 1 ms pulses with 200 Hz repetition rate from a 1.9 mm fiber. Therefore, two laser diode stacks whose beam parameter product is fitted to the fiber input are geometrically coupled by a stack of reflecting prisms (Fig. 1). Each stack delivers > 3 kW optical output power and consists of 28 levels which are operated at 110 W.
The chips have a lateral aperture of 1.2 mm which is fitted to the fiber input. The cavity length is 6 mm. Some special measures ensure the pulse operation with high excitation levels (Fig. 2). These include stripes of shallow implantation, deep implantation and grooves beside the cavity and an extreme, double-asymmetrical super-large optical cavity.
Measured data of the mounted chips:
- COD level 250 W,
- conversion efficiency 60% (@110 W),
- vertical far field angle 43° (95%),
- lateral far field angle 12.5° (95%, 110 W).
The newly developed type of mounting is shown in Fig. 3. In order to achieve an efficient passive cooling two measures have been taken. Firstly, two expansion-matched CuW blocks are soldered to the chip. Secondly, the dissipated heat flows to both sides from the chip to two DCB water coolers which are soldered to the left and right sides of the CuW blocks (red arrows). Two Al2O3 spacer plates beside the chip protect it from outer pressure. All solder joins within the robust CuW/chip/CuW sandwich are made of AuSn.
Stacking the sandwiches, mounting the DCB-coolers and fabricating the body of the complete pump module is carried out by the C2GO inprocess solutions GmbH. The module with the laser cable (fiber) and the output power/current characteristics are shown in Fig. 4. It demonstrates the simple and robust design specialized for QCW pump modules, which is putted to the test right now.
Publications:
- R. Platz, B. Eppich, P. Crump, W. Pittroff, S. Knigge, A. Maaßdorf, G. Erbert "940nm Broad Area Diode Lasers Optimized for High Pulse-Power Fiber Coupled Applications" IEEE Photonics Technol. Lett., vol. 26, no. 6, pp. 625-628 (2014).
- W. Pittroff, B. Eppich, G. Erbert, R. Platz, D. Tyralla, G. Tränkle, "Simple design for fiber coupled 9xx nm kW-QCW pump module with high duty cycle based on customized chips and lateral heat removal” Contribution to SPIE Photonics West 2014, Paper8965-40
Contact:
Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH)
Gustav-Kirchhoff-Straße 4, 12489 Berlin
Tel.: +49(0)30 6392-2626/-2600
Fax: +49(0)30 6392-2602
Email: fbh(at)fbh-berlin.de