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concept setup
First setup with four laser bars

Rectified Polarisation Coupling for Diode Laser Bars

Modern material processing with lasers has increased demands in terms of power and power density which cannot be obtained directly with diode lasers.

To improve the power density of diode laser bars a multi-step polarization coupling was developed. The beam quality of the combined beam then possesses the beam quality of the single bar while the output power is scaled up considerably.

For that a multitude of laser bars are inserted into individual resonators which share the last section in front of the outcoupling mirror. Through a clever choice of spectral filters all lasers run on individual but intertwined spectral combs of longitudinal laser modes. The reuslt is an increase in power by a factor of roughly 1.8 per coupling stage.

Powers in excess of 500W have be shown and future developments promise values well above 1kW.

coupling scheme
Multiple lasers are polarization coupled. By means of a dispersive crystal polarization can be rectified again.

Principle of Coupling

An array of laser resonators is built so that they share the outcoupling mirror. One or more Lyot-filters separate different frequency components into the different channels which are each driven by a separate gain element.

From this arrangement of filters every diode laser can only oscillate on the wavelength that it is assigned to by the filter.

simulated spectra
Finite element simulations of spectra and angular distribution in two spatial and one temporal dimension.

Spectral Simulations

In close cooperation with Weierstrass-Institut for Applied Analysis and Stochastics (WIAS) in Berlin the corresponding resonators have been simulated.

By means of finite elements in two spatial and one temporal dimension the spectral behaviour and the angular distributions of the radiation could be determined. It can be seen that the individual lasers oscillate on intertwined spectra.

Due to the finite angular acceptance of the filters and other optical disturbances a certain amount of cross talk between the channels is unavoidable.

experimental spectra
Experimentally determined spectra of four intertwined laser bars

Experimental Spectra

Coupling four high-power diode-laser bars in a two-stage process delivers the expected intertwined spectra with very good spectral separation.

In the future it should therefore be possible to again almost double the output power of this once again polarized light by using a second such setup.

demonstrator with 500W output power
Demonstrator setup comprising four laser bars which can produce over 500W of output power

Demonstrator

A platform for four high-power diode-laser bars was developed together with monocrom.

With this demonstrator it was possible to generate a single coupled beam in excess of  500W optical power and a beam parameter product of  BPP<30mm mrad.

Further Information

  • Project partners:
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  • Specifications: 500W, BPP < 30, λ=976nm
  • Publication: JOSA-B Vol.36, No.7 (2019) C. Brée, V. Raab, J. Montiel-Ponsoda, G. Garre-Werner, K. Staliunas, U. Bandelow, M. Radziunas;
  • "Beam-combining scheme of high-power broad-area semiconductor lasers with Lyot-filtered reinjection: modeling, simulations, and experiments"
  • Project funding: 01QE1650B (HIP-laser)
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