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Scaling the Output Power of Laser Systems

The output power of a laser beam is increased without decreasing the beam quality, whilst still maintaining polarization.

For this several single lasers, mostly laser diodes, are arranged in external laser resonators which share the final section in front of the outcoupling mirror. By wisely choosing spectral filtering elements, all lasers oscillate on interlaced spectral combs of longitudinal laser modes. The result is an increase in output power by a factor of about 1.8 per coupling stage.

The initial beam has basically unchanged beam parameters (diameter, divergence, beam quality, beam propagation factor M²). Despite internal polarization coupling, the resulting beam is polarized at the exit mirror.

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.

spectral combs
Lasers emit intertwined spectral combs.

Spectra

The coupling happens through an intertwining of several comb-like spectra. A unique comb is assigned to each laser. If the gain-curve changes, for example because a higher voltage flows, new spectral lines can follow this alteration .

power scaling

Power scaling behaviour

Those lasers are mostly independent because each one has it's own resonator; this is why the powers add up. A certain crosstalk is inevitable due to residual divergence and spectral tails.

operating demonstrator

Demonstrator

With a demonstrator and by coupling four laser diodes it is possible to produce a polarized beam with about 500mW power and near diffraction limited beam quality.

Further Information