Characterization of tapered diode laser bars for the use in high-power diode laser systems

Abstract

For further development in beam quality of high power diode laser systems a new type of diode laser bars has been realized recently. Compared to commercially available broad area diode laser bars the lateral design of tapered diode laser bars consists of a ridge waveguide and a tapered section, where the tapered structure determines high output power and the high brightness is provided by the ridge waveguide structure. Unfortunately the different lateral structure leads to astigmatism effects which are also thermally affected in continuous wave operation. Hence in terms of diode laser systems with essentially fast- and slow-axis collimation micro-optics the full characterization of tapered diode laser bars is necessary. Where the wavelengths and divergences of tapered diode bars are relatively easy to measure, the beam profile with its apparently inside the tapered structure located lateral source is not. With a telecentric optics the caustic of the individual emitters of the bars are detected by the use of a fiber sensor with a resolution of 10 μm in fast- and slow-axis direction. Subsequently with beam analysis software the astigmatism can be calculated. As a result of several measurements of tapered bars of different wavelengths we detected good homogeneity over the bar concerning the amount of astigmatism but a slight current dependency. So particularly with regard to beam shaping micro-optics the application to high power diode laser systems seems to be sophisticated so far.