Yosuke Mizuyama

Despeckling fly’s eye homogenizer for single mode laser diodes

A novel flys eye homogenizer for single mode laser diodes is presented. This technology overcomes the speckle problem that has been unavoidable for flys eye homogenizers used with coherent light sources such as single mode laser diodes. Temporal and spatial coherence are reduced simultaneously by introducing short pulse driving of the injection current and a staircase element. Speckle has been dramatically reduced to 5% from 87% compared to a conventional system and a uniform laser line illumination was obtained by the proposed flys eye homogenizer with a single mode UV-blue laser diode for the first time. A new spatial coherence function was mathematically formulated to model the proposed system and was applied to a partially coherent intensity formula that was newly developed in this study from Wolfs theory to account for the results.

A new fly's eye homogenizer for single mode laser diodes

A novel flys eye homogenizer for single mode laser diodes is presented. Laser speckle has been removed and a uniform laser line illumination has been obtained for the first time with the proposed flys eye homogenizer incorporating a single mode laser diode by introducing a staircase element and short pulse switching of the injection current. The former degrades the spatial coherence of the adjacent beamlets emanating from the microlens arrays while the latter simultaneously shortens the temporal coherence time so that the necessary optical path lengths in the staircase element become realistic in size. An average speckle contrast of 5% was achieved with the new flys eye homogenizer whereas the standard flys eye homogenizer at a CW driving yielded a high contrast of 87%. The diffraction theory for partial coherent light based on Wolfs formulation was extended to a simplified model of the new flys eye homogenizer. The effect of the pulse width on the speckle contrast of the laser line illumination is experimentally shown and is discussed through a detailed analysis of the power spectrum and the fringe visibility, and a numerical study on the Dirichlet kernel based on the derived formulation for the intensity.