Beam Profile Improvement of a High-Power Diode Laser Stack for Optoacoustic Applications Articles uri icon

publication date

  • April 2017

issue

  • 4

volume

  • 38

International Standard Serial Number (ISSN)

  • 0195-928X

Electronic International Standard Serial Number (EISSN)

  • 1572-9567

abstract

  • Recent advances in high-power diode lasers (HPDLs) technology allow their use as potential sources for optoacoustic (OA) applications, due to their high repetition rates (a few kHz), low costs and sizes. However, some OA applications require pulse energies in the order of mJ that cannot be provided by the only HPDLs (several mu J). The employment of diode laser bars (DLBs) and stacks (DLSs) significantly increases the energy per pulse up to several mJ, but they require more optical elements for collimation in fast and slow axes. In this work, we show an 808 nm DLS emitting optical nanosecond pulses with currents of similar to 200 A and supplied by a customized current driver. We only collimate the beam in the fast axis by disposing the core of 200 mu m optical fibers as collimating lenses along each bar of the stack, and we discuss the improvement of the beam profile. The results demonstrate that the beam profile is notably improved with the optical fiber lenses, and a 6.4 mm x 4.3 mm light spot is obtained by using a conventional focusing lens. Measurements report a total energy per pulse of 630 mu J in the spot, considering a pulse width of 850 ns and a repetition rate of 1 kHz. Finally, we focus the light spot into an absorbing inclusion (graphene oxide) hosted in a semi-transparent phantom to generate and detect high OA signals (similar to 355 mV(pp)). The results achieved demonstrate the capability of our DLS system to be applied in multispectral OA systems with final application in OA endoscopy and microscopy.

keywords

  • fast axis collimation; high-power diode laser stacks; optical fiber lenses; optoacoustics; photoacoustic microscopy; low-cost; tomography; system; collimation; excitation; fiber