Many laser applications require not only knowledge and control of the intensity distribution of a beam, but also of its propagation characteristics which is mainly determined by the wavefront. Real-time wavefront monitoring is e.g. essential for optimizing the beam focus by precision adjustment of all optical beam line elements. Wavefront sensors based on the Hartmann or Hartmann-Shack principle provide simultaneous recording of beam profiles and wavefronts, allowing, in case of coherent radiation, also numerical propagation of the beam.
The basic principle dates back to 1900 and is based on splitting-up the incident beam into a large number of single beamlets, either via a pinhole array (Hartmann) or a microlens array (Hartmann-Shack). Each of these beamlets generates a spot on the camera detector, whose centroid relative to a reference position defines the local propagation direction. The phase distribution (wavefront) is then reconstructed by integration over the propagation directions. A real time Zernike analysis of the wavefront allows precise evaluation of beam aberrations (e.g. sperical aberration, astigmatism, coma), either of intrinsic nature or caused by external optics. In addition, by integration over all spot intensities the beam profile is determined.
For coherent light sources all relevant beam parameters, such as beam diameter, divergence and M2, are computed from wavefront and beam profile in real-time, i.e. within a single measurement. This is particularly important in case of pulsed or fluctuating laser sources. In addition, Fresnel-Kirchhoff integration accomplishes prediction of intensity profiles at any position along the beam axis. This holds especially for the beam profile around the beam waist, where measurements are often extremely difficult due to the high intensity. This way, beam focusing can be optimized.
Since many years, ProOpto offers camera-based Hartmann-Shack sensors for comprehensive characterization of laser beams in cooperation with Laser-Laboratorium Göttingen. Depending on angular / spatial resolution an wavelength, a large number of microlens arrays (focal length, lens diameter) as well as cameras can be adapted for customized wavefront metrology.
All cameras can be easily connected to PC or notebook via USB or GigE interface (Plug&Play).