Experimental techniques and instrumentation

Experimental techniques and instrumentation

The investigation of the detailed spatio-spectral properties of light sources requires the acquisition of complementary data with high resolution.

We have developed an instrument [1] capable of simultaneously acquiring intensity and spectral properties of a light beam with high spatial resolution both in the near and in the far field.

The instrument consists of a fiber which samples the optical field in a given plane (preferably in the near- or far-field, which can be obtained by relay optics) mechanically scanned in 2-D with a computer-controlled high-precision translation system. The sampled light is split into two channels, one measuring the intensity (with suitable detector) the other one going to an optical spectrum analyzer which provides the full optical spectrum (and its peak wavelength). The fiber can be properly oriented at the input to optimize incoupling and avoiding feedback into the source (very important for lasers!).

Its main characteristics are:

• • spatial resolution down to ~6 mm (single-mode fiber diameter)

  • high mechanical reproducibility (better than 1 mm)

  • configurable acquisition matrix (aspect ratio, sampling distance adjustable independently in the two directions, number of points)

  • simultaneous intensity-spectral information

  • 1-D or 2-D scans

  • competitive performance in intensity profile recostruction

  • high dynamic range

  • response linearity (no cross-talk between "pixels")

  • very high sensitivity

  • robustness

  • fiber incoupling tolerance

[1] T. Wang and G.L. Lippi, Synchronous characterization of semiconductor microcavity laser beam, Rev. Scie. Instr. 86, 063111 (2015). Preprint available on http://arxiv.org/abs/1506.01794

Intensity profile emitted by a 980 nm VCSEL (Ulm Photonics)