Beam combiner and monochromatic beat detector

  • Flexible beat detection units
  • Designed for use with DFC and DL pro
  • Stable and compact

TOPTICA's beat detection consists of two flexible modules: DFC BC and DFC MD. Separating beam combination and beat detection into two units allows for placing them at different locations. The DFC BC and DFC MD units are specifically designed for a combination of the DFC with TOPTICA's DL pro tunable diode laser series, but can also be used with other cw lasers.


The DFC BC (beam combiner) spatially overlaps the DFC output with a cw laser. The relative intensities between both beams can be adjusted internally. If a fixed splitting ratio is acceptable the DFC BC can be replaced by an all-fiber combiner. The unit can also be used individually as an ultra-stable combiner and fiber coupler for any pair of laser beams.


Fiber beam combiner for DFC and cw-laser, 980 nm, 1030 nm, 1300 nm, 1550 nm.


The DFC MD (monochromatic detector) detects a beat-note between the DFC and a cw laser with the highest possible signal to noise ratio. Using a grating-based adjustable filter with a bandwidth of 10 GHz and a tuning range of several 10 nm, it filters a narrow spectral component of the combined cw laser and DFC. The unit also includes a low-noise photodetector and amplifier to detect the RF beat-note signal. It enables three different operation modes:

  • Measurement of the beat frequency using the beat monitoring unit of the DFC CORE module
  • Active locking of  the cw laser to the DFC (requires additional locking electronics for the cw laser)
  • Locking of the DFC to the cw laser (requires DFC CORE+ version)

The photodetector can be detached from the DFC MD unit to convert it into a monochromator serving as narrow band frequency filter. The output of the monochromator can be fiber-coupled or attached with slits of different sizes defining the filtering bandwidth.

  • Beam combiner and monochromatic beat detector