FocusMonitor FM+

The PRIMES FocusMonitor FM+ analyzes and measures laser beam sources in material processing. FM+ determines the beam properties of focused laser beams, in addition to their geometric dimensions, focal position, the beam parameter product and the beam quality factor. The integrated z-axis allows for automatic measuring of entire caustics up to four Rayleigh lengths – facilitating measuring compliance with quality standards.

An update to the original FocusMonitor, the FM+ features new electronics designed to meet current and future requirements for signal processing and a new motherboard with a 16-bit A/D converter. An Ethernet interface allows for fast and secure data exchange with computers or system controllers. The new mechanical design also accommodates upside down installation without additional components.



The FM+ is an opto-mechanically scanning measuring system that scans the laser beam with a special measuring tip. The unit is equipped with a small hole (typically with a diameter of approximately 20 µm) that lets through a small section of the laser beam. Two reflecting mirrors guide this portion of the laser light to a detector selected and configured depending on the laser power and wavelength. This makes it possible to measure the different laser beam sources and systems solely by selecting the optimal measuring tip and corresponding detector. The high orbital velocity of the rotating measuring tip facilitates analysis of high power densities.

A very high signal-to-noise ratio is achieved thanks to the dynamics of the analog-digital converter used. Very low intensities are shown with equal precision next to the high peak intensities. That is one of the requirements for automatically measuring caustics in the area near the focal point over at least four Rayleigh lengths in accordance with ISO 11146.


The primary beam parameters are:

  • Focal dimensions
  • Position of the focal point in space
  • Power density distribution
  • Symmetry of the power density distribution
  • Diffraction index M2 or k
  • Beam parameter product



With the new LaserDiagnosticsSoftware (LDS), the FocusMonitor FM+ offers considerably more functionality. In addition to the faster Ethernet connection, the LDS enables the fully-, semi-automatic or manual measurement of the beam distribution as well as the determination of the beam position and the beam dimensions. Measurements with a higher resolution and freely selectable ROI (region of interest) can be recorded. Furthermore, the FM+ has a higher dynamic range, which makes it possible to determine beam radii even at a poorer S/N ratio. Further parameters like beam waist diameter, divergence angle, Rayleigh length and beam quality M² are examples of properties, which will be calculated by the LDS based on the measuring results from the FM+.

The number of measurement planes is freely selectable, typically between 11 and 21 planes. Complete measurement data sets and computation results can be stored and, if necessary, loaded for further measurements with specified basic data sets as a reference. Alternatively to the new LDS, the FM+ runs in combination with the previous version LDS 2.9. Both versions are compatible with Windows 7® or higher operating systems.



Measuring Tips and Detectors
For accurate operation, the FM+ needs to be equipped with a suitable measuring tip/detector combination. The replacement of both the detector and the measuring tip can be done in a few minutes. Adapted measuring tips and detectors for various divergences as well as wavelengths of different beam sources are available. The detectors are equipped with an EEPROM, enabling communication with the LDS. The resolution of the detector and the size of the measuring window can be adjusted within the software.

For the wavelength of CO2 lasers (λ = 10.6 μm), mainly pyroelectric detectors, such as the DFCM+, together with CO2 high power measuring tips have to be used. For the analysis of solid-state lasers in the range between 400 and 1100 nm, the detector DFY-PS+ with a high dynamic range and an automatic signal adjustment is employed. The DFIG-PS+ detector is available for wavelengths between λ = 1 – 2.1 μm. These detectors are generally combined with a NIR high div measuring tip. There are additional measuring tips for diode laser radiations, which are often highly divergent. In addition, specially adapted detectors, e.g. with an optimum signal-to-noise ratio or measuring tips with increased or reduced sensitivities can be provided.

As hardly any beam power is absorbed during beam diagnosis, the FM+ is ideally implemented in combination with a power meter such as the PRIMES PowerMonitor. Thereby, the power can be monitored simultaneously to the caustic measurement and all radiation is safely absorbed.