The FocusMonitor is a device to measure the focused laser beam with high continuous output power. Quick and reliable radius, position and beam propagation ratio of the focused laser beam are determined even in an industrial environment.

Basics

The laser focus is the main control over the performance of laser material processing. It is the real tool in most applications of laser material processing. The following beam parameters and errors can be estimated by measuring the laser power density distribution in the focus region.

- focus radius
- position of the focus in space
- spatial power density distribution
- beam propagation ratio M2
- error in alignment of : laser resonators, telescopes,
- beam guiding systems and focusing optics

The focus analysis in an industrial environment has several goals :

- The beam geometry in the focus region should be
- measured and documented. Thus it is possible to detect
- even long term variations in the system, which results
- in changes of the focus quality.

Power range (depending on the measuring tip)

Power :

up to 15kW

maximum power density :

up to 30MW/cm2

Limiting factor is the energy on the measuring tip so only one of the two values can be run to the limit at the same time.

Function of the measuring system

2-dimensional scanning of the power density distribution of the laser beam in the xy-plane by fading-out a small part of the initial beam with a rotating pinhole. During measurement the beam is not absorbed within the device. For a safe operation it needs an external absorber.

Spatial measuring range

x-, y-direction :

0.25mm to 8mm with a factor of about 1,4 between the different windows

z-direction :

35mm or by option 120mm

Relative spatial resolution

in x-direction (number of pixels per trace) 32, 64, 128, 256
in y-direction (number of pixels per trace) 32, 64, 128, 256

Actuation of the system in x-axis

maintenance-free brushless DC-motor with crystal stabilized speed control

The rotational speed of the
measuring tip is adjustable :

1875rpm or 3750rpm - by option 7500rpm

Actuation of the system in y-axis

Motor with encoder and ball screw

Digitizing of the measured data

12 bit A/D-converter and prescaler

Measuring time

Standard setting with 64x64 pixels :

2.5s

Repetition rate of the measurement :

0.1Hz

Dimensions

dimensions (h x l x w) :

242mm x 135mm x 290mm (plus connectors)

weight :

6kg

Software

measuring results :

beam radius (86% and 2. moment),
beam position, power density distribution,
beam propagation ratio M2

measuring modes :

single measurement, automatic caustic
measurement, mean value, monitoring,
adjustment mode

presentation :

Isometry, False color, contour lines;
caustic, numerical review, symmetry check

data format :

PRIMES-format(binary) or MDF-format (ASCII)

Options-FocusMonitor

- measuring tips with a higher standing or with changed sensitivity
- rotational speed up to 7500rpm
- increase z-axis
- integrated shielding gas flushing
- detectors and measuring tips for different wavelengths and beam divergence.