Focus Measurement

A scanning diagnostics system for the analysis of continuous wave laser beams

The FocusMonitor (FM+) is a scanning diagnostics system for the analysis of laser beam sources for laser material processing in laser beam welding, cutting as well as surface processing and others. 

FocursMonitor, FM+

The FocusMonitor measures the beam properties of focused laser beams. In addition to the geometric dimensions of the focused laser beam, the focus position in space, the beam parameter product as well as the beam quality factor M² are determined. The integrated z-axis enables the automatic measurement of complete caustics over up to four Rayleigh lengths.

The successful FocusMonitor has evolved into the FM+, providing new electronic features to meet the current and future demands of signal processing. A key part is a new main board with a 16 bit AD converter. The FM+ is operated with the new version of the PRIMES LaserDiagnosticsSoftware and is equipped with an Ethernet interface for fast and secure data exchange with computers or system controls. The FM+ can be mounted overhead without the need for additional hardware.

The Principle   

The FM+ is an opto-mechanically scanning diagnostics system. The laser beam is scanned using a specialized measuring tip. A small pin hole (typical diameter: 20 μm) in the measuring tip samples a small part of the laser beam. The sampled part of the laser beam is guided onto a detector element, which is chosen according to the power and wavelength of the laser radiation.

Hence, different laser beam sources and –systems can be measured at their maximum power simply by choosing the optimum measuring tip and detector. The high speed of the rotating measuring tip enables the analysis of high-power densities. Due to the high dynamic range of the employed analog digital converter, a very good signal-to-noise (S/N) ratio is achieved. High peak intensities as well as very low intensities are displayed precisely. This is one of the prerequisites for an automatic measurement of beam caustics in the focus range over at least four Rayleigh lengths according to ISO 11146. 

FocusMonitor FM+ HPD (High Power Densities)

The latest innovation in the FocusMonitor FM+ family. Through continuous development and the special design of the new measuring principle FS³ (Fused Silica Sensor System), it is now possible to measure and evaluate laser beams with very high-power densities of up to 50MW/cm2. Beam diameters of 100μm – 1200μm can be evaluated. The revolutionary design and the new functionality of the FocusMonitor FM+ HPD are available for beam sources in the wavelength range of 1.0 – 1.1μm.

With the FocusMonitor FM+ HPD, we present a milestone in the caustic analysis of laser beams in previously difficult to evaluate power ranges, which find use in cutting applications, for example.

 

Subject to change without notice.

Modular Focus Analyzing System for micro manufacturing

The MicroSpotMonitor-Compact (MSM-C) extents the product family of camera-based focus analysis systems. It is a modular, configurable measuring system, optimized for the limited space available in micro production plants.

Application

Due to the variety of measuring optics,  additional beam path components and deflection units (optional), the construction of the MSM-C can be changed. It ranges from a minimal installation height  of 70 mm to a storage space of 250 x 250 mm with a central beam incidence.

Technical description

The camera housing includes electronics, attenuation and power absorbers and has dimensions of about 230 x 120 x 60 mm (L x W x H). 

The MSM-C is water-cooled and can be operated with laser powers of up to 1 kW (multi-mode) or 100 W (single-mode). 

As an alternative, an air-cooled version can be operated  up to 50 W.

Technical data

Power range 10 mW to 1kW
Laser Power up to 1 kW (multi-mode)

up to 100 W (single-mode)
Wavelength

340-360 nm (up to 10 W)


515-545 nm (up to 50 W)

1030-1090 nm

(1000 W multi-mode - 100 W single-mode
Repetition frequency in Videomode from 1 s
Beam dimensions 10 µm up to ca. 1 mm (according to measuring optics)
Beam position Accuracy: 5 % of beam diameter (lateral)

Technical Data camera module: 

  • Available measuring optics:

 

3.3-times (NA=0,1 - 1 kW)@ 1064 nm
5-times (NA=0,2 - 500 W)@1064 nm
10-times (NA=0,2 - 200 W)@1064 nm

  • Field objective for reduction of magnification (x 0.3)
  • Camera dimensions: L x W x H = 230 mm x 120 mm x 60 mm
  • Triggered mode of single pulse up to typ. 10 kHz
  • Pulse lengths from approx. 80 fs to an continuous operation can be measured
  • Optional: beam path components and deflection units for an optimal installation in the plant.

Options for the absorption of the beam power and the power measurement: 

  • water-cooled absorber
  • air-cooled absorber up to 50 W
  • cooling unit with air-water-heat exchanger up to 200 W

Measuring position and dimension of the focus

The MicroSpotMonitor is the favorite tool to investigate, qualify or simply to check (for quality control reasons) very small laser beams for instance used in laser micro machining.

Application

The MicroSpotMonitor measures the power density distribution automatically at different z-positions of the beam within a few minutes.

The following results are obtained:

  • Power density distribution at the measurement planes
  • The dimensions of the laser focus: diameter, divergence, rayleigh length
  • The focus position in space
  • Beam propagation ratio M²

The measurements are based on ISO 11145/11146

Technical description

The Laser Beam is scanned with a rotation pinhole (about 20 µm in diameter). This pinhole is used to couple out a small part of radiation in the focus region. With two mirrors the signal target is directed to the detector. Then the electrical signals are digitized with work pieces power densities of several MW/cm². The divergence of the radiation in most cases is low. This leads to f- numbers (ratio of focal length of the optics to diameter of the unfocussed beam) of normally b12 bit resolution and transferred to a computer. The positions of the scanning traces (x) are movable in y- and z- direction. So it is possible to measure a complete beam caustic within some minutes.

In the standard configuration the FocusMonitor is designed to measure IR- lasers (CO2 or Nd:YAG- laser) with a output power of several hundret watts up to many kW. These lasers reach in standard applications like cutting or welding of typical metallic igger than 4.The central unit of the FocusMonitor is the scanning mechanic with the control of the three axis of motion.

With different detectors and special measuring tips it is easy to expand the field of applications of the FocusMonitor. So it is possible to detect also highly divergent beam as generated by high power diode lasers. Also beams with more than 10 kW CO2- laser radiation can be analyzed. But even higher laser sources with a power of only a few watt can be measured.

Due to the high speed of the measuring tip (up to 10- 40 m/s) no material ablation takes place on the surface. In addition the measuring tip is made of material which is corrosion and temperature resistant.

The dynamic of the used 12 bit analog to digital converter ensure a high signal to noise ratio. This is - beside other features - the basis for an automatic caustic measurement accroding to the ISO 11146 standard. The request of the ISO is to measure within the direction of beam propagation four times the Rayleigh length minimum. Within the measuring range the power density varies a factor of four and the signal to noise ratio should not be higher than 100:1.

The relative spatial resolution of the FocusMonitor can be adjusted between 32x32 up to 256x256 pixel in the scanning array. So it is possible to detect even small disturbances in the power density. With the standard settings of 64x64 pixel measurements with high speed and sufficient accurracy can be realized.

Technical data


Beam diameter 10 µm up to 2 mm
Spectral region 248 nm up to 1100 nm
Max. average power 200 W (from ca. 1 mW)
Max. energy density Damage threshold of the measuring optics up to  3 J/cm² at 10ns pulse length
Max. power density 10 GW/cm² im cw-Betrieb
Dimensions (H x L x W) 
(plus connectors)
202 mm x 219 mm (+30 mm to measuring position) x 429 mm


Control and presentation

The measurement of the focus is done using a diffraction limited optics projecting the image of the power density distribution onto a CCD-sensor. The magnification of the various objectives is 1:1 to 1:30. This enables the user to measure even highest power densities.

Between objective and detector, a sophisti-cated attenuation system is integrated.

The CCD-sensor itself has a dynamic of about 55 dB at a fixed integration time.

With the additional control of integration  time (12 µs to 200 ms) the dynamic range can be expanded to about 80 dB. This leads to a range of more than 130 dB. 
In every case, the dynamic is sufficient for a caustic measurement, which requires  a range of more than 4 Rayleigh lengths, according to ISO 11146. With the integrated z-axis the MicroSpotMonitor can run such measure-ments within around a minute.


Automated Beam Control in Production with High Brightness Multikilowatt NIR-lasers

The HighPower-MSM-I is designed to work in rough industrial environment: automated beam monitoring in continious working manufacturing facilities.

Application

Beam power, focus position laterally and in depth, focus geometry in form of diameter, divergence and Rayleigh length, beam parameter product and M² as well as further derived parameters can be monitored. The measured values are compared to preset limit- and critical values. Hence, an alarm is generated.
Fully automated measuring programs are running using the communication between system control and laser source. The measuring results are given back to the system control with a corresponding evaluation. All measuring results and status parameter of the measuring decive can be saved with a special timestamp.

Besides an automated beam parameter measurement within a production environment, the device is also suitable for the qualification and verification of beam parameter of beam sources, laser machines and processes in development, production, maintenance and service.

 

Technical description

The device is provided with a comprehensive internal  sensoric for self controlling  and for identification of internal malfunction sources. Additionally, a further port for a secondary light conducting cable enables an automatic testing of all measuring functions and the status of the internal optics. A power measurement test can be done due to a  corresponding internal heat source.

Technical data

 Beam power  500 W bto 10 kW
 Demand interval power  10 sec, (thermal time 90 sec)
 Beam dimensions  15 µm to approx. 3 mm (depending on measuring optics)
 Focus position  3 per cent focus diameter (lateral)
   75 µm + 5 % Rayleigh length
 Divergence  50 mrad to 400 mrad (round angle)
 Rayleigh length  30 µm to 30 mm
 Time resolution beam measurement  from 2 sec (depending on device settings)
 Astigmatism  to 30 mm
 Tilt angle  0,1 ° to 10 °



  • Beam aperture with refence geometry  (incl. mechanical shutter)
  • Fiber aperture (Fiber plug D, different fiber plug-ins on demand)
  • 3 support surfaces for horizontal and vertical beam entrance
  • 32 digital I/O-ports for communication  of device and laser
  • Dust proof housing
  • Gas shielding of beam entrance
  • 4 internal protective glasses at the exchange-plate
  • Function control  (elektronics, temperature, water, compressed air)
  • Self-test function for power, internal protectice glasses and beam
  • Dimensions: L x W x H = 750 x 400 x 550 mm
  • Weight: approx. 150 kg