Raw Beam Measurement

Measuring position and dimension of the focus

The LaserQualityMonitor (LQM) is a perfect measurement system for the charaterization and qualification of the beam propagation of lasers in the range of UV to NIR.

Furthermore, errors in the optical assembly of resonators and beam guiding systems are easily analyzed.

Typical areas of application are:

  • Laser development
  • Quality assurance in production of laser sources
  • Service and maintenance

Determine beam propagations, analyse faults

 
With the LaserQualityMonitor PRIMES offers an integrated solution for the quick and straightforward analysis of the beam properties of a beam source. The beam propagation of lasers from the UV to NIR range are characterised and certified with this measuring system. Furthermore, errors in the optical structure of resonators of beam imaging systems can easily be analysed.

This PRIMES innovation directly measures the power density distribution of a focal geometry that was created by integrated focusing optics. That makes this system unique in the market.

Advantage of this measurement method: Disturbances from diffraction structures, misalignment, asymmetries and other effects become directly visible in the measured power density distributions.


Compact, simple, individually expandable

 
The LQM characterises the parameters of a beam source automatically and quickly in conformity with ISO standard 11146. This is a compact and easy-to-align measuring system which is positioned directly in front of the laser to be measured and is aimed at the laser beam. The LQM essentially consists of a basic system in which all optical components and measurement functions are completely integrated. The base device can be supplemented by front-end modules with beam splitters, absorbers and alignment units and its power potential increased into the multi-kilowatt range. Fibre holders, collimators, neutral density glass filter inserts and additional measurement optics are available if needed. Furthermore, integrated measuring stations can be supplied as custom solutions.

 

Measurement methods – the principle

The characterisation of a collimated laser beam with Rayleigh lengths that are typically ten metres requires a significant measurement effort due to the very long measurement ranges of three to six Rayleigh lengths. This form of measurement is normally impossible for reasons of space. For this reason ISO 11146 recommends, in the alternative, the measurement of a caustic generated by focusing in order to determine the diffraction index M².

The LQM generates this device-internal caustic by focusing the irradiated collimated laser beam. The focussed beam is displayed enlarged on the CCD chip via several integrated attenuators and a lens. From the two-dimensional power density distribution measured in this way, the LaserDiagnoseSoftware determines the radius, position and orientation of the beam. Through the procedures of this measurement system, and repetition of the measurement at various positions in the device, all parameters necessary for the description of the artificial caustic are determined. The electronic exposure time control of the CCD chip expands the dynamic range of the system. This means that in general it is not necessary to alter the filters during a measurement.

Due to the laser beam being thus focused and characterised, the measurement can be shortened from several metres to a few millimetres. The M² value can be easily determined in this fashion, since it is ensured that the optics used for focusing do not generate imaging errors which influence the beam to be measured. The values of the beam parameters of the focused laser beam are calculated back to the values of the collimated beam in accordance with ISO 11146.

Measured beam parametersBeam waist diameter / beam dimensions

  • Waist position / focal position with reference to the beam entry into the LQM

  • Beam radius

  • Far field divergence

  • Rayleigh length

  • Divergence

  • Beam propagation factor k

  • Diffraction index M²


Measuring device for the characteristics of the unfocused laser beam

The CameraMonitor 10.6 is a camera-based measuring system analyzing IR laser radiation at 10,6 µm wavelength.

  • Determinatoin of beam width and beam position based on the measured power density distribution
  • Intuitive grahical user interface
  • High dynamic due to a 14 bit A/D
  • Quartz-stabilized motor drive of the rotational axis
  • Power range 100 W - 20 KW
  • power density range 100 W/cm2 - 10 kW/cm2 >20kW
  • Different apertures matched to the applications between 40 mm and 100 mm

Application

The laser beam is scanned with a rotating mirror So a small part of the beam is faded-out and directed to the detector.During the motion of the mirror the incoming signal is digitized and transmitted to acomputer. The position of the scanning track is changed by a linear motion in y- direction. The 12 bit A/D- converters and a resolution of 128x256 pixel enables an exact analysis of even small pertubations. operation laser-induced variations of the beam parameters cause a decrease of processing quality and velocity. The exact analysis of the true reason is ordinarily rather complicated, since other phenomena like variation of the focal position or the nozzle's adjustment have similar errors. At this point a detailed analysis of the'raw' laser beam between outcoupler and focussing optics is a reliable method to detect variations of the beam diameter, bad mode-structure or wrong beam position.

With the BeamMonitor from PRIMES the customer gains the opportunity of quick and reliable diagnostics of the beam parameters. The BeamMonitor is a device to determine the spatial power density distribution of high power CO2- und Nd:YAG - Lasers.

The beam diameter and position are calculated from these data.

Technical description

The laser beam is scanned with a rotating mirror So a small part of the beam is faded-out and directed to the detector. During the motion of the mirror the incoming signal is digitized and transmitted to acomputer. The position of the scanning track is changed by a linear motion in y- direction. The 14 bit A/D- converters and a resolution of 128x256 pixel enables an exact analysis of even small pertubations.The device is designed for operation in rough industrial environments.

Technical data

BeamMonitor 40 mm


Beam Data to be acquired

  • Maximum power density (cw): dependent on scanning mirror design up to 10 kW/cm2
  • Clear aperture: 40 mm
  • Maximum beam radius (86 % = 1/e2): approx. 12.5 mm

Measurement System

  • Function: Two - dimensional scanner to determine power density distribution of the laser beam in x- and y plane by scanning a partial beam due to a rotating mirror. The complete beam transversed the device and needs to be trapped during the measurement cycle.
  • Dimension of the scalable measurement window: Range from 3.3 x 3.4 to 40.0 x 40.0 mm with a scaling factor of approx. 1.4
  • Spatial resolution: towards x (# of measured dots per track) 32, 64, 128, 256; towards y (# of tracks per image) 32, 64, 128
  • Mirror driver for x - axis: maintanance - free brushless DC - driver with quartz - stabilized speed - control.
  • Mirror driver for y - axis: Driver with absolute encoder and ball screw spindle
  • Measurement data digitizing: 14 - bit AD - converter
  • Measurement cycle: Standard measurement window with resolution of 64 x 64 (4096 dots): 2.5 s ; repetition rate approx. 0.2 Hz

Power supply and communication bus

  • Electrical power supply: 24 V DC ± 5 %
  • Current consumption: max. 1.8 A; standby consumption 0.4 mA
  • Electrical connectors: 2 x PRIMES - RS485 - bus D - sub - min
  • Communication: The incoming RS 485 bus - signal will be converted for the serial PC COM port. The PRIMES software with graphical - user - interface operates under Windows operating systems, like WIN 95/98, NT, WIN 2000, XP

Mechanical Dimensions

  • Dimensions (LxWxH): 243 mm x 146 mm x 76 mm ( plus connector)
  • Weight: 2,6 kg

Software

  • measuring results: beam radius (86 % and 2. moment), beam position, power density distribution, beam propagation factor M2
  • Modes: Single plane measurement, averaging, monitoring
  • Presentation: Isometry, false color, graphical cut, data table.
  • Formats: storage of PRIMES *.foc files or ASCII

BeamMonitor Options

  • Measuring at a fix y-position


Control and presentation

Control is realized by different user specific solutions such as: graphical user interfaces in Microsoft WINDOWSTM availiable as well as a direct connection to a SPC.For interface to a PC or SPC, the built in RS485- interface is used.The software has the following features:

  • Measurement parameters: beam radius (based on 86 % and 2nd moment calculation), beam position and power density calculated from a given power value in peak and 86 % - radius.
  • Measuring modes: single and serial measurement, temporal development
  • Presentation: Isometry, false color, contour lines and check of symmetry.

Compact Laser Profiler

The CameraMonitor 10.6 is a camera-based measuring system analyzing IR laser radiation at 10,6 µm wavelength.

  • fast and convenient
  • easy handling
  • practical design

Application

The new reference system for raw beam diagnostics of CO2 -Lasers is available now.

The BeamMonitor HQ terminates the era of “mode” burns in acrylic glass.
The new beam profiler enables fast high performance measurement with high accuracy. This is ensured by a high dynamics detector system.

Technical description

Measured Beam Parameter

•    Beam position
•    Beam dimensions
•    Beam symmetry

Modes of Operation

  • Service operation


The system is operated by a PC. In this case, it is possible to visualize the complete power density distribution.
The repetition rate of the measurement is limited mainly by the data transmission. With Ethernet-based communication a maximum repetition rate of 0.5 Hz is possible.

  • Remote operation


The BeamMonitor HQ is designed to run via different interfaces by the SPC of the laser machine. All the calculated beam parameters are available. This enables a direct monitoring of all beam parameters.

Technical data

Mechanics

50 mm aperture:
H x B x D:  183 mm x 138.5 mm x 63 mm (without connectors)

Weight:    1.5 kg

Interfaces

•    Ethernet (TCP/IP) DHCP
•    RS 485 / RS 232 - optional

Power supply

•    24 V and maximum 1 A

Maximum acceleration
(device not in operation):  4 g.
During operation no external force should be applied to the device.

The option LineScan enables the operation of the BeamMonitor HQ at a fix y-position. Then, single traces can be measured with a repetition rate up to 30 Hz.

Control and presentation

The BeamMonitor HQ is the perfect tool for the characterization of your laser beam. Its applications reach from monitoring during production to beam profiling during the adjustment of a laser resonator.

The mechanically-scanning system measures the spatial power density of collimated CO2-laser beams at full power.
Due to its compact design and low weight, the BeamMonitor HQ is optimized for service and machine integration.