ModeMaster™ Laser Beam Propagation Analyser

The original M² laser beam propagation analyser for CW lasers 

Coherent's ModeMaster™ is ideal for measuring CW laser divergence, M² (or k) and astigmatism for beam sizes between 0.2 and 25mm for lasers with wavelengths from 220nm to 15μm. ModeMaster determines beam waist location and diameters, including the D4σ diameter and Rayleigh Range, as well as angular and translational beam pointing stability.

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The Latest Model - ModeMaster PC

Coherent pioneered M² beam propagation analysis with the ModeMaster system more than a decade ago. Now, Coherent introduces the ModeMaster PC, the newest version of the ModeMaster line of M² laser beam propagation analysers. The ModeMaster PC retains the ISO-compliant accuracy of the original while assing USB control / interface console and software for operation with the latest Windows based PC computers. The ModeMaster PC is also compatible with all existing ModeMaster systems, allowing current users to easily upgrade their system for use on a supported PC computer.

Easy Beam Alignment

The ModeMaster PC features a precision 5-axis head mount which combined with the beam position display provides for easy angular alignment and translational centering of the ModeMaster lens and scan axis to the beam propagation path.

Second Moment Diameters

Beam diameter is a critical parameter in beam propagation measurements. Second moment diameters (D4σ) give the best theoretical answers for beam propagation calculations. The ModeMaster PC measures second moment diameters directly.The ModeMaster PC software also includes conversion algorithms from its knife-edge measurements to second moment diameter measurements that are valid for stable resonator modes with M² of 1 to 4 (covering most commercially available lasers). Also included are conversions to D86 and slit diameters to allow comparison with other measurements.

Real-Time Power Density Adjustment

In most laser applications, it’s not laser power that does the work, it’s the power density. Using the ModeMaster PC, the point of maximum power density can be quickly located. The ModeMaster PC’s convenient power density tuning screen displays power density as a pseudo analog “tune bar,” giving real-time feedback as the laser mirrors are adjusted.

ModeMaster PC Software & Interface Features

Real-Time M2 and Beam Profiles

The ModeMaster PC provides real-time measurement and display for fine tuning of M² and many other beam propagation parameters, along with the near-field or far-field pinhole intensity beam profiles.

Beam Pointing and Translational Stability

ModeMaster is able to measure and display both translational (parallel to the beam axis) or angular (from a pivot point) beam movement over a period from 2 minutes to 24 hours. The angular pivot point of the beam axis (often a single optical surface) can be located along the beam path. Statistical analysis of the beam axis location and angle are displayed for both the X and Y axes. Three levels of filtering reduce noise and increase the sensitivity of pointing stability measurements.

Expanded On-line Help

The ModeMaster PC provides complete on-line help. Help messages are also displayed when beam parameter limits are exceeded and messages suggest corrective measures.

Upgrading to the ModeMaster PC

All previous versions of the ModeMaster system can be upgraded to the ModeMaster PC by replacing the original console unit and the LabMaster display with the ModeMaster PC control / interface module. The ModeMaster software would also need to be installed in a user-supplied PC computer (see minimum requirements below). All original ModeMaster scan heads are fully compatible and can be plugged into the ModeMaster PC controller, which can be ordered separately and includes the software.

RS-232 Interface

The ModeMaster PC can provide measured beam data, analysis results and focus scan control through the RS232 interface for remote data logging, results monitoring and measurement control.

Minimum Computer Requirements

• MS Windows 98, ME, 2000 or XP
• USB port available
• Laptop or desktop PC with 586 (Pentium II) 233 MHz processor or better
• 64MB of RAM
• 30MB of free hard disk space
• SVGA graphics card and display (800 x 600 recommended)
• Serial communication port (for remote operation)

Selecting a ModeMaster PC System

The ModeMaster PC systems are available in eight standard configurations. These eight configurations provide measurements in four wavelength ranges, with two divergence ranges (high divergence and low divergence) within each wavelength range. Use the following steps, along with the selection chart and configuration table (below), to select a ModeMaster PC configuration. 

Step 1. Choose between the four spectral ranges: UV (220-680nm); VIS (340-1000nm); NIR (800-1800nm); & IR (1.8-15µm).

Step 2. Determine the approximate divergence of your laser beam and use the selection chart below to decide between the high and low divergence ModeMaster models for our chosen wavelength range.

Step 3. Confirm your beam size is <25 mm diameter for the low divergence configuration or <12 mm for the high divergence configuration.

Step 4. Use the table below to determine the selected ModeMaster PC configuration part number and verify that all other beam specifications are suitable for your laser.

Step 5. If you determine that you need more than one ModeMaster scan heads to cover the range of your laser parameters, optional scan head modular components can be ordered to change the configuration of the ModeMaster PC system to cover other ranges.

ModeMaster Standard Configuration Table

Notes:
1) Wavelength-dependent properties are input power and max / min divergence (see also notes 2, 5 & 6).
2) Power levels are proportional to the inverse of the spectral response of the detector. The silicon detector peaks at 900nm and is at half-peak sensitivity at 510nm and 1050nm. The germanium detector peaks at 1500nm and is at half-peak sensitivity at 1100nm and 1650nm. The pyroelectric detector has a flat spectral response.
3) These limits can be reduced by a factor of 10 (higher sensitivity) by user-removal of the light-restricting aperture in front of detector.
4) The maximum divergence limit is fixed by the inability to accurately locate the internal waist when the internal beam diameter growth (over the span of the drum) is too slight. Limits shown are for M2 = 1 and test wavelength; limits scale as the square root of M2 (test wavelength).
5) Minimum divergence in this wavelength range scales as the square root of M2 (test wavelength).
6) Diameters are approximate; divergence takes precedence in choosing options. Refer to selection chart.

ModeMaster Specifications

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