Posted in | Laser Interferometers

Qualifire™ Laser Interferometer: New Approach to Phase Shifting Interferometry

Phase-shifting interferometry has been the preferred technology for high-precision surface-form metrology instruments for more than 50 years. These interferometers measure the transmitted wavefront and surface form error of optical assemblies, systems, and components quickly and accurately.

Laser interferometers provide high degrees of data traceability for post-production analysis and quality assurance in a variety of industrial settings as well as research settings. They are now an essential component of the production process.

Zygo’s Qualifire is a major advancement for laser interferometers, providing solutions to known challenges for instruments of this type.

A New Approach to Phase-Shifting Interferometry

As with most modern optical metrology systems, the Fizeau design uses a fixed, on-axis coherent point source to light up the interferometric cavity. For the most part, it works very well. While traditional methods such as phase-shifting and fixed illumination are widely accepted, Zygo maintains a commitment to innovation by continually seeking improvements, and with the new Flying Spot feature, it has investigated the advantages of dynamic illumination.

The Qualifire laser interferometer has a lot of new and innovative features:

  • Flying spot: New coherent artifact reduction technique
  • Stable zoom
  • Plano cavity autofocus
  • Smart accessories 

Qualifire - High Functionality in a Streamlined Design

Qualifire is available with either a 4-inch aperture or a smallest-in-class 6-inch aperture. Some Qualifire versions weigh less than 50 pounds (23 kg), meaning that this instrument is much easier to move—which is especially helpful when the test part cannot be brought to the instrument.

Another benefit in terms of weight and spacing is the inclusion of an internal Phase Measuring Receptacle (PMR). This feature effectively prevents potential damage to the PZT stacks housed within the PMR during unit relocation. Other improvements include a convenient, easy-to-access On/Off switch and easy-grasp handles.

Furthermore, the optical leg is sealed, which offers enhanced protection against dust that accumulates over time, which can exacerbate system artifacts. Furthermore, this layout facilitates easier servicing. Notably, the laser can be replaced without causing any disruption to the optical components.

Every facet of the trusted Zygo Verifire has been thought out, with a focus on enhancing user experience and instilling confidence in metrology. This dedication has culminated in the creation of the new Qualifire product line.

New Key Features:

Coherent Artifact Reduction

A Qualifire system with the Flying Spot Module installed gives users a level of confidence that has never been seen before with other noise reduction systems. By removing coherent spatial noise and annoying coherent bullseye artifacts from the cavity, the Flying Spot gives the best signal to noise for high-precision measurements.

When the Flying Spot Module is enabled, the Qualifire system takes the best of Zygo’s patented Ring of Fire and Coherent Artifact Reduction System (CARS) technologies creating a single noise reduction solution.

Plano Cavity Autofocus

For top-of-the-line instruments boasting the highest resolution available, attaining precise focus on the test surface is imperative. The Flying Spot Module allows for a phase-based autofocus method. This means that a very precise focus can be set on perfectly specular surfaces, without the need for edges, fiducials, reticles, or other physical artifacts necessary for manual or intensity-based focus. Precise focus can be achieved seamlessly without any operator intervention.

Stable Zoom

This new zoom technique offers a stable optical alignment so that there is no shift in focus or image centering from 1X to 3X zoom. Due to the diffraction-limited nature of the optical system across all zoom levels, the Instrument Transfer Function (ITF) sees significant enhancement, simplifying the quantification of mid-to-high spatial frequency features.

As there is no shift in image focus or centering when system magnification is changed, system error subtraction can be maintained for all zooms without loss of fidelity.

Zygo Smart Accessory

Using a Zygo Smart Accessory enables Smart Setup features. Smart Setup autonomously configures the instrument's lateral resolution according to the installed accessory and, for Smart Transmission Spheres, the radius of curvature of the part.

Subsequently, an onboard factory-calibrated system error map is automatically applied and subtracted from the measured data. This streamlined process ensures top-tier metrology performance while significantly reducing setup time.

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