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For more than 50 years, phase-shifting interferometry has been the technology of choice for high-precision surface form metrology instruments. These interferometers provide fast and reliable measurements of surface form error and transmitted wavefront of optical components, systems, and assemblies. From research environments to a wide range of industrial applications, laser interferometers offer high levels of data traceability for quality assurance and post-production analysis. They have become an integral part of the manufacturing process.

Zygo’s Qualifire represents a leap forward for laser interferometers by providing solutions to known challenges for instruments of this type.

A New Approach to Phase Shifting Interferometry

Common to optical metrology in many modern systems, the Fizeau design uses a fixed, on-axis coherent point source to illuminate the interferometric cavity. For the most part, it works very well. While phase-shifting and fixed illumination remain the gold standard, Zygo is always looking for improvements and has explored the benefits of dynamic illumination with the new Flying Spot option.

The Qualifire laser interferometer offers many novel, new features:

  • Coherent Artifact Reduction – A Qualifire system with the Flying Spot Module installed gives a level of confidence not seen 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. A Qualifire system with a Flying Spot Module enabled 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 the highest resolution instruments on the market, a precise focus on the surface under test must be achieved. 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. In fact, precise focus can be achieved without operator intervention.

  • Stable Zoom – This novel zoom method provides a stable optical alignment so that there is no shift in focus or image centering from 1X to 3X zoom. Because the optical system is diffraction-limited at all zooms, the Instrument Transfer Function (ITF) is also greatly improved making it easier to quantify mid-to-high spatial frequency features. Because 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.

  • Smart Accessories – Using a Zygo Smart Accessory enables Smart Setup features. Smart Setup automatically sets the instrument lateral resolution based on the accessory installed and, for Smart Transmission Spheres, the radius of curvature of the part. Then, an on-board factory calibrated system error map is automatically fit and subtracted from measured data, enabling the best metrology on the market with a reduced setup time.

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) making this instrument much easier to move—which is especially helpful when the test part cannot be brought to the instrument.

Another weight and spacing advantage is an internal Phase Measuring Receptacle (PMR). This eliminates potential damage to the PZT stacks inside the PMR when the unit is moved. Other improvements include easy-grasp handles and a convenient, easy-to-access On/Off switch.

In addition, the optical leg is sealed, providing additional protection for dust that accumulates over time and can add to artifacts in the system. This layout also makes service easier. Even the laser can be changed without disturbing any of the optical components.

Every facet of the trusted Zygo Verifire has been rethought with user experience and confidence in metrology in mind to bring you the new Qualifire product line.