Shadow Moiré

Flatness Measurement and Analysis Technique

Shadow Moiré is a non-contact, full-field optical technique that uses geometric interference between a reference grating and its shadow on a sample to measure relative vertical displacement at each pixel position in the resulting image. It requires a Ronchi-ruled grating, a white line light source at approximately 45 degrees to the grating and a camera perpendicular to the grating. Its optical configuration is shown in the figure to the right. A technique, known as phase stepping, is applied to shadow moiré to increase measurement resolution and provide automatic ordering of the interference fringes. This technique is implemented by vertically translating the sample relative to the grating

The strengths of the shadow moiré measurement technique include:

• Full field data acquired in less than 2 seconds
• Resolution down to <1 micron
• Resolution is unchanged by field of view
• Highly robust with minimal moving parts

The shadow moiré technique is offered on the following Akrometrix tools:

• AXP
• PS200S
• PS600S
• AKM600P