Two-wavelength dynamic interferometer for measuring roughness

We present a method for measuring surface roughness of 2μm RMS and below in a single camera frame acquisition. The interferometer employs two camera sensors with pixelated phase-masked detector arrays. Each camera uses a different wavelength of light to facilitate a two-wavelength dynamic interferometric measurement. The large effective wavelength derived from the two wavelengths enables phase unwrapping over surface roughness steps that visible light typically cannot handle. This allows for the instantaneous measurement of traditionally challenging surfaces, such as machined, ground, or sandblasted metal, using a single camera frame acquisition.