Measuring through Obstacles with Confocal Optics

Problem

In optical interferometry, stray reflections from surfaces such as windows or nearby components can distort measurements, especially in micro-mechanical systems or through layered structures. Standard setups struggle to isolate the signal from the true measurement point.

Solution

The PICOSCALE Vibrometer uses a confocal optical design with a 1550 nm laser and single-mode fiber as a spatial filter. This allows detection of light only from the focal plane, strongly suppressing background signals caused by off-focus reflections—even through vibrating windows or obstructed views.

Implementation

• A titanium sample oscillating at 1 kHz was measured through a glass window vibrating at 240 Hz.

• Three sensor heads were tested (C01, F01, PICOSCALE Vibrometer) to compare background suppression.

• A multi-layered AFM cantilever sample was assembled to evaluate imaging through obstructive geometries.

Results

• The standard PICOSCALE Vibrometer head reduced background vibration from the glass by up to 48 dB (250×), clearly separating the sample signal.

• Confocal imaging successfully resolved both obstructed layers in the multi-layer cantilever structure, and vibrations of each layer could be independently measured.

• The signal-to-noise ratio improved significantly with shorter focal length sensor heads.

Conclusion

Confocal optics in SmarAct’s PICOSCALE systems allow precise imaging and vibration measurement through reflective or obstructive elements, outperforming standard optics in complex or layered setups. This makes it ideal for analyzing enclosed MEMS, sealed microstructures, or systems with optical barriers.