Tiny Gold Sensors That Beat Light Into Heat Signals

A new study shows that gold films only a few nanometers thick can be turned into tiny mechanical sensors. These devices vibrate at very high frequencies, in the range of millions of cycles per second. When a laser shines on them, their vibration frequency shifts in a predictable way, allowing the sensor to act like a tiny thermometer for light energy. The researchers measured how much the vibration frequency changes per unit of absorbed power. They found a responsivity around eleven parts‑per‑million per microwatt, which is surprisingly high for such small structures. Moreover, the devices kept their performance steady over a wide range of laser powers, from just a few microwatts up to almost half a milliwatt.The sensor’s behavior is very linear. The non‑linearity factor, which tells how much the response deviates from a straight line, was only 0. 0865. This means that the device can reliably translate light power into frequency changes without needing complex calibration. By studying how the vibration frequency scales with size, the team extracted material properties of the ultrathin gold. The Young’s modulus came out to about 75. 6 gigapascals, close to values for bulk gold, while the pretension in the membranes ranged from 0. 09 to 0. 8 newtons per meter. These findings open the door to building large arrays of such sensors on a single chip. Because they are so thin and mechanically simple, they could be integrated into photonic circuits or used to monitor light intensity in compact devices. The work also demonstrates that adding mechanical motion to ultrathin metal films adds a powerful new dimension to their sensing abilities.