While transmission spectroscopy can be a very powerful technique, high sensitivity will require a long absorption path. In other words, there is a limit to how small you can make a transmission analyzer without compromising on performance. For applications requiring a miniaturized device, we have therefor developed a photo-acoustic spectrometer. In this analyzer we also make use of the fact that many gases absorb infrared light, but instead of measuring the attenuation of transmitted light, we measure the change in pressure resulting from the absorption. This technique is superior with respect to sensitivity per analyzer size.
Photo-acoustic spectroscopy is a fascinating technique illustrated in figure3. Simply put, we tickle the molecules with infrared light and make them hum: As the optical filter scans its peak wavelength in and out of the absorbing spectral range of a target gas, the temperature will oscillate, and in turn result in a periodic change in pressure also known as a sound. This century old technique has been miniaturized by Tunable through the power of an optical microphone fabricated using nano-technology. With our photo-acoustic spectrometer we have created a highly compact, yet sensitive gas analyzer, that fits inside the palm of your hand.