A Dynamic Strategy for Wavelength Sensing Using the Diffracted Orders of a Grating.

We propose a strategy for real time multicolour detection of light emitting particles under flow conditions, using the diffracted orders of a grating. The method relies on the fact that the spatial (angular/linear) separation between the orders of a diffraction grating is a wavelength dependent quantity. Thus, the difference in arrival times at a fixed detector for neighbouring orders produced by a moving, light-emitting particle can be used as a wavelength sensing mechanism. We demonstrate this functionality using a prototype PDMS microfluidic device that incorporates a focusing transmission grating. A key attribute of this approach is that it requires only a single sensitive detector, such as a photomultiplier tube, in contrast to many conventional approaches which require multiple sensitive detectors or a detector array.