A tunable optical filter

We present the details of a new tunable optical filter, suitable for selecting different bands of wavelength in the UV, visible and IR regions. The filter comprises a ferrofluid-based emulsion cell (emulsion sandwiched between two transparent sheets), a miniature solenoid and a variable direct current source for changing the magnetic field inside the solenoid. By varying the magnetic field, one can tune the filter and select the desired wavelength. We discuss the working principle of the new tunable optical filter with a few examples.