Multidie LED combined with homogenizing optics to improve frequency response and intensity for FLIM applications.

Application of light-emitting diodes (LEDs) in frequency-domain fluorescence lifetime imaging microscopy (FLIM) has been limited by the trade-off between modulation frequency and illumination intensity of LEDs, which affects the signal-to-noise ratio in fluorescence lifetime measurements. To increase modulation frequency without sacrificing output power of LEDs, we propose to use LEDs with multiple dice connected in series. The LED capacitance was reduced with series connection; therefore, the frequency response of multidie LED was significantly increased. LEDs in visible light, including blue, green, amber and red, were all applicable in FLIM. We also present a homogenizing optics design, so that multidie LEDs produced uniform illumination on the same focal spot. When the homogenizing optics was combined with multicolour emitters, it provides multiple colour selection in a compact and convenient design.