Real-time 1D hyperspectral imaging of porous silicon-based photonic crystals with one-dimensional chemical composition gradients undergoing pore-filling-induced spectral shifts

• New sensor design using imaging spectrometer.
• Real-time 1D hyperspectral imaging of composition gradients.
• Spectral imaging of photonic crystals.
• Spectral imaging of gradient-modified porous silicon.
• Slow filling of porous silicon pores.

A line-scan hyperspectral imager can provide real-time spectral information at many points along a transect of a gradient-modified material. This is demonstrated by monitoring the optical reflectance spectrum of a porous silicon photonic crystal with a hydrophobic/hydrophilic pore-wall surface composition gradient while it is immersed in water to which ethanol is added. The combination of the hyperspectral imager and the pore-wall composition gradient allows a detailed study of the pore filling process. It is observed that even the most hydrophobic pores fill to a small extent when only a small amount of ethanol has been added. This gradient of filling is in contrast to visible observation of the porous silicon samples, which can suggest a step change in pore filling. The pore-filling process can take many minutes when the solution composition allows pores at a given position along the gradient to be about 50% filled. These observations demonstrate the utility of aligning a line-scan hyperspectral imager with a gradient material.