Multicolor Photoluminescence from Porous Silicon Using Focused, High‐Energy Helium Ions

–2 intensity. During photoirradiation, we monitored the optical texture of the blue phases with a polarizing optical microscope. Optical experiments were conducted with an optical microscope (IX71, Olympus) combined with spectrometers (USB2000, Ocean Optics). We focused the non-polarized white-light beam from a tungsten halogen light source (L7893, Hamamatsu Photonics) on the surface of the sample with a spot size of 30 lm in diameter through an objective (50, LC Plan Apo, Olympus). The spontaneous emission spectra from the blue phases were measured by using a continuouswave (CW) laser (532 nm, 0.13 mW, Edmund Optics), and lasing spectra were measured by a Q-switched Nd:YAG (yttrium aluminum garnet) laser (532 nm, 8 ns pulse, Polaris II, New Wave Research). The excitation energy was adjusted using a half-wave plate in combination with a polarizing prism. The excitation beam was conducted to the optical microscope and focused onto the sample surface through an objective (20, LC Plan Apo, Olympus) to obtain a spot size of about 50 lm. We collected the laser emission from the sample in transmission and analyzed the spectrum with a spectrometer (Spectra Pro. 150 and charge-coupled device (CCD) detector 256HB, Acton Research).

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