Figure 4.3.

Principle of the OIRD method.

First, a p-polarized He-Ne laser beam (λ = 632.8 nM) passes through a photoelastic modulator to induce oscillation between p- and s-polarization at a frequency of 50 kHz. Second, after passing through a phase shifter, the resultant beam is incident on the microarray surface at an oblique angle theta (θ_inc). Finally, the first I(Ω) and second harmonics I(2Ω) of the reflected beam intensity are simultaneously monitored by two digital lock-in amplifiers.