Effect of temperature change in microholographic recording

In microholographic recording, temperature change causes the thickness and refractive index change of the recording medium, which lead to the decrease in the diffraction efficiency of a microhologram due to the Bragg mismatch. Therefore, the effect of the temperature change in the microholographic recording and its compensation method were investigated through a numerical simulation. The wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. The thickness change ratio and refractive index change of the recording medium due to the temperature change were 5.0×10-4 / deg. and -3.0×10-4 / deg., respectively. The diffraction efficiency of the microhologram was calculated using the coupled wave theory. The tolerance of the temperature change increased from ±1.8 deg. to ±12 deg. with the compensation by the wavelength change of the laser. However, the width of the readout signal after the compensation increased with the temperature change in both the in-plane and vertical directions. In the microholographic recording, the beam consists of multiple plane waves and the microhologram consists of multiple diffraction gratings. At the center of the beam, the corresponding wave vector of the plane wave and grating vector of the diffraction grating are perpendicular to the recording medium. On the other hand, at the periphery of the beam, they are slanted to the recording medium. Therefore, the Bragg matching conditions at the center and periphery of the beam are different from each other. The above results are attributed to this fact.