Abstract
The effect of postexposure heat treatment on changes in the spectral and diffraction characteristics of reflection holograms is studied. Holograms are obtained on holographic photopolymer materials with different thickness (8–10 and 20–25 \(\mu\) m) in two cases of post-processing (immediately after completion of their recording and after ultraviolet hardening of the photopolymer). It is found that long-term heat treatment of unhardened holograms with a thickness of 10 \(\mu\) m at 50 \({}^{\circ}\) C leads to an increase in the refractive index modulation amplitude from 0.014 to 0.022. Unhardened holograms are characterized by a significant shift of the spectral response to the short-wavelength range and broadening of its contour due to significant shrinkage of the photopolymer and distortions of the spatial structure of the holographic grating. After hardening, heat treatment does not cause noticeable changes in the spectral and diffraction characteristics of the holograms regardless of their thickness. It is established that heating or cooling of hardened holograms with a thickness of 25 \(\mu\) m in the range of 50–5 \({}^{\circ}\) C leads to a bathochromic or hypsochromic shift of the spectral response of the holograms controlled in real time while the holograms with a thickness of 8 \(\mu\) m are not characterized by such shifts, which leads to the formation of athermolyzed holographic optical elements that are insensitive to temperature changes.
