Expansion of axial dispersion in a photopolymer-based holographic lens and its improvement for measuring displacement.

Coaxial multiple holographic lenses as high-dispersion elements are developed for a spectral confocal displacement measurement device. Wavelength and coaxial spatial multiplexing methods are used to record the holographic lens with two coaxial foci. The expansion of axial spatial dispersion in photopolymer-based multiple holographic lenses has been demonstrated and studied experimentally. The multiple holographic lenses provide a larger spatial dispersion to improve the characteristic parameters for measuring the displacement. Compared to single holographic lenses, the maximum of axial dispersion wavelength difference of the multiple lenses increases from 134.63 to 162.81 nm, and the corresponding measurable range increases from 203 to 385 mm. The axial spatial dispersion conforms to a typical exponential function. The overall spatial position sensitivity of multiple holographic lenses reaches 2.36 mm/nm. In addition, the multiple lenses also decrease the lateral dispersion compared to the single lenses. The multiple lenses can efficiently reduce the transverse measurement error. Finally, the displacement measurement result confirms the improvement of measureable spatial range. The multiple holographic lenses can accelerate the practical application of holographic lens-based optical elements.