| 摘要 |
A hologram optical element having a thin form and a high degree of light transmittance, moreover that provides superior handling ease, as well as a surface light source device employing this hologram optical element. The angle at which light can be bent in this hologram optical element, has low wavelength dependency, and the hologram optical element enables prevention of spectral separation in white light incident from an oblique direction which is bent to a vertical direction and emitted. A transmitting diffraction grating, when light of wavelengths lambda1, lambda2 and lambda3 within the ranges 0.46<=lambda1<=0.50 mum (blue light), 0.53<=lambda2<=0.57 mum (green light), 0.60<=lambda3<=0.64 mum (red light) is incident at angle thetai, the maximum diffraction angle for diffractive efficiency of each wavelength is within the range from -5 degrees to +5 degrees.
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