Novel transmission gratings with large angular dispersion, high efficiency and wide spectral bandwidth

Transmission gratings can be placed near the collimator or camera (imaging) optical system, allowing the instruments to be made smaller. We are developing fabrication methods of a volume binary (VB) grating, trapezoid grating and reflector facet transmission (RFT) grating. The VB grating can achieve a larger angular dispersion and higher diffraction efficiency than conventional surface-relief transmission gratings with step shaped grooves, and can be achieved a wider spectral bandwidth than volume phase holographic (VPH) gratings whose refractive index is sinusoidally modulated. The trapezoid grating can bring the spectral characteristics of s- and p-polarization closer to each other than a VB grating, so it can further improve the peak diffraction efficiency. The RFT grating is a new transmission type echelle grating in which the incident light on one side facet of the sharp sawtooth-shaped grating is reflected on the other side facet, and the diffracted light is emitted from the plane on the back side of the grating. The RFT grating has higher diffraction efficiency and wider spectral bandwidth than a conventional reflection echelle grating.