High-efficiency multiwavelength beam expander employing dielectric-enhanced mirrors

A high-efficiency beam-expander optical system for use at ultraviolet (UV), visible (VIS) and infrared (IR) operating wavelengths, comprising:

• a first mirror with a convex substrate surface formed on a first Al alloy substrate and a second mirror with a concave substrate surface formed on a second Al alloy substrate, with the first and second mirrors arranged in an off-axis, afocal configuration having greater than unity magnification;
• wherein the convex and concave substrate surfaces each includes a multilayer reflective coating formed from alternating layers of HfO2 and SiO2 having respective layer thicknesses τH and τS;
• wherein each multilayer reflective coating includes:
• i) a first section having an SiO2 layer immediately adjacent the convex or concave substrate surface and configured to optimally reflect the IR operating wavelength and substantially transmit a mid-wavelength IR (MWIR) wavelength;
• ii) a second section atop the first section and configured to optimally reflect the VIS operating wavelength and substantially transmit the IR and MWIR operating wavelengths;
• and iii) a third section atop the second section and configured to optimally reflect the UV operating wavelength and substantially transmit the VIS, IR and MWIR wavelengths;
• and
• wherein the respective HfO2 and SiO2 layer thicknesses τH and τs are substantially constant within each section but are smaller in the second section on average than in the first section and in the third section on average than in the second section;
• and
• wherein the beam-expander optical system has an optical transmittance TBE>95% at the UV, the VIS and the IR operating wavelengths.