### STP689: Simplified Description of Dielectric Reflectors

Sparks, M.

*Xonics, Incorporated Santa Monica, California*

Flannery, M.

*Xonics, Incorporated Santa Monica, California*

Pages: 10 Published: Jan 1979

**Abstract**

The spectral reflectance, R(ω), of a quarter-wave reflector is quite asymmetric in general as a result of absorption. The maximum electric field E in an infinite stack is in the center of the high-index (low-index) layer at the low-frequency (high-frequency) end of the high-reflection band. Thus, the absorptance minimum of a stack having much greater absorption in the high-index material occurs at ω> ω^{c} (band center). Operation at ω> ω^{c} could increase the damage resistance if the high-index material is easily damaged. At ω^{c}, E decays rapidly. As ω departs from ω^{c} in an infinite reflector, E penetrates deeper into the coating, with no decay at the band edges. The peak-to-peak distance in an __infinite__ dielectric stack is constant for all frequencies in the band. By using the continuity of E and dE/dz, E can be obtained from E= 0 at the metallic substrate or, in an infinite stack, from E=0 at the reflector surface for ω = ω^{C} or E=0 in the center of the high- or lowindex layer at the band edges. Simple closed-form approximations for the spectral absorptance and the phase of E are accurate and sufficient for present applications.

**Keywords:**

Dielectric reflectors, spectral absorptance, reflectance, electricfield distribution, theory, asymmetric absorptance, high-power, damage thresholds

**Paper ID:** STP39126S

**Committee/Subcommittee:** F01.02

**DOI:** 10.1520/STP39126S

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