Analysis of laser damage tests on coatings designed for broad bandwidth high reflection of femtosecond pulses

Abstract

Abstract. We designed an optical coating based on TiO 2 ∕SiO 2 layer pairs for broad bandwidth high reflection (BBHR) at 45-deg angle of incidence (AOI), P polarization of femtosecond (fs) laser pulses of 900-nm center wavelength, and produced the coatings in Sandia's large optics coater by reactive, ion-assisted e-beam evaporation. This paper reports on laser-induced damage threshold (LIDT) tests of these coatings. The broad HR bands of BBHR coatings pose challenges to LIDT tests. An ideal test would be in a vacuum environment appropriate to a high energy, fs-pulse, petawatt-class laser, with pulses identical to its fs pulses. Short of this would be tests over portions of the HR band using nanosecond or sub-picosecond pulses produced by tunable lasers. Such tests could, e.g., sample 10-nm-wide wavelength intervals with center wavelengths tunable over the broad HR band. Alternatively, the coating's HR band could be adjusted by means of wavelength shifts due to changing the AOI of the LIDT tests or due to the coating absorbing moisture under ambient conditions. We had LIDT tests performed on the BBHR coatings at selected AOIs to gain insight into their laser damage properties and analyze how the results of the different LIDT tests compare.

Sandia's Z-Backlighter Laser Facility

“…The chamber uses e-beam deposition with the option of ion-assisted deposition to produce dielectric coating layers. Most optics use coatings consisting of HfO 2 and SiO 2 layers due to their ability to meet our optical and laser damage requirements, although other oxides such as [34][35][36] have also been investigated. Most of the coatings are for anti-reflection (AR) or high reflection (HR) at 1054 nm and 1064 nm or at the second harmonics of 527 nm and 532 nm, with specifications covering a variety of use angles and use environments (typically vacuum or dry air).…”

Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO2, Nb2O5, or Ta2O5high-index layers

“…4 These HfO 2 alternatives will support coatings where a broader high reflection bandwidth is necessary. Examples include mirrors for femtosecond laser pulses, 5,6 accommodating the spectral shift to longer wavelengths of coatings due to water absorption and aging effects (a common problem with e-beam coatings) 7 and providing angle of incidence (AOI) flexibility.…”

Year in Review

“…According to the Web of Science, three were in the laser damage special section, describing laser damage tests for femtosecond laser coatings, 11 laser-induced damage by picosecond pulses on petawatt-class laser coatings, 12 and laser-based removal of space debris. 13 The active electro-optical sensing special section included top-cited papers on hyperentanglement 14 and deep turbulence wavefront sensing, 15 while papers on anisoplanatic imaging through turbulence 9 (the only top-ten downloaded and cited) and atmospheric turbulence mitigation algorithms 16 from the long-range imaging special section were part of the list.…”