Relatively thick (>1-um) organic-polymer coatings with a large resistance to laser-induced damage at UV wavelengths are desired for new inertial confinement fusion laser optics under development at the Laboratory for Laser Energetics. These optics include surface-figured, KDP polarization rotators and actively cooled laser glass. Organic-polymer materials, however, are generally known to have a low laser-induced–damage threshold (LIDT) in the UV, particularly as it pertains to multipulse applications. In this work, we present the single-pulse and multipulse LIDT results for thick (>1.5-um) polymethacrylate films deposited on fused silica and cured at different temperatures. The results demonstrate that it is possible for thick polymer films to withstand thousands of pulses at fluences higher than their single-pulse LIDT counterpart. In fact, in some test sites, the underlying fused silica substrate suffered exit surface damage before the polymer film could be damaged. These results and a discussion of the underlying mechanisms responsible for this behavior will be presented.
Polarization smoothing is an important method used to improve beam uniformity and on-target energy coupling during inertial confinement fusion experiments. First-generation polarization smoothing optics deployed in the ultraviolet section of the 60-beam OMEGA Laser System are based on potassium dihydrogen phosphate (KDP) wedges, which produce two diverging, orthogonally polarized beams. An upgrade to a random continuous polarizer (RCP) wave plate is desired that calls for an arbitrary distribution of polarization states. Imprinting a freeform depth profile into a birefringent crystal such as KDP is a promising approach for fabrication of a large-aperture RCP. Modern optical fabrication technologies are capable of imprinting these designs; however, the challenging material properties of KDP require new innovations in process and slurry chemistry. This presentation will discuss recent advances in our efforts to fabricate a KDP-RCP.
Our study analyzed the laser-damage threshold of liquid crystal alignment materials, including photoaligned azobenzene, rubbed polyimide, and rubbed nylon. We found that the presence of liquid crystal was necessary to observe variation in damage thresholds among alignment materials. Nylon outperformed photoalignment, which outperformed polyimide. We also investigated the polarization dependence of the damage threshold in ordinary and extraordinary modes at a near-infrared wavelength and found that only the photoalignment material demonstrated polarization sensitivity at our statistical power level. Our results can inform the design of high-power beam-shaping devices for various applications, including fusion, 3-D printing, and defense systems.
Polarization smoothing of the 3w beam is highly desirable for direct-drive inertial confinement fusion experiments. However, fabrication methods of large-aperture optics that provide “randomized” beam polarization on the target are limited in-part to the challenging nature of the optical materials with suitable birefringence values. We report on the development of two new polarization-smoothing optics by separate and distinctly different approaches. In the first approach, a nematic liquid crystal with a high laser-induced–damage threshold is aligned between two fused silica substrates, with one substrate possessing a freeform, contoured imprint. In the second approach, freeform surface imprinting of potassium dihydrogen phosphate crystals is accomplished by fluid jet polishing.
We investigate fluid jet polishing (FJP) for its potential to be used for freeform finishing of fused silica and potassium dihydrogen phosphate (KDP and DKDP) crystals without compromising laser damage performance. As part of this effort, a different slurry for each material was utilized. Samples with different amounts of material removed by FJP were prepared for damage testing. The results show that FJP can improve or maintain the laser damage resistance of these materials while simultaneously functioning as a deterministic, sub-aperture finishing method.
Deterministic finishing methods of optical components for high-peak-power laser applications that can meet the requirements for high laser damage resistance are not sufficiently developed to meet all needs. This is especially in the case for ultraviolet (UV) laser applications. Fused silica is the material of choice for optics operating at UV wavelengths owing to its intrinsically large bandgap, high transparency, and excellent uniformity. Here, we report on the laser damage behavior of fused silica surfaces finished by fluid jet polishing (FJP) as a function of removal depth. Fused silica test substrates were processed by FJP to depths ranging from 0.7 to 18 μm. Laser damage testing was conducted on these surfaces at 351 nm and 1-ns pulse lengths for both, 1-on-1 and R-on-1 testing protocols. The results for 1-on-1 testing showed no degradation in the laser-induced damage threshold (LIDT) of the substrates. Instead, a gradual improvement starting at a depth of 2.1 μm was observed and continued to the 18 μm surface. At 18 μm of removal, the LIDT was 16% higher than a surface that was not finished by FJP. For R-on-1 testing, all surfaces treated by FJP demonstrated an improvement in laser damage resistance. At depths greater than 5 μm, the improvements were significantly more pronounced and a 30% increase in the LIDT was realized.
Interactions of liquid crystals (LC’s) with polarized light have been studied widely and have spawned numerous device applications across wide regions of the electromagnetic spectrum. To date, little is known about the effect of incident light polarization state on laser-induced damage thresholds (LIDT) for LC’s exposed to high-peak-power, nanosecond-pulsed lasers. This work describes the LIDT dependence on incident polarization for light encountering a LC mesophase in a high degree of molecular orientation. In one example chiral nematic LC, the 1053 nm, 1.4 ns LIDT ranged from 17.7-30.5 J/cm2 in the same device, depending on the input polarization handedness and ellipticity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.