As the demands of high repetition rate, high intensity laser applications rise, robust interference coatings are needed that can balance the conflicting requirements of a strong laser damage threshold, high reflectivity/transmissivity, and low group delay dispersion. Two layer anti-reflection coatings (Air/SiO2/HfSiO/substrate vs Air/SiO2/Hf-SiO2 nanolaminates/substrate) were tested with p-polarized, 77-fs 1030-nm laser pulses. Both coatings had identical refractive index at 1030-nm for the high index layers, but one coating contained a ~200-nm thick layer of mixed HfO2 and SiO2, while the other had a nanolaminate featuring 25 pairs of <5-nm HfO2 and SiO2 layers. Nanolaminate performance under femtosecond irradiation is relatively unexplored; this work aims to address that, and shows the damage threshold fluence of the nanolaminate sample was ~2/3 of that of the mixed layer sample. These results set the stage for developing stronger nanolaminates for femtosecond pulses.
Few temperature-dependent experiments exist for laser damage studies, yet temperature greatly influences material behavior and response to laser irradiation. This study examines the effects of cryogenic temperatures on femtosecond laser-induced damage of copper, chosen for its well-defined thermal properties. Using a 77fs, 1030nm laser at normal incidence, we tested single crystal copper at temperatures ranging from 20K to 350K, in vacuum in a cryostat. Results indicate that lower temperatures increase damage thresholds by 20% from 300K to 25K. Optical and Atomic Force Microscopy reveal underlying mechanisms, complemented by modeling. This research furthers understanding of laser damage physics and strategies to enhance optical damage thresholds in high-power laser systems.
We investigate the unique surface fractures of CaF2 found after single shot laser irradiation using 77 femtosecond, 1030 nm laser pulses. Optical microscopy and atomic force microscopy revealed elevated rectangular structures across laser-ablated craters. The underlying mechanism for this unique morphology may be related to anisotropic thermal conductivity and laser-induced defects. Our findings provide insights into the fundamental mechanisms of laser-induced damage in CaF2 and have implications for the design and optimization of high-power laser systems.
Glass drilling and cutting is crucial for optics, consumer electronics, and Micro-Electro-Mechanical System (MEMS) devices. Speed and reproducibility are issues common to traditional glass cutting methods. We use a femtosecond laser to efficiently and accurately cut interior shapes in glass. Unlike a traditional Gaussian beam, which has a shallow focal range and cannot penetrate deep into materials, Bessel beams have a much longer focal range, up to millimeters. With a Bessel beam, we can cut straight through without the need for mechanical cleaving or moving the sample through the focus, improving reproducibility and speed. The cut surfaces are analyzed with optical microscopy, atomic force microscopy, and scanning electron microscopy to observe any structural/morphological changes to the materials near the laser affected regions. Our 260fs laser operates at 10kHz, with 1030nm central wavelength, depositing 1.4W on target. An axicon generates the Bessel beam with a FWHM central spot size of 6±1µm and a fluence of up to 41Jcm-2. Our study has the potential to open new technological pathways for integrated electronic and photonic platforms.
Understanding the physical mechanism behind the laser-induced damage of multilayer dielectric interference coatings is essential for developing ultra-high intensity laser systems. The previous work reported high damage thresholds of MLD mirrors and blister formation near the threshold. Here, we present the cross-sectional study of the blisters using transmission electron microscopy and focused ion-beam processing. The measurement shows evidence of void formation and phase transformation under the surface, interdiffusion, and intermixing at the interfaces. These findings provide valuable insights into the mechanisms behind laser-induced damage, facilitating the development of more robust and reliable optics for high-power laser applications.
Ultrafast lasers are very useful for surface engineering of semiconductors. Here we used a Scanning Tunneling Microscope (STM) to map in situ topography and spectra of hydrofluoric acid-etched silicon (100) damaged by an ultrafast pulsed Yb:KGW laser at 1030nm with 70fs duration in high vacuum. We observed absence and presence of laser induced periodic surface structures with single and multiple shot irradiation, respectively. Surface morphology were captured with atomic resolution, which can help understand the subtle changes to surface ultrafast lasers can cause near the laser induced damage threshold fluence. The results demonstrate the potential of STM for in-situ studies of laser damage on clean surfaces in ultra-high vacuum.
Cathodoluminescence and electrostatic techniques were used to study the nanoscale spatial evolution of native defects, crystallinity and work function in Ga2O3 across different morphological regions in laser induced periodic surface structures generated by an ultrafast laser. An emergent ~2.4 eV emission, likely related to oxygen interstitials or divacancy complexes, inversely correlates with the crystallinity of these regions. A contrast in work functions between the rims and troughs of the LIPSS, indicative of periodic differences in defect concentration, correlates with a reduction of crystallinity in the rim region relative to the trough region, suggesting an increased concentration of relatively shallow defects.
Understanding the physical process behind laser-induced damage of multilayer dielectric (MLD) interference coatings (IC) is of supreme importance for building ultrahigh-intensity laser systems. We experimentally studied the S-on-1 laser-induced damage threshold (LIDT) and damage characteristics of the SiO2/HfO2 high reflector quarter-wave stacks for three different femtosecond pulse durations operating at 1030nm wavelength. The S-on-1 LIDT for 1,10,100,1000 and 10000 pulses were recorded, and the values compare well with the state of the art. A strong correlation between single-shot damage morphology and laser focal intensity profiles was observed. Potential damage mechanisms of IC layers consistent with our observation will be discussed.
Ultrafast dynamics of ultrashort single pulse induced micro-explosions in bulk Diamond was examined using time resolved shadowgraphy technique in a pump-probe experimental setup. Experimental and theoretical considerations identify such confined micro-explosions creating Warm Dense Matter (WDM) state. Different phases of the ongoing micro-explosions have been captured in real-time with femtoseconds to picoseconds temporal and micron-sized spatial resolutions. This study broadens the horizon of our understanding of exotic matter generation process in extreme environments.
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.