Laser-induced Damage Threshold Measurements Research Articles

Influence of Ambient Humidity on the Performance of Complex Spectral Dielectric Films on SiO2/K9 Substrates

Ambient humidity is an important factor to consider when maintaining dielectric films’ component performance. Herein, humidity-influenced experiments were conducted on complex spectral dielectric films based on SiO2 and K9 substrates. Firstly, complex spectral dielectric films’ spectral and surface stresses in different humidity environments were measured. Subsequently, laser-induced damage threshold measurements were carried out on these components. The experimental results indicate that the environmental humidity will induce the evolution of the internal structure of the dielectric films on the mirror, resulting in the deformation of the coating surface and a slight shift of the reflection spectrum. At the same time, the environmental humidity also greatly influences the anti-laser damage performance of the dielectric film mirror. Dielectric films based on SiO2 have excellent damage resistance in high-humidity environments. Conversely, K9-based dielectric films have better damage resistance in low-humidity environments.

Reduction of nanoparticles in optical thin films through ion etching.

Contaminating particles in optical thin films can lead to the formation of nodules and reduction of laser induced damage threshold (LIDT). This work investigates the suitability of ion etching of the substrates to reduce the impact of nanoparticles. Initial investigations suggest that ion etching can remove nanoparticles from the sample surface; however, doing so introduces texturing to the surface of the substrate. This texturing leads to an increase in optical scattering loss, though LIDT measurements show no significant reduction in the durability of the substrate.

Research on synchronous trigger module of laser-induced damage threshold measurement device

Research on synchronous trigger module of laser-induced damage threshold measurement device

Compact Passively Q-Switched Tm:KY(WO<sub>4</sub>)<sub>2</sub> Laser

Diode-pumped thulium lasers emitting in the spectral range near 2 μm are attractive for applications in different areas: surgery, rangefinding, and environmental atmosphere monitoring. In this article the latest results of Tm:KYW laser performance with a polycrystalline Cr:ZnSe as the most available saturable absorber for 2 μm spectral region are presented.A maximum continuous-wave output power of ≈ 0.65 W with a slope efficiency of 55 % was obtained at the wavelength of 1940 nm. Laser pulses with energy of 26 μJ and repetiotion rate of 6 kHz coresponding to 156 mW of average output power at 1910 nm were obtained at 2.2 W of incident puwp power for the Cr:ZnSe saturable absorber with initial transmission of 95 %. By using of saturable absorber with lower initial transmission of 90 % laser pulses with energy of 40 μJ and duration as short as 10 ns were realized. The maximal pulse repetition rate was 2.8 kHz at incident pump power of 2.2 W.Based on the obtained results, it can be concluded that Tm:KYW crystals are promising active media for the compact passively Q-switched lasers emitting in the spectral range near 2 μm for the usage in surgery and rangefinding. Also, described laser is planned to be used as a laser source in laser-induced damage threshold measurements setup for investigation of damage threshold of saturable absorbers as well as nonlinear crystals at the wavelength near 2 μm.

Pulsed laser-induced damage threshold measurement and damage performance of optical components

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Laser-Induced Damage in Silica Nanofibers in Air and Immersed in Different Liquids in the Nanosecond Regime

Thanks to their unique optical properties, silica nanofibers are used in a growing number of applications. Moreover, the possibility of immerging them in various media adds another interesting feature to these devices. However, as for all optical components, nanofibers are limited by the optical damage that can be induced by a laser. In this Letter, we present for the first time to our knowledge Laser-Induced Damage Threshold (LIDT) measurements of silica nanofibers in air and in three common liquids (ethanol, isopropanol, and water). The experiments were performed in the nanosecond regime with a pump source emitting at the wavelength of 532 nm. Different nanofiber radii (from 220 nm to 450 nm) and two nanofiber lengths (2 cm and 8 cm) were tested. We firstly present the experimental setup and protocol. A significant number of samples were realized, and the results were highly repeatable. We also showed that immerging a nanofiber in a liquid substantially enhanced the LIDT, the most important increase having been obtained for nanofibers immersed in water for which the LIDT energy was almost multiplied by a factor of 2 compared with air ( 0.38 μJ in air vs 0.71 μJ in water for a radius of 350 nm). This property offers a new degree of freedom to widen the field of applications of nanofibers, where high peak powers are needed.

Crystallization behavior of ion beam sputtered HfO2 thin films and its effect on the laser-induced damage threshold

In this work, we present our results about the thermal crystallization of ion beam sputtered hafnia on 0001 SiO2 substrates and its effect on the laser-induced damage threshold (LIDT). The crystallization process was studied using in-situ X-ray diffractometry. We determined an activation energy for crystallization of 2.6 ± 0.5 eV. It was found that the growth of the crystallites follows a two-dimensional growth mode. This, in combination with the high activation energy, leads to an apparent layer thickness-dependent crystallization temperature. LIDT measurements @355 nm on thermally treated 3 quarter-wave thick hafnia layers show a decrement of the 0% LIDT for 1 h @773 K treatment. Thermal treatment for 5 h leads to a significant increment of the LIDT values.

Growth and characterization of organic nonlinear optical material: hemikis (piperazine) 4-hydroxybenzoic acid monohydrate single crystal

Hemikis (piperazine) 4-hydroxybenzoic acid monohydrate (P4HBA) was successfully synthesized, and single crystal was grown by slow evaporation solution growth technique. It crystallized in monoclinic system with centrosymmetric space group P21/c. The grown crystal was characterized by powder X-ray diffraction analysis. High-resolution X-ray diffraction rocking curve was recorded to assess the perfection of the grown crystal. UV–visible and photoluminescence studies were performed to explore its optical transmission and emission properties, respectively. Thermal stability and decomposition of P4HBA was illustrated through TG/DSC analysis. The laser-induced damage threshold measurements were performed by using Nd:YAG laser. Third-order nonlinear optical parameters of P4HBA crystal were estimated by Z-scan technique using He–Ne laser of wavelength 632.8 nm.

Laser-induced damage thresholds of ultrathin targets and their constraint on laser contrast in laser-driven ion acceleration experiments

Abstract Single-shot laser-induced damage threshold (LIDT) measurements of multi-type free-standing ultrathin foils were performed in a vacuum environment for 800 nm laser pulses with durations τ ranging from 50 fs to 200 ps. The results show that the laser damage threshold fluences (DTFs) of the ultrathin foils are significantly lower than those of corresponding bulk materials. Wide band gap dielectric targets such as SiN and formvar have larger DTFs than semiconductive and conductive targets by 1–3 orders of magnitude depending on the pulse duration. The damage mechanisms for different types of targets are studied. Based on the measurement, the constrain of the LIDTs on the laser contrast is discussed.

Optical damage thresholds of microstructures made by laser three-dimensional nanolithography

Direct laser writing based on non-linear three-dimensional nanolithography (also known as 3D laser lithography, 3DLL) is a powerful technology to manufacture polymeric micro-optical components. However, practical applications of these elements are limited due to the lack of knowledge about their optical resilience and durability. In this Letter, we employ 3DLL for the fabrication of bulk (i.e., fully filled) and woodpile structures out of different photopolymers. We then characterize them using the S-on-1 laser-induced damage threshold (LIDT) measurements. In this way, quantitative data of LIDT values can be collected. Furthermore, this method permits to gather damage morphologies. The results presented demonstrate that LIDT values depend on the material and the geometry of the structure. Bulk non-photosensitized hybrid organic/inorganic photopolymer SZ2080 structures are found to be the most resilient with a damage threshold being 169 ± 15 m J / c m 2 .

Preparation and characterization of Tb1-xNdxVO4 single crystals for optical isolators

High optical quality Tb1-xNdxVO4 (TNV) single crystal with dimensions of Ø29 × 39 mm3 was grown by the Czochralski (Cz) technique. Powder X-ray diffraction analysis was performed, indicating that as-grown crystal belongs to tetragonal system. The optical and magneto-optical properties have been investigated in detail. TNV possesses very high transmittance, especially in the near-infrared region. The Verdet constant of TNV at 1064 nm reaches 71 rad m−1T−1, 78% larger than that of reference compound TGG. The high magneto-optical figure of merit and extinction ratio also reveal the superior magneto-optical performances of TNV in comparison with TGG. Measurements of thermal conductivity and laser-induced damage threshold (LIDT) were also carried out. These features make Tb1-xNdxVO4 a potential candidate for magneto-optical applications in the near-infrared (NIR) region.

Electric-field intensity enhancement of a series of artificial nodules in a broadband high-reflection coating

A broadband high-reflection (HR) coating was used to suppress the electric-field intensity (EFI) enhancement in artificial nodules with five different sizes. However, the finitie-difference time-domain simulations reflected that the nodules initiating from 1.0-μmSiO2 seeds showed abnormally stronger EFI enhancement, which is almost two times higher than the EFI enhancement of 1.0-μmSiO2 seeds in a quarter-wave HR coating. This was also confirmed by the laser-induced damage threshold measurement. Our previous model combining light focusing and light penetrating effects was carefully examined to check whether the hotspots in a nodule initiating from the 1.0-μmSiO2 seed were in the focal area or not. Although it was found that the focal length of the nodule decreased with reducing seed diameter, the hotspots in nodules initiating from a 1.0-μmSiO2 seed were still much shallower than the focal area. In the broadband HR coating, the standing-wave EFI profiles at different working angles were given, which showed that the standing-wave EFI at the hotspots region was not negligible. Some complex interference or diffraction may cause the light to arrive at the hotspots region in phase and result in strong EFI enhancement. More work is necessary to gain a deeper understanding of this phenomenon.

Investigation of laser induced damage threshold measurement with single-shot on thin films

A method for rapid determination of laser induced damage threshold (LIDT) of optical coatings is proposed and investigated in this paper. By use of this method, the LIDT of thin film can be rapidly obtained by only one shot. The modulation of laser beam profile, which is considered as a negative factor in conventional LIDT test, is utilized in this method. Basing on image processing technique, the damage information could be extracted from the comparison between the damage pattern and beam intensity distribution in the test region. The applicability and repeatability of this testing method has been verified on three type reflectors, HfO2/SiO2, HfO2/Al2O3 and Ta2O5/SiO2. In addition, the experimental results showed that appropriate beam size, laser energy and image compression ratio are the key factors to ensure a high accuracy of LIDT.

Comparative LIDT measurements of optical components for high-energy HiLASE lasers

Further advancement of high-energy pulsed lasers requires a parallel development of appropriate optical components. Several different optical components, such as mirrors and antireflection-coated windows, which are essential for the design of HiLASE high average power lasers were tested. The following paper summarizes results on the measurements of laser-induced damage threshold of such components, and clearly shows their capabilities and limitations for such a demanding application.

Dual wavelength laser-induced damage threshold measurements of alumina/silica and hafnia/silica ultraviolet antireflective coatings.

An approach for the measurement of the laser-induced damage threshold with two wavelengths combined was made while testing antireflective coatings for the wavelengths 266 and 532 nm. Samples were made of Al2O3/SiO2 and HfO2/SiO2 ion beam sputtered films. The results show that adding radiation of a second wavelength might lead to a significant reduction of the threshold. The damage morphology of single and dual wavelength tests is very similar and does not suggest an altered damage mechanism. Further investigations indicated that the dual wavelength threshold is a function of the temporal delay of the two pulses.

Nanosecond laser induced damage thresholds in KTiOPO_4 and Rb:KTiOPO_4 at 1 µm and 2 µm

Optimum design of high-energy cascaded parametric down-conversion schemes from 1 μm requires accurate knowledge of the laser induced damage threshold (LIDT) of the nonlinear crystal employed. We report surface LIDT measurements in KTiOPO4 (KTP) and Rb:KTP (RKTP) with nanosecond pulses at 1.064 μm and 2.1 μm. LIDT results for nanosecond pulses at 2 μm for KTP and RKTP have not been previously reported to the best of our knowledge.

Direct comparison of kilohertz- and megahertz-repetition-rate femtosecond damage threshold.

We performed femtosecond laser-induced damage threshold (fs LIDT) measurements with substantially different repetition rate Ti:sapphire laser systems: a 1 kHz regenerative amplifier and a 4.3 MHz long-cavity oscillator. All other pulse parameters are kept the same. Comparative measurements of a dielectric high reflector, a chirped mirror, and metallic mirrors show at least a factor of 2.7 lower fs LIDT at megahertz repetition rates. We attribute this to thermally assisted damage mechanisms supported by complex heat transfer simulations.

Comparison of simultaneous on-line optical and acoustic laser damage detection methods in the nanosecond pulse duration domain

We carried out single-shot laser-induced damage threshold measurements on dielectric high reflectors guided by the corresponding ISO standard. Four simultaneous on-line detection techniques were tested and compared using 532 nm, 9 ns and 266 nm, 6 ns laser pulses. Two methods, microscope aided visual inspection and detection of scattered light off the damaged surface, were based on optical signals. The other two techniques exploited the acoustic waves accompanying a damage event in ambient air and in the substrate by a microphone and a piezoelectric sensor, respectively. A unified criterion based on the statistical analysis of the detector signals was applied to assign an objective and unambiguous damage threshold value for all of our diverse detection methods. Microscope aided visual inspection showed the lowest damage thresholds for both wavelengths. However, the sensitivity of the other three techniques proved to be only slightly lower.

单发大口径光束下介质膜损伤阈值测试

单发大口径光束下介质膜损伤阈值测试

Increasing the laser damage threshold of the Nd:YAG crystal by ArF laser irradiation

A Nd:YAG crystal sample was irradiated by 200 pulses of ArF excimer laser at 35mJ/cm^2 laser fluence and 1Hz repetition rate. The optical absorption of the Nd:YAG crystal was decreased in the whole spectral range of the ultraviolet visible near-infrared region after ArF laser irradiation and some oxygen vacancies of the Nd:YAG crystal were removed according to its additional absorption spectrum. A laser-induced damage threshold (LIDT) measurement of the ArF laser treated crystal was performed by linearly polarized 30ns, 1064nm single longitudinal mode, TEM00 laser pulses. The LIDT of the ArF-laser-irradiated crystal was found to be 302±35 J/cm^2, about three times higher than the LIDT of the unirradiated crystal. Thus, the laser-treated Nd:YAG crystal is preferred to apply as the laser amplifier medium, due to the possibility of further laser amplification caused by the higher damage threshold of the amplifier medium.