Laser Calorimetry Research Articles

Accurate Determination of the Low-Light-Level Absorption of DUV-Fused Silica at 193 nm with Laser Calorimetry

The low-light-level absorption coefficient of OH-contained and H2-impregnated synthetic fused silica material in 193 nm optical lithography application is determined via a laser calorimetry measurement. The fluence and repetition rate dependences of the absorptances of the deep ultraviolet (DUV)-fused silica samples with different thickness are measured. The measured dependences are fitted to a theoretical model, taking into consideration the generation and annealing of laser irradiation induced defects. The surface absorption, the low-light-level linear absorption coefficient, as well as the nonlinear absorption coefficient of the fused silica material are accurately determined via the fitting. The low-light-level linear absorption coefficients determined via the fluence dependence and the repetition rate dependence are in good agreement, demonstrating the reliability of the measured low-light-level absorption coefficient, which is the key parameter to the determination of the internal transmission of the DUV-fused silica material used in the 193 nm optical lithography.

RF oscillator circuit for absorption coefficient measurement of piezoelectric materials.

We have introduced an approach for low optical absorption coefficient measurement of piezoelectric materials based on the piezoelectric resonance laser calorimetry (PRLC) method. An RF oscillator circuit provides a convenient way to track the piezoelectric resonance frequency during laser irradiation. In this work, the optical absorption coefficient of lithium triborate crystal under high-power IR laser irradiation was measured using the oscillator circuit and the conventional PRLC technique.

Autogenously self-healable cementitious composite incorporating autolytic mineral microspheres: Hydration regulation and structural alteration

This work proposes a novel insight into the autolytic mineral self-healing strategies for cementitious materials. The autolytic mineral microsphere (AMM) was prepared via the fluidization technique with cement clinker/calcium oxide as the healing substances and amino trimethylene phosphonic acid as the autolytic coating film. The basic characteristics of AMM and its hydration influence on the cementitious composite were analyzed by the laser particle analyzer, calorimetry, X-ray diffractometry and scanning electron microscopy. The autogenous self-healing capacity of the cementitious composite incorporating AMM was assessed by the crack closure, flexural property restoration and electrochemical impedance spectroscopy. Through the autolytic procedure, AMM regulated the hydration evolution and enhanced the self-healing performance of cementitious composite. The AMM containing cement clinker steadily healed the crack, leading to a well regeneration of fractured structure and restoration of flexural property. The partial substitution of cement clinker by calcium oxide in AMM further increased the crack filling, but induced a volume instability of the cement matrix as well, resulting in the strength decrease under a long-term secondary hydration. The structural alteration of cementitious composite was predominately impacted by the self-healing effect in the first 28 d re-curing, whilst the volume instability effect played a dominant role subsequently.

Measurements of small optical absorption and scattering coefficients of high-power polarised laser radiation in lithium triborate crystals

We present the results of measurements of low optical absorption and scattering coefficients in lithium triborate crystals using the method of piezoelectric resonance laser calorimetry under the action of polarised single-mode laser radiation at wavelengths of 1070 and 532 nm in the power ranges of 50 – 300 and 5 – 50 W, respectively. It is shown that when radiation propagates along the crystal axis a, these coefficients remain constant in the specified power ranges and do not depend on the direction of laser radiation polarisation. The measured optical scattering coefficients are compared with the results obtained by the method of integrating spheres.

Ultra-Rapid Laser Calorimetry for the Assessment of Crystallization in Low-Concentration Cryoprotectants.

Cryoprotective agents (CPAs) are routinely used to vitrify, attain an amorphous glass state void of crystallization, and thereby cryopreserve biomaterials. Two vital characteristics of a CPA-loaded system are the critical cooling and warming rates (CCR and CWR), the temperature rates needed to achieve and return from a vitrified state, respectively. Due to the toxicity associated with CPAs, it is often desirable to use the lowest concentrations possible, driving up CWR and making it increasingly difficult to measure. This paper describes a novel method for assessing CWR between the 0.4 × 105 and 107 °C/min in microliter CPA-loaded droplet systems with a new ultrarapid laser calorimetric approach. Cooling was achieved by direct quenching in liquid nitrogen, while warming was achieved by the irradiation of plasmonic gold nanoparticle-loaded vitrified droplets by a high-power 1064 nm millisecond pulsed laser. We assume “apparent” vitrification is achieved provided ice is not visually apparent (i.e., opacity) upon imaging with a camera (CCR) during cooling or highspeed camera (CWR) during warming. Using this approach, we were able to investigate CWRs in single CPA systems such as propylene glycol (PG), glycerol, and Trehalose in water, as well as mixtures of glycerol-trehalose-water and propylene glycol-trehalose-water CPA at low concentrations (20–40 wt %). Further, a phenomenological model for determining the CCRs and CWRs of CPAs was developed which allowed for predictions of CCR or CWR of single component CPA and mixtures (within and outside of the regime their constituents were measured in), providing an avenue for optimizing CCR and CWR and perhaps future CPA cocktail discovery.

The potential of chemical bonding to design crystallization and vitrification kinetics

Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications. Nevertheless, design rules for crystallization and vitrification kinetics still lack predictive power. Here, we identify stoichiometry trends for these processes in phase change materials, i.e. along the GeTe-GeSe, GeTe-SnTe, and GeTe-Sb2Te3 pseudo-binary lines employing a pump-probe laser setup and calorimetry. We discover a clear stoichiometry dependence of crystallization speed along a line connecting regions characterized by two fundamental bonding types, metallic and covalent bonding. Increasing covalency slows down crystallization by six orders of magnitude and promotes vitrification. The stoichiometry dependence is correlated with material properties, such as the optical properties of the crystalline phase and a bond indicator, the number of electrons shared between adjacent atoms. A quantum-chemical map explains these trends and provides a blueprint to design crystallization kinetics.

Aggregation affects optical properties and photothermal heating of gold nanospheres

Laser heating of gold nanospheres (GNS) is increasingly prevalent in biomedical applications due to tunable optical properties that determine heating efficiency. Although many geometric parameters (i.e. size, morphology) can affect optical properties of individual GNS and their heating, no specific studies of how GNS aggregation affects heating have been carried out. We posit here that aggregation, which can occur within some biological systems, will significantly impact the optical and therefore heating properties of GNS. To address this, we employed discrete dipole approximation (DDA) simulations, Ultraviolet–Visible spectroscopy (UV–Vis) and laser calorimetry on GNS primary particles with diameters (5, 16, 30 nm) and their aggregates that contain 2 to 30 GNS particles. DDA shows that aggregation can reduce the extinction cross-section on a per particle basis by 17–28%. Experimental measurement by UV–Vis and laser calorimetry on aggregates also show up to a 25% reduction in extinction coefficient and significantly lower heating (~ 10%) compared to dispersed GNS. In addition, comparison of select aggregates shows even larger extinction cross section drops in sparse vs. dense aggregates. This work shows that GNS aggregation can change optical properties and reduce heating and provides a new framework for exploring this effect during laser heating of nanomaterial solutions.

Measurement of the absorption coefficient of a periodically poled LiNbO3 crystal at a radiation wavelength of 3 μm

Problem formulating. In the case of nonlinear-optical conversion of high-power laser radiation in nonlinear-optical crystals the optical absorption leads to a nonuniform heating of the crystals, which results in the violation of phase matching conditions, the formation of defects, and optical damage. Goal. Measurements of optical absorption coefficient of the periodically poled lithium niobate (PPLN) crystal at 3 μm radiation wavelength using the piezoelectric resonance laser calorimetry (PRLC). Result. The optical absorption coefficient of PPLN crystal at 3.045 μm radiation wavelength was measured using the piezoelectric resonance laser calorimetry. The value (1.15±0.15) 10⋅ -2cm-1 of absorption coefficient within the measurement error limits was independent of the initial temperature of PPLN and the incident radiation power in the ranges 293–343 K and 0.2–10 W respectively. Practical meaning. The interaction of mid-IR laser radiation with PPLN crystal was studied using the piezoelectric resonance laser calorimetry.

Assessment of critical warming and cooling rates of low concentration cryoprotectants via ultra-rapid laser calorimetry and liquid nitrogen quenching

Assessment of critical warming and cooling rates of low concentration cryoprotectants via ultra-rapid laser calorimetry and liquid nitrogen quenching

ArF laser-induced damage of calcium fluoride windows with protected anti-reflection coatings

High-power ArF lasers for high-volume production of mobile consumer microelectronics demand low loss and laser durable calcium fluoride (CaF2) laser-windows. Increased laser durability is realized by F-SiO2 protective coatings on CaF2 windows with subsurface-damage-free (SSD-free) surface finishing. Surface reflection loss is reduced by fluoride-based anti-reflection (AR) coatings. In this contribution, we integrated the protective coating with the fluoride-based AR coatings on SSD-free CaF2 windows and assessed the laser damage resistance of the window using an ArF laser with a pulse length of 20 ns and a rep rate of 20 Hz. Damage initiation sites were detected on the entrance surface at a fluence of 3.5 J / cm2. A 100% damage probability was determined at a fluence of 5 J / cm2. An absorption-driven thermal damage mechanism was indicated by the damage morphology. Similar laser damage resistance was realized on the protected AR-coated windows with more than 9% transmission gain when compared to that of the F-SiO2 protected CaF2 laser-windows. The results suggest that two-photon absorption is a dominant factor when nonlinear absorption occurs in the laser-irradiated CaF2 windows. The thermally induced damage could be further simulated using the experimentally determined two-photon absorption coefficient based on the ArF laser calorimetry technique.

Effect of droplet deformation on determination of thermal conductivity in modulated laser calorimetry

The modulated laser calorimetry method using electromagnetic levitation is a superior way for measuring the thermal conductivity of molten materials. In this method, the top of droplet is periodically heated by modulated laser and the temperature response of bottom droplet is monitored by promoter simultaneously. By fitting the numerically obtained phase lag between laser and temperature response to that measured in experiments, the thermal conductivity is determined. However, in numerical analysis, the shape of droplet is usually fixed to be sphere while visible deformation of molten droplet is observed during experiments. The omitting of droplet deformation would surely affect the accuracy of measured thermal conductivity. In this work, a series of axisymmetric simulations are performed to investigate the influence of deformation of an electromagnetically levitated droplet on the determination of thermal conductivity. The results show that although the temperature distribution is inhomogeneous due to the physical nature of skin effect, the phase lag between modulated laser and temperature response is completely unaffected. Besides, the phase lag decreases with more intense convection and increases with droplet deformation. The effective thermal conductivity measured is about 16.8% smaller than inherent value under deformation rate of 12.2%. Moreover, a wider gap between the effective thermal conductivity and inherent value can be predicted under severer deformation. The relationship between thermal conductivity and deformation rate is linear and it applies to droplets with different radii and materials. Therefore, effective thermal conductivity can be corrected to determine the inherent value according to deformation rate. With this work, it is expected that the measurement accuracy of thermal conductivity can be further enhanced by taking the deformation of droplet into account.

Acoustic resonance laser calorimetry for measurements of low optical absorption.

A novel method of acoustic resonance laser calorimetry (ARLC) for the determination of low optical absorption coefficients of crystals and glasses is introduced. It is based on measurements of the kinetics of the equivalent temperature of the sample irradiated by the pulse laser radiation. The equivalent temperature of the sample is directly obtained by measuring the frequency changes of its temperature-calibrated acoustic resonances excited by the laser radiation with a corresponding pulse repetition rate. In contrast to the conventional resonant photoacoustic spectroscopy, where the resonance is used for the enhancement of the registered signal, in ARLC, the laser-excited acoustic resonance of the sample acts as a high-sensitivity temperature probe for measurements of its heating kinetics. The ARLC approach was verified by measuring the optical absorption coefficient of the potassium dihydrogen phosphate crystal (α=4.2⋅10-2cm-1) at 1064 nm wavelength.

Laser calorimetry for assessment of melting behaviour in multi-walled carbon nanotube decorated aluminium by laser powder bed fusion

Material development for powder bed fusion is critical to enhance the utility of the process. Establishing process parameters for new materials limits the rate at which process performance can be appraised. Adapted laser calorimetry is a useful technique for rapid material screening. Here, multi-body feedstocks which have the potential to improve laser coupling and mechanical properties of structures (Al + multi-walled carbon nanotubes) are investigated to demonstrate the flexibility of laser calorimetry for understanding consolidation and heat transfer phenomena in powder bed fusion. It is shown that the modifications to powder surface condition/chemistry improve consolidation behaviour in this case.

Determination of specific losses in highly transparent Nd : YAG ceramics by laser calorimetry

Specific absorption losses in five samples of (1% – 4%) Nd : YAG optical ceramics are measured by laser calorimetry. The measurement results show that the specific losses increase from 7 × 10−3 to 13 × 10−3 cm−1 as the neodymium concentration increases above 2 at%. The principal possibility of separate determination of scattering and absorption losses using additional measurements of total losses in ceramic material is shown.

Anisotropy of nonlinear optical absorption of LBO crystals at 355 nm.

The dependence of the nonlinear optical absorption coefficients on the intensity and polarization of pulsed laser radiation at 355nm was investigated for lithium triborate (LBO) crystals using the piezoelectric resonance laser calorimetry.

Laser Calorimetry Spectroscopy for ppm-level Dissolved Gas Detection and Analysis

In this paper we report a newly developed technique – laser calorimetry spectroscopy (LCS), which is a combination of laser absorption spectroscopy and calorimetry - for the detection of gases dissolved in liquids. The technique involves determination of concentration of a dissolved gas by irradiating the liquid with light of a wavelength where the gas absorbs, and measuring the temperature change caused by the absorbance. Conventionally, detection of dissolved gases with sufficient sensitivity and specificity was done by first extracting the gases from the liquid and then analyzing the gases using techniques such as gas chromatography. Using LCS, we have been able to detect ppm levels of dissolved gases without extracting them from the liquid. In this paper, we show the detection of dissolved acetylene in transformer oil in the mid infrared (MIR) wavelength (3021 nm) region.

Role of HfO2/SiO2thin-film interfaces in near-ultraviolet absorption and pulsed laser damage

The role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO2 and SiO2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO2 single-layer film and for a film containing seven narrow HfO2 layers separated by SiO2 layers. The seven-layer film was designed to have a total optical thickness of HfO2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similar to a single-layer HfO2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO2 and SiO2 materials.

Surface losses in the visible governed by Rayleigh scattering in synthetic diamonds

Measurements of surface loss throughout the visible and in the near-infrared on a single crystal diamond using laser calorimetry reveal that it is governed by Rayleigh scattering. This was confirmed by Atomic Force Microscopy that revealed surface roughness much smaller than the wavelengths used. There is no detectable contribution from surface absorption on this material as finished and cleaned. Measuring the dispersion of surface loss offers a powerful tool in determining its cause.

Intrinsic and extrinsic absorption of chemical vapor deposition single-crystal diamond from the middle ultraviolet to the far infrared

Optical absorption is reported in high-quality single-crystal Type IIa diamonds grown by microwave-assisted chemical vapor deposition. Laser calorimetry and spectrophotometry were used at wavelengths from the ultraviolet to the infrared. There is minimal evidence of extrinsic absorption on or near the short wavelength side of the middle-ultraviolet (MUV) region (200–300 nm) or in the infrared absorption bands. At the long wavelength side of the MUV and extending into the visible, extrinsic absorption dominates, which is related to the amount of nitrogen and nitrogen-related lattice defects in diamond. In the samples studied nitrogen concentrations were between 10 and 40 ppb. At 10.6 μm, the measured absorption coefficient of a representative sample is comparable with, or less than, those of the highest quality samples previously reported. Evidence is presented showing that our measurements serve as upper bounds on the absorption coefficients and call into question previous calorimetric reports of intrinsic absorption in the visible, near infrared, and at 10.6 μm.

Thermal lensing in Er, Yb : YVO4 crystal

A thermal lens is characterized in 0.7 at.%Er, 3 at.%Yb : YVO4 yttrium vanadate crystal cut along the [1 0 0] crystallographic axis, for π and σ laser polarizations, by a probe beam method. For a pump spot radius of 100 μm and π-polarization, sensitivity factors of the thermal lens equal 5.7 and 7.9 m−1 W−1 (parallel and perpendicular to the [0 0 1]-axis, respectively); the astigmatism degree is 28%. The fractional heat load is determined by ISO-standard laser calorimetry, ηh = 0.63 ± 0.05. The anisotropy of the photo-elastic effect plays a dominant role in the formation of the astigmatic thermal lens.