Transfer function of the laser beam deflection probe for detection of cylindrical acoustic waves in a transverse arrangement

We examine detection of cylindrical acoustic waves by a laser beam probing the wave orthogonally to the symmetry axis. Considering the probe as a linear system transforming acoustic waveform into transient angular deflection of the probe beam we derive its transfer function

A study of energy conversion during Nd :YAG laser ablation of metal surfaces in air by means of a laser beam deflection probe

We measure shock wavefront transition times of optoacoustic (OA) transients generated in air during laser ablation and employ the solution of the point explosion model to determine blast energy of the OA transients. We examine the dependence of OA energy conversion efficiency on laser energy and pulse duration

THE DECREASE OF OPTOACOUSTIC SIGNALS INDUCED BY THE ABSORPTION OF MEDIUM INTENSITY LASER PULSES ON SOLIDS

Les mesures simultanées des signaux optoacoustiques dans le solide absorbant et dans le gaz qui l'entoure sont accomplies pour étudier les modifications de la surface causées par l'absorption des quelques impulsions initiales du laser de fluence 0,4 J/cm2 et de durée 20 ns.Simultaneous measurements of optoacoustic signals in the absorbing solid and in the surrounding gas have been performed in order to study surface modifications on various solids, caused by the absorption of the firts few laser pulses of fluence 0.4 J/cm2 and duration 20 ns

Influence of plasma shielding in optoacoustic measurements

Simultaneous measurements of laser excited ultrasonic waves in a solid sample and in the surrounding air were used for characterizing the plasma shielding effect and for the evaluation of its influence in optoacoustic measurements. Typical modifications of ultrasonic waves are discussed and the acoustic energy distribution between the solid and the atmosphere is assessed by a comparative analysis of optoacoustic responses received from both probes

Pulsed photoacoustic studies of thermoset curing reaction

A pulsed photoacoustic technique was used for generation of ultrasonic pulses along with optical detection inside a transparent polymer resin undergoing a curing reaction. The changes in acoustic parameters during the solidification process was measured and were found to agree with the accepted general model for the kinetics of the curing reaction for polyester and epoxy resins. The advantages of the acoustic characterization compared to the more common calorimetric techniques are considered

Comparison of four methods for estimating relative solar radiation in managed and old-growth silver fir-beech forest

Methods based on the principle of hemispherical canopy projection, including hemispherical photography (digital andfilm), sensors like LAI 2000 (zenith cutoff anle 74,1°) andstable horizontoscope, represent less accurate, yet significantly less expensive andtime-consuming techniques for radiation measurements comparedto long-term measurement with a network of photosynthetically active radiation (PAR) sensors. With measurements taken at a single point in time they can provide reliable estimates of relative diffuse andd irect solar radiation andcan also be usedto estimate the light climate in different times of the year. The four above mentioned methods for solar radiation estimation were applied at the same points in gaps and under adjacent canopies in unevenaged, mixed Dinaric fir-beech and pure beech montane forests. Locations covereda range of radiation andstandstructure conditions. Data analyses showedgoodreliability of all four methods over the whole range (2–80%) of radiation conditions. The most comparable results come from LAI 2000 andfilm hemispherical photography (all R > 0.90). Digital hemispherical photography is an accurate andreliable (R = 0.89) replacement for film hemispherical photography, but the higher values estimatedfor direct radiation should be taken into account. Compared to the other three methods, the stable horizontoscope gives less accurate results, especially under canopies with poorly defined gaps. Our study showed that all four methods tested are suitable for estimating the solar radiation climate in gaps and stands with heterogeneous vertical structures, andhave potential value as a tool in decision making when practicing silviculture