Laser opto-acoustic study of phase transitions in metals confined by transparent dielectric

Abstract

First order phase transitions in metal induced by nanosecond laser pulse are studied here. The metal surface is irradiated through a layer of transparent dielectric-an optical glass. Such confinement con siderably increases the efficiency of pressure generation at the metal surface. This technique allows to obtain near critical states of metals-with temperatures ~10 4 K and pressures ~10 4 atm with table top equipment. At the same time the glass prevents the ablation plume formation-so the surface temperature can be mea sured using thermal radiation data. An experimental setup for simultaneous measurements of pressure, tem perature and reflectivity was assembled based on the elaborated method of experimental research. The pro cesses of melting of lead and boiling of mercury were studied. The onset of the phase transition process led to a considerable tightening of the pressure pulse. A substantial drop of surface reflectivity due to increase of temperature and decrease of density was observed.

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites

“…The fundamental sensitivity limit is determined by the Johnson-Nyquist noise associated with acoustic detection over a finite spatial aperture and signal bandwidth no matter the modality. 2,3,12,18,19 As will be demonstrated below, the Sagnac-based, non-contact detector developed for our LU system approaches the JohnsonNyquist noise limit and is as sensitive as the best acoustic detectors operating over the same detection area and signal bandwidth.…”

“…10 When the laser pulse duration is varied from $100 ps to $100 ns, generated pressure amplitudes can achieve tens of or even one hundred of MPa, with relatively low (tens of mJ) laser pulse energies. 11,12 A unique feature of laser generated ultrasound (US), or optoacoustic (OA) signals, is their unipolar or bipolar 10 impulse response, which cannot be efficiently duplicated with piezoelectric excitation. Ultimately, the temporal profile of optically generated acoustic signals mimics the laser pulse envelope, i.e., it can be perfectly Gaussian.…”

Nonlinear reflection of a nanosecond laser pulse from thin aluminum film in the temperature range 2–14 kK

“…The thermodynamic cycles of heating and the cooling of materials during which the near-critical and supercritical temperatures are achieved have been studied with respect to the alkali metals [15][16][17], mercury [13,18,19] and lead [13,[20][21][22]. The change of the state of a material is practically unexplored when its temperature rises higher than 3000 K and the pressure within the subsurface region exceeds 200 MPa.…”

Experimental study of the critical point region of aluminum under the action of the powerful nanosecond laser pulse

“…The common disadvantage of these dynamic methods is the narrow band of the produced temperatures and pressures and the limited technical possibilities of their measurement. Currently the parameters for the critical point are reliably measured only for some alkali metals [12][13][14], for mercury [15][16][17] and for lead [2,15,18,19]. The data about the behavior of most of the metals in the vicinity of the critical point, namely the trends of the coexistence curve (binodal) and of the curve of the absolute thermodynamic instability (spinodal) are absent.…”