Characteristic features of the laser ablation of foam graphite

Analysis of the structure of foam graphite by optoacoustic spectroscopy and scanning electron microscopy

“…The angle was determined from the expression tg a = dX/deÂde/dR, where X and e are the average depth of the crater per pulse and the laser flux taken from the previous paper. 7 In the case of normal distribution of the laser flux with s = 80 AE 5 mm and e 0 = 2.4 AE 0.1 J cm 72 , the angle a near the bottom of the crater is 108. Here the average repetition period of the layers is 0.66 AE 0.07 mm, and 0.46 AE 0.05 mm of it is the total air gap within the layers.…”

“…those obtained by heating oxidised graphite, 6 have been noted in a number of our studies. Considerable interest was attracted by the low heat of vaporisation of this thermoexpanded (foam) graphite, 7,8 indicating vaporisation of large graphite fragments which can be used for the synthesis of carbon nanoclusters. 9 The qualitative difference between the mechanisms of vaporisation of foam graphite and conventional polycrystalline graphite is obviously due to the structural properties of these materials.…”

“…9 The qualitative difference between the mechanisms of vaporisation of foam graphite and conventional polycrystalline graphite is obviously due to the structural properties of these materials. 7,8 The ideal crystalline graphite with density r cg = 2.25 g cm 73 is an infinite crystallite consisting of twodimensional graphite layers 3.35 A apart, which leads to anisotropic properties. 10 Polycrystalline graphite (PCG) with density r pcg = 1.7 g cm 73 differs in that it has a close packed array of chaotically oriented separate crystallites of 50±500 A and has spatially isotropic properties.…”

Photoacoustic detection of the spinodal decay of carbon

“…The resolution of these components, which is impossible in real time due to diffraction and dissipation of the high-frequency component of the Fourier spectrum of the acoustic signal in the lamellar structure of graphite, was achieved by suppressing the thermoacoustic wave of rarefaction (formed upon reflection of the thermoacoustic wave of compression from the free surface of the target) by the recoil pressure wave of compression. The photoacoustic study was performed on a set-up 4 that enabled measurement of the mean crater depth during a pulse (X) as well as the thermoacoustic and recoil pressures. A portion of irradiation of the second harmonics of a pulse Nd:YAG laser [pulse energy 5 mJ in the TEM 00 mode (stability 6%), pulse length (FWHM) 25 ns, pulse repetition rate 12.5 Hz] was fed to a photodiode and a pyroelectric in order to synchronise the system of recording and control of laser irradiation energy at each pulse.…”

Photoacoustic detection of the parameters of laser vaporisation of amorphous carbon nitride

“…A number of parameters were determined by the photoacoustic method, namely, the absorption (extinction) coefficient at the wavelength of laser irradiation and the velocities of ultrasonic waves, which determine the character of the amorphous carbon nitride vaporisation under laser irradiation. In the experiments we used a photoacoustic device, 6 which enabled measurement of the sound velocity and the mean crater depth during a laser pulse. A pulsed Nd:YAG laser provided an output energy of 5 mJ per pulse of the second harmonic irradiation (532 nm) in the TEM 00 mode at 6% stability, pulse length (FWHM) t Las = 25 ns and pulse repetition rate f Las = 12.5 Hz.…”