Laser-induced sound

Keywords— Laser Percussion, CW CO2 Laser, Biological Tissue, Laser-induced Sound, Microphone. 

C. Method for Measuring the Laser-Induced Sound Waveform... 

A microphone was used to measure the laser-induced sound generated by laser irradiation of a sample over a frequency range of 20-70 kHz. The microphone was set at a distance of 10 cm from the sample surface and at an angle of 45° to the surface. Frequency analysis of the generated laser-induced sound was performed using analytical software TDS waveform utility. 

Fig. 2 shows the waveform of the laser-induced sound produced by laser irradiation of 10 wt% gelatin. The laser power was 10 W, the irradiated area was 1 mm in diameter, the laser intensity was 1.27 kW/cm, and the irradiation time was 1 s. The laser-induced sound has an intermittent waveform. Fig. 3 shows expanded plots of the first laser-induced sounds for the six samples (i.e., pork, spongy bone, cortical bone, meniscus, fat, and bone marrow). The laser power was 10 W, the irradiated area was 1 mm in diameter, the laser intensity was 1.27 kW/cm, and the irradiation time was 80 ms. 

Fig. 2 Laser-induced sound waveform by CW CO2 laser. The induced sound has an intermittent waveform. The laser-induced sound generated at a time of 0 ms is termed the first laser-induced sound...

The laser-induced sound waveform was characterized by (a) the pressure amplitude, (b) the attenuation time, (c) the ratio of the first and third peaks, (d) the fall time (third peak) (see Fig. 4). These parameters are defined as follows. The pressure amplitude is defined as the difference between the maximum and minimum pressures of the laser-induced sound. The attenuation time is defined as the time that the laser-induced sound pressure decreases from it maximum value to 1/lOth its maximum value. The ratio of the first to third peaks is defined as the ratio of the first peak height to the third peak height. The fall time is defined as the time for the pressure to change from 0 to its value at the third induced sound peak. 

Fig. 3 First laser-induced sound waveforms of various tissues. The samples exhibit different sound amplitudes and waveforms...

Fig. 4 Analysis of laser-induced sound waveforms (1) pressure amplitude, (2) attenuation time, (3) ratio of the first and third peaks, (4) fall time...

Fig. 7 Laser-induced sound frequency characteristics of various tissues. Frequency analysis was performed from 0 to 120 ps...

Fig. 5 Laser-induced sound properties of various tissues, (a) The maximum pressure amplitude, (b) attenuation time, (c) first and third peaks ratio, (d) fall time (for the third peak)...

An intermittent laser-induced sound waveform was generated by various samples. The laser-induced sound waveform varied depending on the kind of tissue. This... 

If the system under consideration is chemically inert, the laser excitation only induces heat, accompanied by density and pressure waves. The excitation can be in the visible spectral region, but infrared pumping is also possible. In the latter case, the times governing the delivery of heat to the liquid are those of vibrational population relaxation. They are very short, on the order of 1 ps this sort of excitation is thus impulsive. Contrary to a first impression, the physical reality is in fact quite subtle. The acoustic horizon, described in Section VC is at the center of the discussion [18, 19]. As laser-induced perturbations cannot propagate faster than sound, thermal expansion is delayed at short times. The physicochemical consequences of this delay are still entirely unknown. The liquids submitted to investigation are water and methanol. 

Ultrasonic experiments using laser induced phonon spectroscopy have been performed in a nematic liquid single crystal elastomer [48]. The experiments reveal a dispersion step for the speed of sound and a strong anisotropy for the acoustic attenuation constant in the investigated frequency range (100 MHz -1 GHz). These results are consistent with a description of LCEs using macroscopic dynamics [54-56] and reflect a coupling between elastic effects and the nematic order parameter as analyzed in detail previously [48]. 

F. Sundstrom, K. Fredriksson, S. Montan, U. Hafstrom-Bjdrkman, J. Strom Laser-induced fluorescence from sound and carious tooth substance Spectroscopic studies. Swed. Dent. J. 9, 71 (1985)... 

In later chapters where we study laser-induced acoustic (sound, density) waves in liquid crystals, or generally when one deals with acoustic waves, it is necessary to assume that the density p(f, t) is a spatially and temporally varying function. In this chapter, however, we decouple such density wave excitation fi om all the processes under consideration and basically limit our attention to the flow and orientational effects of an incompressible fluid. In that case we have... 

Khoo, I. C., and R. Normandin. 1984. Nanosecond laser-induced transient and permanent gratings and ultrasonic waves in smectic film. J. Appl. Phys. 55 1416 see also Mullen, M. E, B. Uthi, and M. J. Stephen. 1972. Sound velocity in nematic liquid crystal. Phys. Rev. Lett. 28 799 Lord, Jr., A. E. 1972. Anisotropic ultrasonic properties of smectic liquid crystal, ibid. 29 1366. 

Kozlov DN, Kiefer J, Seeger T, Froba AP, Leipertz A (2014) Simultaneous measurement of speed of sound, thermal diffusivity, and bulk viscosity of l-ethyl-3-methylimidazolium-based ionic liquids using laser-induced gratings. J Phys Chem B 118 14493-14501... 

See, for example. H. Eichler and H. Stahl. ""Time and frequency behavior of sound waves thermally induced by modulated laser pulses, J. Appl. Phys., vol. 44. pp. 3429-3435. 1973. 

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