Frequency Characteristics of Surface Wave Generated by Single-Line Pulsed Laser Beam with Two Kinds of Spatial Energy Profile Models: Gaussian and Square-Like

Abstract

Using a single-line pulsed laser beam is well known as a useful noncontact method to generate a directional surface acoustic wave. In this method, different laser beam energy profiles produce different waveforms and frequency characteristics. In this paper, we considered two typical kinds of laser beam energy profiles, Gaussian and square-like, to find out a difference in the frequency characteristics. To achieve this, mathematical models were proposed first for Gaussian laser beam profile and square-like respectively, both of which depended on the laser beam width. To verify the theoretical models, experimental setups with a cylindrical lens and a line-slit mask were respectively designed to produce a line laser beam with Gaussian spatial energy profile and square-like. The frequency responses of the theoretical models showed good agreement with experimental results in terms of the existence of harmonic frequency components and the shift of the first peak frequencies to low.

Nondestructive Evaluation of Thermal Aging in Al6061 Alloy by Measuring Acoustic Nonlinearity of Laser-Generated Surface Acoustic Waves

“…The burst count and frequency characteristics can be modulated by using a line-arrayed slit mask for the expanded laser shot [34,35]. Theoretical and experimental studies about the modulation are well-described in our previous works [36,37]. When the distribution of laser intensity is a single-line Gaussian, the generated SAW has a single fundamental frequency component of a broad bandwidth.…”

“…, where is the width of the opening and d is the interval between the slit lines [13,36]. With 0.5 γ = , the even-order harmonic frequency components are theoretically zero [37].…”

“…The multiple-line laser of square-like intensity distribution is appropriate to narrow the bandwidth, as shown in Figure 4. The harmonic frequency components can be modulated by the duty ratio (γ = w/d), where w is the width of the opening and d is the interval between the slit lines [13,36]. With γ = 0.5, the even-order harmonic frequency components are theoretically zero [37].…”

Influence of laser beam profiles on the frequency bandwidth of laser-generated surface acoustic waves

“…For this reason, SAWs generated by different laser beam profiles can lead to different frequency characteristics [10,11]. The SAW generated by a single-point laser beam propagates into all directions as well as the wave energy disperses.…”

Initial Second Harmonic Generation in Narrowband Surface Waves by Multi-Line Laser Beams for Two Kinds of Spatial Energy Profile Models: Gaussian and Square-Like

“…Laser-ultrasonic technique provides a flexible and simple method for non-contact and remote generation of ultrasonic surface waves [6][7][8][9][10][11][12][13]. In our previous paper, we have studied the frequency characteristics of surface wave by single-line pulsed laser beam in one-dimensional for two kinds of spatial energy profile models; Gaussian and square-like [13], where it was shown that the frequency spectrum was single broadband at Gaussian laser beam but main lobe with multiple side lobes at square-like laser beam.…”