Recent developments in photoacoustic imaging and sensing for nondestructive testing and evaluation

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Table 2 Technical specifications of PA technologies used for NDT/E (representative examples)

PA technology for NDT/E	Laser wavelength (nm)^a	Lateral resolution; axial resolution (µm)	US frequency of ultrasound transducer (MHz)	Ref.
1. Modulated CW laser for PA wave excitation	830	100; NA	NA	[19]
2. Pulsed laser for PA wave excitation
2.1 PA Aline and simple imaging	1064	NA; NA	1−100	[37]
2.2 PACT	532	2000; NA	40	[38]
2.3 PAM^b	1064	525; NA	20	[40]
2.3 PAM^b	532	3.3; 26	35	[11]
3. PA-generated US waves as sources	532	1.7^c; NA	20 and 93	[51]
4. All-optical PA wave excitation and detection	532	NA; NA	NA	[35]

^aFor PA excitation; ^bFor AR-PAM [40] and OR-PAM [11]; ^cFor the transmitter. NA: Not applicable