A quantitative analysis of linear temperature-dependent coupled thermoelectronic diffusion waves in the generation of the laser-induced IR photothermal radiometric signal from a photoexcited, plasma-wave-dominated, semi-infinite semiconductor Si wafer is presented. The strong coupling between the (usually assumed decoupled) carrier and thermal wave transport equations is accounted for explicitly and the range of violation of the Vasil’ev-Sandomirskii condition is studied. Thermoelectronic coupling is found to degrade the sensitivity of the plasma-originating IR radiometric signal in high-quality process Si substrates at elevated background temperatures and high modulation frequencies, with the exception of highly degenerate plasmas. © 1997 Society of Photo-Optical Instrumentation Engineers.

Combining the ideas behind linear frequency modulated continuous wave radars and frequency domain photothermal radiometry (PTR), a novel PTR method is introduced. Analytical solutions to the heat diffusion problem for both opaque and transparent solids are provided. Simulations and experimental results suggest a significant improvement in the dynamic range when using the thermal-wave radar (TWR) instead of conventional PTR. A practical TWR image resolution augmentation method is proposed.

In this study, we report for the first time the use of silica-coated superparamagnetic iron oxide nanoparticles (SPION) as contrast agents in biomedical photoacoustic imaging. Using frequency-domain photoacoustic correlation (the photoacoustic radar), we investigated the effects of nanoparticle size, concentration and biological media (e.g. serum, sheep blood) on the photoacoustic response in turbid media. Maximum detection depth and the minimum measurable SPION concentration were determined experimentally. The nanoparticle-induced optical contrast ex vivo in dense muscular tissues (avian pectus and murine quadricept) was evaluated and the strong potential of silica-coated SPION as a possible photoacoustic contrast agents was demonstrated.

One major problem of frequency-domain photothermal radiometry, or alternatively in two-dimensional lock-in thermography, is the compromise one has to make between dynamic range (probing depth) and depth resolution. The thermal-wave radar incorporates chirped excitation through matched filtering to maintain good resolution and depth range inside a sample. This letter experimentally demonstrates the advantages of chirped modulation and introduces a thermophotonic modality of thermal-wave radar based on an emissivity-normalized, higher-dynamic-range contrast parameter known as cross-correlation phase. Finally, comparisons made on a biological (dental) sample show potential applications of the method.

Condition monitoring, nondestructive testing and fault diagnosis are currently considered crucial processes for on-condition maintenance (OCM) to increase the reliability and availability of wind turbines and reduce the wind energy generation cost. Carbon fiber reinforced plastics (CFRP) have been increasingly used to fabricate wind turbine blades. Delamination type damage is inevitable during manufacture or in-service of a CFRP blade. This inner (subsurface) flaw, usually difficult to be detected by artificial visual inspection or machine vision based on CCD or CMOS, severely degrades the load bearing capacity of a blade. Induction infrared thermography (IIT) is an emerging infrared machine vision inspection technology, which has the capability of insight to CFRP based on electromagnetic induction and heat conduction. This paper introduces photothermal thermal-wave radar (TWR) non-destructive imaging (NDI) to IIT, based on cross correlation (CC) pulse compression and matched-filtering and applies TWR principles to CFRP imaging inspection and diagnosis. The experimental studies carried out under the transmission mode have shown that TWR B-scan and phasegram can be used to inspect and diagnose subsurface delaminations in CFRP with improved SNR and shape identification. As a new machine vision inspection method, TWRI will play an important role in the OCM of wind turbine blade.

Frequency-domain photothermoacoustic (FD-PTA) imaging of biological tissues is presented and compared with the conventional time-domain methodology. We demonstrate that tissue imaging can be performed with high axial resolution without the necessity to employ short-pulse and high peak-power laser systems to generate acoustic transients. The presented analysis shows that depth information in the FD-PTA method can be recovered by using linear frequency-modulated (chirped) optical excitation and frequency-domain signal processing algorithms. The signal-to-noise ratio can be increased significantly using correlation processing, which can compensate for the small amplitude of acoustic waves typical to the periodic excitation mode. Additionally, narrow-band signal demodulation enables depth-specific and confocal tissue imaging using the optically induced photothermoacoustic effect. Application of the FD-PTA is demonstrated in experiments with turbid phantoms and ex vivo tissue specimens.