This special issue presents a collection of selected papers from the field of photoacoustics, presented at the ICPPP21 - The 21st International Conference on Photoacoustic and Photothermal Phenomena, which took place in Bled, Slovenia, from 19 to 24 June 2022.
The conference was attended by 134 scientists from 24 countries. 10 plenary lectures were delivered by leading researchers in the fields of biomedical imaging, thermophysical properties of materials, materials' research and characterization, ultrafast phenomena and spectroscopy, nanostructures and nanoscale phenomena, analytical chemistry and photochemistry, and new methodologies, instrumentation and applications of photoacoustic and photothermal techniques. In addition, 26 keynote lectures and 77 short oral presentations were given, while 69 posters were on display during the conference.
Over the past decade the emphasis of the contributions to the ICPPP conferences has very much shifted towards the development and applications of photoacoustics in medical diagnostics. However, applications of photoacoustic spectroscopy for gas sensing still remains one of the most popular research topics in this field. This is also reflected in the fact that the majority of papers in this collection is related to gas sensing, where principles of quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES) are finding application in multi-gas photoacoustic sensors. Their development is supported by utilization of novel laser technologies like for example the Vernier effect-based quantum cascade lasers (Zifarelli et al.) or approaches such as univariate calibrations (Sampaolo et al.), Beat Frequency-QEPAS (Spagnolo et al.), and newly designed open photoacoustic cells, which are better suited for measurements in rapidly flowing gases (Bozoki et al.).
In the area of medical diagnostics one can observe continuous efforts to improve the quantitative imaging capabilities in photoacoustic tomography. A possible approach is photoacoustic spectrum analysis, which enables detection of size and optical properties of spherical objects as they are frequently encountered in diagnostic applications (Dantuma et al.). Research is also focusing on imaging multiple tissue properties and biomarkers with high resolution, penetration and contrast. This was achieved by devising a hybrid transmission-reflection optoacoustic ultrasound imaging platform (TROPUS), which was tested in vivo on small animals. The TROPUS platform shows suitability for detection and assessment of non-alcoholic fatty liver disease in preclinical model studies (Razansky et al.). On the other end, progress in development of photoacoustic devices for medical applications includes a high-sensitivity high-resolution intravascular photoacoustic catheter, which relies on mode cleaning in a graded index fiber (Cheng et al.), as well as a multi-position calibrated photoacoustic thermometer for photothermal therapy monitoring in-vivo, which utilizes the temperature dependence of the photoacoustic conversion efficiency (Xiao et al.).
Other contributions in this special issue present latest advances in experimental detection of pressure-induced acoustic waves, which are relevant for characterisation of materials, further advancement of optical manipulation technology of deformable matter, and for empirical validation of electrodynamic formalisms, such as the basic definition of electromagnetic momentum density in matter (Astrath et al.). Furthermore, ultrafast measurements of shock wave rise times in low viscosity liquids provide the necessary data for the study and understanding of the shock wave formation and propagation in fluids (Horvat et al.). Last but not the least, further advancement in photoacoustics very much depends on the development of novel excitation sources, like for example ultrasonic photoacoustic emitters composed of graphene nanocomposite films, which provide high amplitude focused ultrasound and bear the scope for compact, highly-efficient, and inexpensive photoacoustic components for biomedical application and sonochemistry (Vella et al.). Another possible excitation source is a FERMI seeded free electron laser, which was for the first time presented to ICPPP conference participants as the source for transient grating generation in the extreme UV range, which opens the door to nanoscale photoacoustics and the possibilities to generate and detect the dynamics of bulk and surface phonons on previously inaccessible wavelength range (Foglia et al.).
Biographies
Mladen Franko is a Professor of Chemistry at the University of Nova Gorica, where among other functions he served as Head of the Laboratory for environmental and life sciences (2013–2021) and as Vice-rector for education (2010–2022). His research interests and expertise include: development and application of new analytical methods based on laser photothermal spectroscopy for detection of heavy metals and their species and organic compounds following chromatographic separation and FIA, including microfluidic systems; development of new biosensors and laser detection techniques for determination of toxic and essential compounds in environmental and biological samples; and optical, thermal and structural characterization of composite materials by photothermal techniques. For his scientific achievements in analytical chemistry, he was awarded the “Zois Prize” - State Award for Science of the Republic of Slovenia in 2005, was recognized as "Excellent in Science" in 2017 by the Slovenian Research Agency, and received the Doctor Honoris Causa title in 2019 by the Azerbaijan State Agricultural University in Ganja, Azerbaijan, for his academic achievements.
Prof. Mauro Luciano Baesso received the degree in physics from State University of Maringá (UEM), Maringá, PR, Brazil, in 1984, and M.Sc. and Ph.D. degrees in photothermal sciences and optical materials from State University of Campinas, Campinas, SP, Brazil, in 1987 and 1990, respectively. His post-doctoral was in photothermal science at the Institute of Science and Technology (UMIST), University of Manchester, UK, 1992–1994. He was visiting professor in optoacoustic imaging at ETH-Zurich in 2020. From 1990 to date, he has been with the Department of Physics, UEM, first as a Lecturer, and then as a Full Professor, since 2009. He was one of the founders of the “Center for advanced studies in bio-photothermal and optical glass science/technology” of UEM. His research interests include Photoacoustic and Photothermal methods applied to biomedical science and optical materials with approach in multidisciplinary studies. He has authored and coauthored more than 400 technical papers, presented more than 30 invited talks at international conferences and supervised more than 80 students’.
Guenther Paltauf is an associate professor in experimental physics at the department of physics at the University of Graz, Austria. He received his Ph.D. in physics from the University of Graz in 1993. Later, he was visiting scientist at the University of Bern, Switzerland and the Oregon Medical Laser Center in Portland, OR. His research interests are photoacoustic imaging, photomechanical laser-tissue interactions and laser-ultrasonic characterization of materials. In the field of photoacoustic imaging, he is particularly interested in the development of special detection techniques of broadband ultrasound involving optical and piezoelectric sensors and in related image reconstruction methods.
Vincenzo Spagnolo works as Full Professor of Applied Physics at the Technical University of Bari. In 2019, he become Vice-Rector of the Technical University of Bari, deputy to Technology Transfer. The main scientific activity of Vincenzo Spagnolo has been related to electron-phonon interaction in low dimensional system, micro-probe optical characterization of semiconductor laser devices, thermal modelling of optoelectronic devices and more recently on the development of optoacoustic gas sensors based on quartz-enhanced photoacoustic spectroscopy. In 2021 he co-founded “PolySenSe Innovations”, a spinoff company devoted to commercialization of innovative gas sensors and consulting for applications in environmental, petrochemical, and biomedical fields. Prof. Spagnolo is program committee member of several SPIE and OSA conferences and editor of Sensors (MPDI), Applied Science (MPDI) and guest Editor of Photoacoustics (Elsevier) and Frontiers in Environmental Chemistry. He received the “Terra del Sole” prize and the “Re Manfredi” award in 2018, and the “Argos Hyppium” prize in 2019.