Laser Heterodyne Measurement of Photothermal Displacement for Material Surface Characterization

Abstract

Summary: Double‐heterodyne photodisplacement technique (PDT), based on the detection of the thermal expansion of a sample under irradiation by laser light has been employed to improve the resolution of photothermal displacement measurements up to orders of sub‐picometers. We have developed an ultra‐sensitive system to measure photothermal displacement of metallic and non‐metallic materials, such as silicon, due to the illumination by an ordinary laser diode. Non‐destructive characteristics of the scheme are well suited for conditions that restrict access to the sample to be measured. Careful consideration is given to eliminate the noise sources, so as to achieve the level of sensitivity that needed to detect the structural inhomogeneity of materials. Good agreement between experimental results and theoretical predictions is demonstrated.Laser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.imageLaser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.

Investigation of ferromagnetic properties of LSMO nanolayers by laser modulated reflectance probe

“…Among nondestructive methods for investigation, optical methods are distinguished by the property to measure versatile physical parameters with high sensitivity unaffected by excessive electromagnetic fields. Layer thickness, optical indices and thermal properties determining the physical and chemical structures are assessable by the phase-sensitive interferometric methods like ellipsometry and laser heterodyne detection of photothermal displacement [1][2][3] . However, these methods are typically sophisticated and susceptible to random changes of the optical path causing inevitable vibration and depolarization noises.…”