High-resolution confocal fluorescence thermal imaging of tightly pumped microchip Nd:YAG laser ceramics

Abstract

A modified two-path confocal microscope was used to obtain fluorescence images of a Nd:YAG microchip element in the presence of a tightly focused 808 nm pump beam. Based on the temperature-induced homogeneous line broadening, high-resolution (<1 µm, <1°C) thermal images of the pump volume and surroundings were obtained from the spatial variation of Nd 3+ linewidth. Based on this direct, pure optical and non-contact method, thermal gradients as low as 0.02°C/µm were detected at focal volume, this being in agreement with theoretical predictions. The thermal imaging technique here presented opens the possibility of accurate compensation of thermal effects for the development of stable and efficient microchip lasers.High-resolution thermal imaging is one of the most challenging tasks that modern micro/nano technology is nowadays facing. This implies the achievement of thermal images with a spatial resolution better than 1 µm and, at the same time, with a thermal accuracy better than 1°C. Such images are nowadays required in a large number of applications ranging from biology (temperature is known to be one the key parameters determining cell and tissue dynamics) [1, 2], to micro/nano electronics (where the detection of hot-points is a crucial issue toward the optimization of integrated circuits) [3,4]. In addition to all these fields, thermal imaging is also being required by photonics, especially

Nd:YAG Near‐Infrared Luminescent Nanothermometers

“…In a typical synthesis, yttrium nitrate [Alfa AEesar Y(NO 3 b) Time evolution of the subtissue temperature determined from the ratio between the intensities of the two emission peaks. In a typical synthesis, yttrium nitrate [Alfa AEesar Y(NO 3 b) Time evolution of the subtissue temperature determined from the ratio between the intensities of the two emission peaks.…”

“…[ 3 ] This is of special interest in areas such as micro/nanoelectronics (where temperature singularities at the submicrometric scale constitute one of the fi rst signs of fatal failure) [ 4 ] and biological applications, as temperature plays an essential role in the dynamics of biological systems. The use of high numerical aperture (NA) optics for both optical excitation and luminescence collection allows for remote thermal reading with submicrometric spatial resolution.…”

“…The use of high numerical aperture (NA) optics for both optical excitation and luminescence collection allows for remote thermal reading with submicrometric spatial resolution. [ 3 ] This is of special interest in areas such as micro/nanoelectronics (where temperature singularities at the submicrometric scale constitute one of the fi rst signs of fatal failure) [ 4 ] and biological applications, as temperature plays an essential role in the dynamics of biological systems. [ 5 ] Thus, high-resolution temperature sensing can be used as an early diagnosis tool, as many diseases, including cancer and infl ammatory processes, lead to the appearance of relevant temperature singularities even at their early stages.…”

“…Consequently, neodymium ions offer the possibility of deep-tissue luminescence imaging and thermal sensing, as has already been demonstrated. [ 3 ] Despite the encouraging results obtained in bulk Nd:YAG, the use of Nd:YAG nanoparticles for high brightness luminescence nanothermometry has not yet been reported. [ 27,28 ] Nd:YAG bulk crystal also appears to be capable of thermal sensing based on the analysis of its two hypersensitive luminescence lines located near 940 nm, which correspond to the transitions between the two Stark levels of the 4 F 3/2 metastable state to the highest energy level of the 4 I 9/2 state.…”

“…[ 27 ] These two lines have been investigated for thermal imaging of Nd:YAG microchip lasers. [ 3 ] Despite the encouraging results obtained in bulk Nd:YAG, the use of Nd:YAG nanoparticles for high brightness luminescence nanothermometry has not yet been reported. The transition from bulk to nano in the case of the Nd:YAG systems is challenging as preserving the outstanding properties of the bulk material in the synthesis of Nd:YAG nanoparticles is not an easy task.…”