Thermal lens microscope sensitivity enhancement using a passive Fabry–Perot-type optical cavity

Abstract

We developed a thermal lens microscope equipped with a passive optical cavity, which provides an optical feedback for the multiple pass of the probe laser beam to enhance sensitivity. Considering the maximum absorption peak for Fe(II) at 532 nm wavelength, we have achieved a 6.6-fold decrease in the limit of detection (LOD) to a level of 0.077 μg • l −1 without a cavity. The possibilities to use thermal lens detection combined with an optical resonator was proposed and a drastic thermal lens signal enhancement was achieved using very low excitation power. The corresponding LOD for Fe(II) was further decreased to the level of 0.006 μg • l −1 which represents an 85-fold decrease of the LOD value. This setup is a promising device, which can be applied as a sensitive tool for detecting chemical traces in small volumes of solutions.

Absorption Spectra of Ethanol and Water Using a Photothermal Lens Spectrophotometer

“…The TL signal, in the steady-state situation, is defined as the relative change of the PL beam intensity 1 where I 0 is the beam intensity transmittance of the PL beam onto the detector when the sample is not irradiated ( t = 0) by the LS, I is the corresponding intensity transmittance near the steady-state situation when the sample is being irradiated. For the particular configuration when the LS is focused and the PL is highly collimated and expanded, the TL signal, in case of four passes of the PL through the sample (details of such configuration are presented in the experimental part), can be expressed by 6,16 …”

“…As a result of the multiple passes of the PL through the sample, the method dramatically increases the optical path length. 16 This increased path length through the sample significantly improves the measurement sensitivity of the technique giving the possibility of highly sensitive scattering-free measurements in semitransparent liquids.…”

Thermal lensing: outside of the lasing medium

“…A TLM with enhanced sensitivity has been designed also by Cabrera et al in [72]. The authors used a passive Fabry-Perot optical cavity in which the sample studied was placed.…”

A comparison between thermal lens and conventional optical spectroscopy for monitoring of a photocatalytic process

“…The consequent intensity changes in the probe beam are measured by a photodiode and provide the thermal lens signal. Among other applications, TLS has been widely used for sensitive detection of a wide class of species dissolved in dissimilar media [1][2][3][4][5][6][7][8][9] and for the study of different photodegradation processes [4,5]. When the excitation beam is highly focused onto a micrometric region of the sample the technique is called thermal lens microscopy (TLM), with the main advantage that very low amounts of samples can be characterized [6].…”