Time-resolved thermal lens calorimetry

Accuracy of Measurements of Thermophysical Parameters by Dual-Beam Thermal-Lens Spectrometry

Thermal-lens spectrometry is a sensitive technique for determination of physicochemical properties and thermophysical parameters of various materials including heterogeneous systems and nanoparticles. In this paper, we consider the issues of the correctness (trueness) of measurements of the characteristic time of the thermal-lens effect and, thus, of the thermal diffusivity determined by dual-beam mode-mismatching thermal lensing. As sources of systematic errors, major factors-radiation sources, sample-cell and detector parameters, and general measurement parameters-are considered using several configurations of the thermal-lens setups, and their contributions are quantified or estimated. Furthermore, with aqueous ferroin and Sudan I in ethanol as inert colorants, the effects of the intermolecular distance of the absorbing substance on the correctness of finding the thermophysical parameters are considered. The recommendations for checking the operation of the thermal-lens setup to ensure the maximum accuracy are given. The results obtained help reducing the impact of each investigated factor on the value of systematic error and correctly measure the thermophysical parameters using thermal-lens spectrometry.

Thermal diffusivity imaging with the thermal lens microscope

A coaxial thermal lens microscope was used to generate images based on both the absorbance and thermal diffusivity of histological samples. A pump beam was modulated at frequencies ranging from 50 kHz to 5 MHz using an acousto-optic modulator. The pump and a CW probe beam were combined with a dichroic mirror, directed into an inverted microscope, and focused onto the specimen. The change in the transmitted probe beam's center intensity was detected with a photodiode. The photodiode's signal and a reference signal from the modulator were sent to a high-speed lock-in amplifier. The in-phase and quadrature signals were recorded as a sample was translated through the focused beams and used to generate images based on the amplitude and phase of the lock-in amplifier's signal. The amplitude is related to the absorbance and the phase is related to the thermal diffusivity of the sample. Thin sections of stained liver and bone tissues were imaged; the contrast and signal-to-noise ratio of the phase image was highest at frequencies from 0.1-1 MHz and dropped at higher frequencies. The spatial resolution was 2.5 μm for both amplitude and phase images, limited by the pump beam spot size.

Laser induced-thermal lens spectrometry after cloud point extraction for the determination of trace amounts of palladium

Cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS) has been developed for the preconcentration and determination of palladium. TLS and CPE methods have good matching conditions for the combination because TLS is a suitable method for the analysis of low volume samples obtained after CPE. Palladium was complexed with 1-(2-pyridylazo)-2-naphthol (PAN) as a complexing agent in an aqueous medium and concentrated by octylphenoxypolyethoxyethanol (Triton X-114) as a surfactant. After the phase separation at 60 degrees C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 microL of carbon tetrachloride. The obtained solution was introduced into a quartz microcell and the analyte was determined by laser induced-thermal lens spectrometry (LI-TLS). The single-laser TLS was used as a sensitive method for the determination of palladium-PAN complex in 20 microL of the sample. Under optimum conditions, the analytical curve was linear for the concentration range of 0.3-60 ng mL(-1) and the detection limit was 0.04 ng mL(-1). The enhancement factor of 460 was achieved for 10 mL samples containing the analyte and relative standard deviations were lower than 5%. The developed method was successfully applied to the extraction and determination of palladium in water samples.

Ultrasensitive thermal lens spectroscopy of water

A recently developed dual-beam configuration that optimizes the thermal lens technique has been used to obtain the absorption spectrum of pure water from 350 to 528 nm. Our results indicate the minimum linear absorption coefficient smaller than 2 x 10(-5) cm(-1) between 360 and 400 nm. This value is lower than previous literature data, and it is blueshifted. Absorption coefficients as small as 2 x 10(-7) cm(-1) can be measured for water using 1 W of excitation power. A detection limit of approximately 6 x 10(-9) cm(-1)(P=1 W) for CCl(4) was estimated, which represents, to the best of our knowledge, the highest sensitivity obtained in small absorption measurements in liquids.

Laser induced thermal lens spectrometry for cobalt determination after cloud point extraction

A new approach, employing cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS), has been developed for the determination of cobalt. The CPE and TLS methods have good matching conditions for combination because TLS is suitable for low volume samples obtained after CPE and for organic solvents, which are used for dissolving the remaining analyte phase. 1-(2-Pyridylazo)-2-naphthol (PAN) was used as a complexing agent and octylphenoxypolyethoxyethanol (Triton X-114) was added as a surfactant; then the pH of solution was adjusted. After phase separation at 50 degrees C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 microL of carbon tetrachloride. The obtained solution was introduced into the quartz micro cell and the analyte was determined by thermal lens spectrometry. The He-Ne laser (632.8 nm) was used as both the probe and the excite source. Under optimum conditions, the analytical curve was linear for the concentration range of 0.2-40 ng mL(-1) and the detection limit was 0.03 ng mL(-1). The enhancement factor of 470 was achieved for a 10 mL sample. Relative standard deviations were lower than 5%. The method was successfully applied to the extraction and determination of cobalt in tap, river and sea water.

Development of a scanning microscopy by total internal reflection coupled with thermal lens spectroscopy

Non-destructive measurement of a small region on a solid/liquid interface is of great importance in physical chemistry and biochemistry, especially in the research of thin films and cell membranes. Optical methods for surface analysis with high lateral resolution are suitable methods for monitoring them. We now report a new scanning optical microscopic method to which total internal reflection coupled with a thermal lens technique was introduced. Its lateral resolution was estimated both experimentally and theoretically. To experimentally estimate the resolution, the grid patterns of thin photoresist films with well-defined lateral structures were measured. The experimental resolution was about 45 microm, which was almost same as the diameter of the excitation beam at a glass/sample interface. From this result, it was verified that this new scanning microscopy ideally worked.

Thermal lens spectrometry in biochemical analysis

The photothermal spectroscopic techniques, with special emphasis on the thermal lens spectrometry (TLS), are introduced to the non-specialist in laser spectroscopy. The following topics are treated on an elementary basis: fundamentals and analytical characteristics, instrumentation, selectivity and multi-wavelength capability, the models describing the signal-concentration relationship, the sensitivity, background noise and limits of detection, the influence of light scattering and flow. Applications related to the fields of clinical and biochemical analysis and organic pollution are given. The thermal lens circular dichroism and the infrared TLS are also briefly outlined.

Submicrometer resolution images of absorbance and thermal diffusivity with the photothermal microscope

The photothermal microscope is a laser-based technique which utilizes the crossed-beam thermal lens to measure simultaneously both absorbance and thermal diffusivity within small probe volumes. The microscope provides images with spatial resolution better than 1microm(3) in a simple optical design. High resolution images of histological and botanical samples are presented.

Thermooptic-based differential measurements of weak solute absorptions with an interferometer

An interferometric method of measuring small differences between weak optical absorptions of solutions has been developed using the thermooptic effect. To record the small changes in optical path length ~lambda/200 due to heating, it was necessary to stabilize the fringe pattern with respect to slow thermal drift using a galvanometer-driven compensator plate controlled by a closed feedback loop. Fringe shifts from background absorptions were nulled out to better than 1 part in 400, permitting the measurement of differences in absorptions between two solutions that were l/100th of background. Using laser powers of 100 mW, absorptions approximately 5 x 10(-6) cm(-1) (base e) could be measured with CC1(4) solutions.

Use of the thermal lens technique to measure the luminescent quantum yields of dyes in PMMA for luminescent solar concentrators

The thermal lens technique has been used to measure absolute luminescent quantum yields of dyes in liquid and solid (PMMA) solutions. The validity of the approach has been established by measuring quantum yields of known compounds, and we stress the application to dye/polymer systems that would be suitable for luminescent solar concentrators. Our results for rhodamine 6G and Fluorol 555 give 0.93 +/- 0.04 and 0.88 +/- 0.03, respectively, for their quantum yield in PMMA.

Thermally induced laser pulsing to measure weak optical absorptions

Intracavity thermal lensing has been used to convert a cw dye laser to pulsed operation. The pulse width is a measure of the absorptivity of the solution in the cell. Experimental data are presented to show how this technique can be used to measure the absorptivity of a pure solvent and the concentration of a solute. The absorptivities (base e) of water, CH(3)OH, CH(3)COCH(3), and CCl(4) were determined to be, respectively, (1.24 +/- 0.17) x 10(-3), (1.01 +/- 0.07) x 10(-3), (1.74 +/- 0.09) x 10(-4), and (3.95 +/- x(-6) cm(-1). For CCl(4) in a 10-cm sample cell, the minimum detectable absorptivity is ~4 x 10(-6) cm(-1).