Richard D. Snook

A model for cw laser induced mode-mismatched dual-beam thermal lens spectrometry

Abstract Thermal lens spectrometry is a highly sensitive technique for chemical analysis of solutions. The mode-mismatched dual-beam method is more sensitive than the mode-matched dual-beam or single beam method. Unfortunately, there is no theoretical model for the cw laser induced mode-mismatched dual-beam method. In this paper, taking the aberrant nature of thermal lens into account a theoretical model for cw laser induced thermal lens spectrometry is presented. The model is suitable for mode-mismatched, mode-matched dual-beam and single-beam methods. The model is of simple mathematical expression and convenient to use for both steady-state measurements and time-resolved techniques. Experimental proofs of the model are presented and found to be in good agreement.

Mode‐mismatched thermal lens determination of temperature coefficient of optical path length in soda lime glass at different wavelengths

The time‐resolved and steady‐state mode‐mismatched thermal lens technique has been used to determine the temperature coefficient of optical path length ds/dT at different wavelengths of soda lime glasses (72 wt % SiO2, 18 wt % Na2O, 10 wt % CaO, and 70.5 wt % SiO2, 17.5 wt % Na2O, 10 wt % CaO, 2 wt % Fe2O3). The aberrant model, which takes into account the thickness change of the sample and is more realistic than the parabolic treatment when used to describe the thermal lens effect, was used as the theoretical model. The results showed that ds/dT is (2.1±0.1)×10−6 K−1 at 632.8 nm and (2.4±0.1)×10−6 K−1 at 442 nm for the undoped sample and (4.66±0.03)×10−6 K−1 at 632.8 nm and (6.1±0.1)×10−6 K−1 at 442 nm for the iron‐doped sample. The greater value of this parameter found for the doped sample at the absorption band (442 nm) was associated with the bigger value of the temperature coefficient of the electronic polarizability caused by the presence and environment of Fe3+ iron in the structure of the glass.

Measurement of elastic properties of prostate cancer cells using AFM

This communication reports that three prostate cancer cells of differing metastatic potential were discriminated based on their Youngs moduli (LNCaP - 287 +/- 52 N m(-2), PC-3 - 1401 +/- 162 N m(-2) and BPH - 2797 +/- 491 N m(-2)) which were determined using AFM and the Hertz model.

Thermal lens spectrometry. A review

This review considers the technique of thermal lens spectrometry and its applications to chemical measurements in solid, liquid and gaseous phases. Practical applications, theoretical treatments and instrumental developments are considered in terms of their analytical use and potential.

Three‐dimensional model for cw laser‐induced mode‐mismatched dual‐beam thermal lens spectrometry and time‐resolved measurements of thin‐film samples

Conventional thermal lens spectrometry theory assumes that the sample is an infinite medium, and only the radial temperature rise and heat flow in the sample are considered. This approach is not suitable for thin‐film samples. Considering the axial boundary conditions of the sample, a three‐dimensional model for cw laser‐induced mode‐mismatched thermal lens spectrometry is presented. However, its mathematical expression is not so convenient as that of the conventional theory to deal with the experimental data. The model shows that, besides axial boundary conditions of the sample, the ratio of excitation laser spot size to the sample thickness ωe/l is a crucial parameter to minimize the axial heat flow. By choosing small ωe/l, it is possible for the conventional theory to describe the development of the thermal lens of a thin sample for a short duration. Experimental proofs for the theoretical prediction are made, and good agreements are achieved.

Time-resolved thermal lens measurement of thermal diffusivity of soda—lime glass

Abstract The time-resolved mode-mismatched thermal lens technique has been used to determine a precise value for the absolute thermal diffusivity of soda—lime glass (70.5 wt% SiO2, 17.5 wt% Na2O, 10 wt% CaO and 2 wt% Fe2O3). The thermal diffusivity was found to be (4.9±0.3) × 10−3 cm2/s which is in good agreement with the value obtained by photoacoustic spectrometry ((5.1±0.1) × 10−3 cm2/s). The technique is non-contacting and non-destructive.

Thermal lens measurement of absolute quantum yields using quenched fluorescent samples as references

Abstract The thermal lens technique has been used to determine precise values for the quantum yield of sodium fluorescein in 0.1 M NaOH at concentrations below 10−5 M. Samples of sodium fluorescein are used as reference absorbers, The quantum yield was determined to be 0.92±0.03.

Spectral discrimination of live prostate and bladder cancer cell lines using Raman optical tweezers

An investigation into the use of Raman optical tweezers to study urological cell lines is reported, with the ultimate aim of determining the presence of malignant CaP cells in urine and peripheral fluids. To this end, we trapped and analyzed live CaP cells (PC-3) and bladder cells (MGH-U1), because both prostate and bladder cells are likely to be present in urine. The laser excitation wavelength of 514.5 nm was used, with Raman light collected both in back- and forward-scattering geometric configurations. For the backscattering configuration the same laser was used for trapping and excitation, while for forward scattering a 1064 nm laser provided the trapping beam. Analysis of cell-diameter distributions for cells analyzed suggested normal distribution of cell sizes, indicating an unbiased cell-selection criterion. Principal components analysis afforded discrimination of MGH-U1 and PC-3 spectra collected in either configuration, demonstrating that it is possible to trap, analyze, and differentiate PC-3 from MGH-U1 cells using a 514.5 nm laser. By loading plot analysis, possible biomolecules responsible for discrimination in both configurations were determined. Finally, the effect of cell size on discrimination was investigated, with results indicating that separation is based predominantly on cell type rather than cell size.

Factors influencing the discrimination and classification of prostate cancer cell lines by FTIR microspectroscopy

In this study we obtained Fourier transform infrared (FTIR) spectra of fixed prostate cell lines of differing types as well as the primary epithelial cells from benign prostatic hyperplasia (BPH). Results showed that by using multivariate chemometric analysis it was possible to discriminate and classify these cell lines, which gave rise to sensitivity and specificity values of >94% and >98%, respectively. Following on from these results the possible influences of different factors on the discrimination and classification of the prostate cell lines were examined. Firstly, the effect of using different growth media during cell culturing was investigated, with results indicating that this did not influence chemometric discrimination. Secondly, differences in the nucleus-to-cytoplasm (N/C) ratio were examined, and it was concluded that this factor was not the main reason for the discrimination and classification of the prostate cancer (CaP) cell lines. In conclusion, given the fact that neither growth media nor N/C ratio could totally explain the classification it is likely that actual biochemical differences between the cell lines is the major contributing factor.

A model for cw laser induced mode‐mismatched dual‐beam thermal lens spectrometry based on probe beam profile image detection

A model for cw laser induced mode‐mismatched dual‐beam thermal lens spectrometry using probe beam profile detection has been developed. This model exhibits the following behavior: after passing through the thermal lens the TEM00 Gaussian probe beam becomes the superposition of several Gaussian beams of different parameters. This model has a compact mathematical expression, for which experimental proofs are given.