Effect of the Excitation Source on the Quantum-Yield Measurements of Rhodamine B Laser Dye Studied Using Thermal-Lens Technique

Abstract

Photothermal spectroscopy is a group of highly sensitive methods used to measure the optical absorption and thermal characteristics of a sample. [1][2][3] The basis of photothermal spectroscopy is a photo-induced change in the thermal state of the sample. The advantage of the photothermal technique is that it can be used to investigate the optical properties of materials that are unsuitable with traditional spectrophotometry. In fact, both thermal and fluorescence spectroscopy are complementary: thermal spectroscopy measures the photon energy, which has been converted to heat, while fluorescence spectroscopy observes re-emitted photons. When a medium is illuminated with laser radiation, some of the incident energy is absorbed by the molecules in the ground state, and becoming excited to higher energy states in the process. Following the absorption of a photon, any excess energy of a molecule can be dissipated in many ways.When the decay involves a radiationless process, localized temperature increases are produced, leading to heating of the sample. The thermal fluctuations produced by nonradiative relaxations may be probed optically, since the resulting density change also produces a change in the refractive index. Specifically, the transient refractive index forms an effective lens, which diverges the light as it passes through a sample. This phenomenon is called thermal lensing, and provides a nice example of laser spectroscopy.The fluorescence quantum yield (Qf), one of the key photophysical quantities, is a measure of the rate of nonradiative transitions that compete with the emission of light. The absolute values of Qf of organic laser dyes are practically important, because they are necessary to calculate thresholds for laser action. 4 Measurements based on photothermal effects are capable of giving absolute fluorescence yields of highly fluorescent solutions with high accuracy and reproducibility. In order to evaluate the absolute fluorescence efficiency, we must consider both radiative and nonradiative processes taking place in the medium. Because the contribution from nonradiative processes is not directly measurable using the traditional optical detection methods, thermo-optic techniques, such as photoacoustic (PA) and thermal lens (TL) spectroscopic methods, have been adopted for this purpose. 5,6 In this present study, the sensitivity and viability of photothermal lensing technique were exploited to determine the absolute fluorescence quantum yield of Rhodamine B (RhB) laser dye. The Qf values were found to be strongly influenced by different parameters, like environmental effects, concentration of the dye solution and type of excitation (cw or pulsed) source used for the thermal lens measurements. ExperimentalDetails of the experimental set up used for the cw thermal lens 7 and pulsed thermal lens 8 are given elsewhere. For a transient thermal lens, 532 nm radiation from a frequency-doubled Qswitched Nd:YAG laser (FWHM 9 ns) was used as the pump source to generate a thermal lens in the medium. A 632...

Computational Modelling for Efficient Transdentinal Drug Delivery

“…As reported by Bindhu and Harilal [24], the Rhodamine B quantum yield (up to φ = 0.97 at low concentrations) depends on the solvent and on the type of excitation (i.e., continuous or pulsed), while it weakly decreases with increasing concentration. Rhodamine B, dissolved in water, is most effectively excited by green light and emits red light with the maximum intensity in the range 575-585 nm [24,25].…”

“…Rhodamine B, dissolved in water, is most effectively excited by green light and emits red light with the maximum intensity in the range 575-585 nm [24,25]. Image processing and concentration calculations were performed using appropriate software (Flow Manager by Dantec Dynamics, Skovlunde, Denmark).…”

Significant Nusselt number increase in microchannels with a segmented flow of two immiscible liquids: An experimental study

“…In the case of Rhodamine B, the quantum efficiency is both concentration [20] and temperature dependent [19]. Thus, for a given dye concentration, the fluorescence can be related to temperature and used for thermometry.…”

Computational Modelling for Efficient Transdentinal Drug Delivery

“…As reported by Bindhu, C.V.,Harilal, S.S. [23] Rhodamine B quantum yield depends on the solvent and on the type of excitation (continuous, pulsed) and decreases weakly with increasing concentration. Rhodamine B, dissolved in water, is most effectively excited by green light and emits red light with the maximum intensity in the range 575-585 nm [23,24]. Image processing and concentration calculations were performed using appropriate software (Flow Manager by Dantec Dynamics).…”