Modeling of the Low-Frequency Noise in Thermal Lens Spectrometry |
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| Authors: | Yolanda Martín-Biosca Claude Rozé Guillermo Ramis-Ramos |
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| Affiliation: | 1. Departament de Química Analítica, Facultat de Química, Universitat de València, 46100 Burjassot, Spain;2. Laboratoire d'Energétique des Systèmes et Procédés (LESP), Institut National des Sciences Appliquées (INSA) de Rouen, 76131 Mont-Saint-Aignan CEDEX, France |
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| Abstract: | The low-frequency noise observed in thermal lens spectrometry (TLS) can be modeled by assuming that the heated region, constituted by the thermal lens gradient and associated convective stream, behaves as a weakly damped harmonic oscillator with a natural frequency, vo, which is forced to move at an externally imposed pump frequency, vp. Out-of-phase lower-frequency oscillations of the TLS signal can be produced both by transient events, such as the beginning of the TLS experiment and small changes in the pump beam stability, and by drift of boundary conditions, such as the temperature of the surroundings. A model is developed and checked using 1-(2-pyridylazo)-2-napthol (PAN) solutions in silicone oil. Consequences of analytical interest are drawn; e.g., the signal-to-noise ratio of the TLS experiments is improved by pumping at the resonance frequency, where vp = vo. |
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