Closed aperture CW Z-scan of L-tryptophan for determination of optical nonlinearity in the thermal regime

Abstract

The closed aperture continuous wave Z-scan of L-tryptophan at 661 nm was performed to investigate the variation of on-axis nonlinear phase shift ( Δ Φ 0 ) with the change of optical field strength. Δ Φ 0 was found to vary nonlinearly with irradiance ( I 0 ) in the range from 150 to 290 M W / m 2 . This nonlinear variation is explained by considering the effect of linear and nonlinear absorption of radiation on the thermo-optical refractive index. Using the quadratic fitting of Δ Φ 0 with I 0 , we have found the thermo-optic coefficient of refractive index d n / d T , thermal coefficient of nonlinear refractive index n 2 T , and the nonlinear absorption coefficient β in the observed power regime.

Investigating the Z-scan technique for quantifying circulating cell-free DNA (ccfDNA) extracted from blood plasma as a potential biomarker for various cancers

“…Observations indicate that both linear and nonlinear absorptions contribute to thermally generated nonlinear refraction in certain biomolecules [19]. The simplicity and cost-effectiveness of CW z-scan have elevated its status as a prominent nonlinear optical characterization method for biomaterials [20,21]. Diode lasers, known for their compactness, affordability, and controllable output power, are particularly suitable for investigating bio-samples, aiming to be employed as viable diagnostic tools.…”

“…Additionally, the noninvasive nature of this technique is noteworthy, as it necessitates only a small volume of blood sample, typically a few millilitres, from the patient. This technique utilizing CW diode laser have already been used in similar analysis involving inorganic, organic and bio samples establishing it as a reliable technique [20,[27][28][29][30].…”