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This study aimed to investigate the effects of thermal annealing on a film of squaraine (SQ) molecules in a polymethyl methacrylate (PMMA) matrix. Molecular aggregation is inferred from in situ absorption measurements, and excited state dynamics are measured using a spatially encoded transient absorption (TA) spectroscopy. TA spectra were well-replicated using a kinetic model that evolves as a function of annealing time and extent of aggregation. While linear absorbance spectra indicate that the SQ molecules are primarily uncoupled or weakly-coupled when initially deposited in a PMMA matrix, the kinetic model shows that some pi-stacked aggregates are already present. Excitons are funnelled by energy transfer to these aggregates in just a few picoseconds. The amount of pi-stacked aggregates increases during thermal annealing, further increasing the population of excitons that end up in these aggregates.
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This content will become publicly available on May 1, 2026
H 2 O absorption spectroscopy via focused laser differential interferometry
A modification of focused laser differential interferometry (FLDI) is demonstrated with an infrared tunable diode laser (TDL) to achieve simultaneous absorption spectroscopy (AS) measurements. Measurements from this absorbing-FLDI (A-FLDI) are shown for a Hencken burner plume. Initial comparison measurements are recorded using TDLAS and an electrical hygrometer. Raw voltage and estimated absorbance measurements illustrate that the technique detects five distinct absorbance peaks of the methane–air flame while retaining the expected behavior of typical FLDI. This modification furthers efforts to enable FLDI to conduct analysis of the pressures, temperatures, and molecular densities of flows. It also explores the potential for reducing path-integration (PI) effects in absorption spectroscopy and potentially enabling spatially and temporally resolved local flow measurements. Reductions in PI length as high as 82%–84% are observed.
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- Award ID(s):
- 2409331
- PAR ID:
- 10587009
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Applied Optics
- Volume:
- 64
- Issue:
- 14
- ISSN:
- 1559-128X; APOPAI
- Format(s):
- Medium: X Size: Article No. 3856
- Size(s):
- Article No. 3856
- Sponsoring Org:
- National Science Foundation
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