Observability of morphology-dependent output resonances in the Raman spectra of optically levitated microdroplets

Popp, Jürgen; Trunk, M.; Lankers, M.; Hartmann, Ingo; Schaschek, K.; Kiefer, W.

doi:10.1002/(sici)1097-4555(199707)28:7<531::aid-jrs133>3.0.co;2-i

Cited by 11 publications

(5 citation statements)

References 1 publication

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“…The WGMs are initially assigned guesses for polarity (TE or TM), mode order and mode number. 28,32,34,[36][37][38] The radius and dispersion corrected refractive index were then fitted to best match the theoretical WGM positions to those observed experimentally. The reported uncertainties on these fitted quantities are reported as one standard deviation (1σ) as determined from the least-squares fitting routine (Levenberg-Marquardt).…”

Section: Methodsmentioning

confidence: 99%

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

2016

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. (2016). Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation. RSC Advances: an international journal to further the chemical sciences, 6 (65), 60215-60222. Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation AbstractThis paper reports the performance of drop-on-demand piezo-activated microdroplet generation investigated using microdroplet cavity enhanced fluorescence spectroscopy. Aqueous microdroplets, doped with a fluorescent dye, exhibit fluorescence spectra that are dominated by cavity resonances (termed whispering gallery modes) that, when analysed using Mie theory, allow for the determination of the radius of each microdroplet. The effect of controlled changes in the square-wave droplet generator voltage waveform on droplet size is investigated as well as the size reproducibility of successive microdroplets. Furthermore, using custom square-wave waveforms, microdroplet radii spanning ∼10 to 30 μm are produced from the same droplet dispenser. These non-standard waveforms do not sacrifice the reproducibility of microdroplet generation with <1% size variation. Tuning the single square-wave pulsewidths induces predictable changes in the microdroplet radius and steps on the order of tens of nanometers are detectable. With finer voltage adjustments the microdroplet size is essentially tunable. These results confirm the extremely high stability and reproducibility of on-demand microdroplet generation and that precise size control is possible, rendering them suitable platforms for many applications in fundamental and applied research in areas including mass spectrometry, aerosol investigations and liquid-phase chemistry Aqueous microdroplets, doped with a fluorescent dye, exhibit fluorescence spectra that are dominated by cavity resonances (termed whispering gallery modes) that, when analysed using Mie theory, allow for the determination of the radius of each microdroplet. The effect of controlled changes in the square-wave droplet generator voltage waveform on droplet size is investigated as well as the size reproducibility of successive microdroplets. Furthermore, using custom square-wave waveforms, microdroplet radii spanning ~10 to 30 μm are produced from the same droplet dispenser. These non-standard waveforms do not sacrifice the reproducibility of microdroplet generation with <1% size variation. Tuning the single squarewave pulsewidths induces predictable changes in the microdroplet radius with steps on the order of tens of nanometers are detectable. With finer voltage adjustments the microdroplet size is essentially tunable. These results confirm the extremely high stability and reproducibility of on-demand microdroplet generation and that precise size control is possible, rendering them suitable platforms for many applications in fundamental and applied research in areas including mass spectrometry, aerosol investigations and liquid-phase chemistry.3

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Section: Methodsmentioning

confidence: 99%

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

2016

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“…111,118 Thus, broad Raman bands, such as that arising from excitation of the O-H stretching vibration of water, are composed of both a broad underlying band arising from spontaneous Raman scattering and resonant structure arising from stimulated Raman scattering. 116,117,[119][120][121] This is often referred to as cavity enhanced Raman spectroscopy (CERS). In addition to allowing the estimation of droplet size with sub-nanometre accuracy from droplets of known refractive index, the CERS fingerprint provides a unique signature of both the real part of the refractive index and the droplet size and both can be retrieved.…”

Section: Iib Characterising Single Particlesmentioning

confidence: 99%

Exploring the complexity of aerosol particle properties and processes using single particle techniques

2012

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The complex interplay of processes that govern the size, composition, phase and morphology of aerosol particles in the atmosphere is challenging to understand and model. Measurements on single aerosol particles (2 to 100 μm in diameter) held in electrodynamic, optical and acoustic traps or deposited on a surface can allow the individual processes to be studied in isolation under controlled laboratory conditions. In particular, measurements can now be made of particle size with unprecedented accuracy (sub-nanometre) and over a wide range of timescales (spanning from milliseconds to many days). The physical state of a particle can be unambiguously identified and its composition and phase can be resolved with a high degree of spatial resolution. In this review, we describe the advances made in our understanding of aerosol properties and processes from measurements made of phase behaviour, hygroscopic growth, morphology, vapour pressure and the kinetics of water transport for single particles. We also show that studies of the oxidative aging of single particles, although limited in number, can allow the interplay of these properties to be investigated. We conclude by considering the contributions that single particle measurements can continue to make to our understanding of the properties and processes occurring in atmospheric aerosol.

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“…Comparing the spectra from droplets against the spectra of calibrated bulk samples of sulfuric acid at known temperatures and concentrations will demonstrate whether or not it is justified to assume negligible heating by an intense laser source. As discussed by Popp et al 7 the change in temperature of a trapped droplet relative to ambient temperature could be caused by direct heating through absorption of laser light, enhanced heating due to input optical morphological resonance effects, [7][8][9] cooling due to evaporation of water from the droplet, or thermal conduction owing to temperature gradients near the droplet. There have been previous studies of droplet heating in laser traps, however these studies have either been limited to a very few droplets (,3), large uncertainties in the temperature, doubts about the temperature independence of the technique, or transient extreme heating by input morphological resonances.…”

Section: Introductionmentioning

confidence: 99%

“…Input and output morphological resonances are described in detail elsewhere. 8 Output morphological resonances of discrete wavelengths of the Raman signal can enhance the signal at these wavelengths in the phenomenon of cavity-enhanced Raman spectroscopy (CERS). [10][11][12][13] Morphological dependent resonances can also enhance the laser light interacting with the droplet, effectively increasing the path-length.…”

Section: Introductionmentioning

confidence: 99%

Laser heating of sulfuric acid droplets held in air by laser Raman tweezers

Hunt¹,

Ward²,

King³

2013

RSC Adv.

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An optical trap is used to hold a droplet of concentrated sulfuric acid in the focus of Ar-ion laser (l = 514.5 nm). The temperature and concentration of sulfuric acid in the droplet is calculated from the shifts and intensities of the Stokes-shifted Raman bands around 1000 rel.cm 21 . Aqueous sulfuric acid droplets can thus be used as a 'thermometer' for optically trapped droplets in air. It is demonstrated that the laser power can be kept low enough to prevent significant laser heating of the trapped droplet and that high laser powers (in excess of 16 mW) can result in heating of 5-10 uC.

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Observability of morphology-dependent output resonances in the Raman spectra of optically levitated microdroplets

Cited by 11 publications

References 1 publication

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

Exploring the complexity of aerosol particle properties and processes using single particle techniques

Laser heating of sulfuric acid droplets held in air by laser Raman tweezers

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