Linear Raman spectroscopy on aqueous aerosols: influence of nonlinear effects on detection limits

Vehring, Reinhard

doi:10.1016/s0021-8502(97)00292-9

Cited by 22 publications

(17 citation statements)

References 70 publications

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“…Unfortunately, the models for the calculation of the SRS threshold respectively, the gain enhancement in droplets given by Schweiger, 6 Lin and Campillo 11 and Vehring 12 does not contain any consideration of the excitation pulse form or duration. However, different experimental research was done for the determination of the photon lifetime in droplets.…”

Section: Resultsmentioning

confidence: 99%

“…Additionally, the seeding of the laser and thereby, the avoidance of temporal spikes in the origin laser pulse can potentially increase the SRS threshold. The droplet cavity quality can be reduced by the decrease of the ratio of the refraction index of the liquid and the environment 9 or by absorption of the excitation light in the droplets by a dye 12,14 , by induced or random imperfections of the droplet surface. Other recommendations that can be found in the literature are, for example, the use of broadband laser sources or ultra short (picosecond) laser excitation.…”

Section: Resultsmentioning

confidence: 99%

“…Lin and Campillo 11 published their measured thresholds which correlate strongly to a radius size dependence r 4 and account the additional potency of 2 to quantum electrodynamic enhancement (QED) of the cavity gains. Vehring 12 published the SRS threshold in micro-droplets of distilled water and the results showed no remarkable increase in the droplet size. In spray measurements the droplet size depends on the nozzle geometry, the fluid, the temperature of the fluid and the surrounding and the injection pressure.…”

Section: Introductionmentioning

confidence: 99%

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Dependence of the stimulated Raman scattering threshold in droplets on the temporal stretching of a nanosecond laser pulse

Malarski

Leipertz

2008

J Raman Spectroscopy

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For linear Raman spectroscopy in micro-droplets the excitation laser energy and therefore the signal strength is limited either by the threshold for the excitation of nonlinear processes in the droplets or by the generation of a plasma (gas breakdown) in the vicinity of the droplets. These processes are due to the enhancement of the excitation field by morphology-dependent resonances (MDRs) which are built up in the cavity synthesised by the droplets. As these stimulated signals disturb the detection of the linear signal it is of high interest for different applications to suppress the stimulated Raman scattering (SRS) or to use an excitation intensity below the SRS threshold with a sufficiently large integrated laser energy to obtain an appropriate signal-to-noise ratio for the linear Raman process. In this paper the effect of temporal stretching of the incoming laser pulse with the help of an optical pulse stretcher on the SRS threshold is described and discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dependence of the stimulated Raman scattering threshold in droplets on the temporal stretching of a nanosecond laser pulse

Malarski

Leipertz

2008

J Raman Spectroscopy

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“…Stimulated Raman scattering has been used to characterize aqueous aerosols by linear Raman spectroscopy. 144 Scanning near-IR Raman microscopy has been successfully used to map aerosol particulate deposits on the stages of an Anderson cascade impactor (ACI), as shown in Figure 9, from a combination pressurized MDI (pMDI), Ventide. 145 ACI is the standard in vitro model of aerosol deposition in the lungs.…”

Section: E8mentioning

confidence: 99%

Raman characterization and chemical imaging of biocolloidal self-assemblies, drug delivery systems, and pulmonary inhalation aerosols: A review

Mansour

Hickey

2007

AAPS PharmSciTech

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This review presents an introduction to Raman scattering and describes the various Raman spectroscopy, Raman microscopy, and chemical imaging techniques that have demonstrated utility in biocolloidal self-assemblies, pharmaceutical drug delivery systems, and pulmonary research applications. Recent Raman applications to pharmaceutical aerosols in the context of pulmonary inhalation aerosol delivery are discussed. The "molecular fingerprint" insight that Raman applications provide includes molecular structure, drug-carrier/ excipient interactions, intramolecular and intermolecular bonding, surface structure, surface and interfacial interactions, and the functional groups involved therein. The molecular, surface, and interfacial properties that Raman characterization can provide are particularly important in respirable pharmaceutical powders, as these particles possess a higher surface-area-to-volume ratio; hence, understanding the nature of these solid surfaces can enable their manipulation and tailoring for functionality at the nanometer level for targeted pulmonary delivery and deposition. Moreover, Raman mapping of aerosols at the micro-and nanometer level of resolution is achievable with new, sophisticated, commercially available Raman microspectroscopy techniques. This noninvasive, highly versatile analytical and imaging technique exhibits vast potential for in vitro and in vivo molecular investigations of pulmonary aerosol delivery, lung deposition, and pulmonary cellular drug uptake and disposition in unfixed living pulmonary cells.

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“…Laboratory measurements of Raman spectra from levitated microspheres have been performed by numerous investigators [Vehring et al, 1995Schweiger, 1991;Buehler et al, 1991;Bazile and Stepowski, 1994;Vehring, 1998]. These experiments have been performed over various size parameter ranges, where size parameter is defined as the circumference of the sphere divided by the input wavelength.…”

Section: Theory: Raman Scattering From Spheresmentioning

confidence: 99%

Cloud liquid water, mean droplet radius, and number density measurements using a Raman lidar

Whiteman¹,

Melfi²

1999

J. Geophys. Res.

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Abstract. A new technique for measuring cloud liquid water, mean droplet radius, and droplet number density is outlined. The technique is based on simultaneously measuring Raman and Mie scattering from cloud liquid droplets using a Raman lidar. Laboratory experiments on liquid microspheres have shown that the intensity of Raman scattering is proportional to the amount of liquid present in the spheres. This fact is used as a constraint on calculated Mie intensity assuming a gamma function particle size distribution. The resulting retrieval technique is shown to give stable solutions with no false minima. It is tested using Raman lidar data where the liquid water signal was seen as an enhancement to the water vapor signal. The general relationship of retrieved average radius and number density is consistent with traditional cloud physics models. Sensitivity to the assumed maximum cloud liquid water amount and the water vapor mixing ratio calibration are tested. Improvements to the technique are suggested.

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Linear Raman spectroscopy on aqueous aerosols: influence of nonlinear effects on detection limits

Cited by 22 publications

References 70 publications

Dependence of the stimulated Raman scattering threshold in droplets on the temporal stretching of a nanosecond laser pulse

Dependence of the stimulated Raman scattering threshold in droplets on the temporal stretching of a nanosecond laser pulse

Raman characterization and chemical imaging of biocolloidal self-assemblies, drug delivery systems, and pulmonary inhalation aerosols: A review

Cloud liquid water, mean droplet radius, and number density measurements using a Raman lidar

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