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VCSEL-based oxygen spectroscopy for structural analysis of pharmaceutical solids

Svensson, Tomas LU ; Andersson, Mats LU ; Rippe, Lars LU ; Svanberg, Sune LU ; Andersson-Engels, Stefan LU ; Johansson, Jonas and Folestad, Staffan (2008) In Applied Physics B 90(2). p.345-354
Abstract
We present a minimalistic and °exible single-beam instrumen-

tation based for sensitive tunable diode laser absorption spectroscopy (TD-

LAS) and its use in structural analysis of highly scattering pharmaceu-

tical solids. By utilising a vertical-cavity surface emitting laser (VCSEL)

for sensing of molecular oxygen dispersed in tablets, we address structural

properties such as porosity. Experiments involve working with unknown

pathlengths, severe backscattering and di®use light. These unusual experi-

mental conditions has lead to the use of the term gas in scattering media

absorption spectroscopy (GASMAS). By employing fully digital wavelength

modulation... (More)
We present a minimalistic and °exible single-beam instrumen-

tation based for sensitive tunable diode laser absorption spectroscopy (TD-

LAS) and its use in structural analysis of highly scattering pharmaceu-

tical solids. By utilising a vertical-cavity surface emitting laser (VCSEL)

for sensing of molecular oxygen dispersed in tablets, we address structural

properties such as porosity. Experiments involve working with unknown

pathlengths, severe backscattering and di®use light. These unusual experi-

mental conditions has lead to the use of the term gas in scattering media

absorption spectroscopy (GASMAS). By employing fully digital wavelength

modulation spectroscopy and coherent sampling, system sensitivity in am-

bient air experiments reaches the 10¡7 range. Oxygen absorption exhibited

by our tablets, being in°uenced by both sample porosity and scattering,

were in the range 8 £ 10¡5 to 2 £ 10¡3, and corresponds to 2-50 mm of

pathlength through ambient air (Leq). The day-to-day reproducibility was

on average 1.8% (0.3 mm Leq), being limited by mechanical positioning.

This is the ¯rst time sub-millimetre sensitivity is reached in GASMAS. We

also demonstrate measurements on gas transport on a 1 s timescale. By

employing pulsed illumination and time-correlated single photon counting,

we reveal that GASMAS exhibits excellent correlation with time-domain

photon migration. In addition, we introduce an optical measure of porosity

by relating oxygen absorption to average photon time-of-°ight. Finally, the

simplicity, robustness and low cost of this novel TDLAS instrumentation

provides industrial potential. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Applied Physics B
volume
90
issue
2
pages
345 - 354
publisher
Springer
external identifiers
  • wos:000252990900026
  • scopus:39149139306
ISSN
0946-2171
DOI
10.1007/s00340-007-2901-6
language
English
LU publication?
yes
id
75148ba5-0140-4096-96ee-0913fd6135be (old id 796066)
date added to LUP
2007-12-28 11:56:44
date last changed
2017-10-22 03:38:36
@article{75148ba5-0140-4096-96ee-0913fd6135be,
  abstract     = {We present a minimalistic and °exible single-beam instrumen-<br/><br>
tation based for sensitive tunable diode laser absorption spectroscopy (TD-<br/><br>
LAS) and its use in structural analysis of highly scattering pharmaceu-<br/><br>
tical solids. By utilising a vertical-cavity surface emitting laser (VCSEL)<br/><br>
for sensing of molecular oxygen dispersed in tablets, we address structural<br/><br>
properties such as porosity. Experiments involve working with unknown<br/><br>
pathlengths, severe backscattering and di®use light. These unusual experi-<br/><br>
mental conditions has lead to the use of the term gas in scattering media<br/><br>
absorption spectroscopy (GASMAS). By employing fully digital wavelength<br/><br>
modulation spectroscopy and coherent sampling, system sensitivity in am-<br/><br>
bient air experiments reaches the 10¡7 range. Oxygen absorption exhibited<br/><br>
by our tablets, being in°uenced by both sample porosity and scattering,<br/><br>
were in the range 8 £ 10¡5 to 2 £ 10¡3, and corresponds to 2-50 mm of<br/><br>
pathlength through ambient air (Leq). The day-to-day reproducibility was<br/><br>
on average 1.8% (0.3 mm Leq), being limited by mechanical positioning.<br/><br>
This is the ¯rst time sub-millimetre sensitivity is reached in GASMAS. We<br/><br>
also demonstrate measurements on gas transport on a 1 s timescale. By<br/><br>
employing pulsed illumination and time-correlated single photon counting,<br/><br>
we reveal that GASMAS exhibits excellent correlation with time-domain<br/><br>
photon migration. In addition, we introduce an optical measure of porosity<br/><br>
by relating oxygen absorption to average photon time-of-°ight. Finally, the<br/><br>
simplicity, robustness and low cost of this novel TDLAS instrumentation<br/><br>
provides industrial potential.},
  author       = {Svensson, Tomas and Andersson, Mats and Rippe, Lars and Svanberg, Sune and Andersson-Engels, Stefan and Johansson, Jonas and Folestad, Staffan},
  issn         = {0946-2171},
  language     = {eng},
  number       = {2},
  pages        = {345--354},
  publisher    = {Springer},
  series       = {Applied Physics B},
  title        = {VCSEL-based oxygen spectroscopy for structural analysis of pharmaceutical solids},
  url          = {http://dx.doi.org/10.1007/s00340-007-2901-6},
  volume       = {90},
  year         = {2008},
}