Recherche dans les collections de brevets nationales et internationales
Une partie du contenu de cette demande n'est pas disponible pour le moment.
Si cette situation persiste, contactez-nous auObservations et contact
1. (WO1986004140) PROCEDE ET APPAREIL POUR ANALYSER DES SUSPENSIONS GAZEUSES CONTENANT DES PARTICULES
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

THE CLAIMS
Having thus described the invention, what is claimed is:

1. In apparatus for the analysis of a gaseous suspension of liquid particles, solid particles, or both, the combination comprising:
(a) interferometer means operatively
positionable with respect to the suspension for encoding radiation projected thereinto and
radiation emanating therefrom;
(b) means operatively positionable with respect to the suspension and said interferometer means for collecting coded radiation from the suspension, said collecting means being adapted to discriminate radiation transmitted through the suspension from radiation emanating therefrom, such emanating radiation including any radiation
scattered by the particles;
(c) source means for providing an
electromagnetic radiation beam and for projecting it through said interferometer means for coding thereby and for transmission through the
suspension; and
(d) electronic data processing means for analyzing the radiation collected by said
collecting means.
2. The apparatus of Claim 1 wherein said collecting means comprises a first collector operatively positionable for collecting radiation transmitted through the suspension, and a second collector, separate from said first collector, operatively positionable for collecting radiation emanating therefrom.
3. The apparatus of Claim 2 adapted for use with containment means which has a sidewall defining a chamber for the containment of the gaseous suspension to be analyzed, the sidewall in turn having at least one port providing optical access into the chamber thereof, said second collector, and at least one of said source means and said first collector, being disposed on said apparatus for positioning with respect to the one port so as to function therethrough.
4. The apparatus of Claim 3 additionally including means defining an aperture of variable size from which passes the transmitted radiation collected by said first collector, the capability of said apparatus for making determinations of the size of the particles of the suspension thereby being improved.
5. The apparatus of Claim 3 adapted for use with such containment means having a pair of optical access ports aligned transversely on opposite sides of the sidewall thereof, said source means and said first collector being in effective optical alignment with and spaced from one- another to accommodate the containment means therebetween, so as to permit projection of the beam from said source means through the aligned access ports to said first collector.

6. The apparatus of Claim 3 additionally including a cell cooperatively providing such containment means as an integral component of said apparatus, and means for providing a substantially homogeneous gaseous suspension thereto.
7. The apparatus of Claim 6 wherein said cell has a generally cylindrical sidewall and end walls cooperatively defining said chamber thereof, said sidewall having a pair of access ports positioned diametrically thereon, and said end walls having means defining inlet and outlet channels therethrough, aligned substantially on the longitudinal axis of said cell, for the injection and removal of particles thereinto and therefrom, respectively, said means for providing the suspension including said inlet channel, said cell also having means by which the temperature of the inside surface of said sidewall, and the temperature of said inlet and outlet channel defining means, can be independently controlled.
8. The apparatus of Claim 7 wherein said inlet channel is adapted to inject said particles as a monodispersed stream.
9. The apparatus of Claim 2 wherein said second collector is effectively disposed along the path of radiation between said source means and said interfermometer, and wherein said apparatus additionally includes diverter means disposed for establishing a radiation path between the suspension and either said source means, said second collector, or both.
10. The apparatus of Claim 9 wherein said diverter means is operative to either permit passage of radiation from said source means to the suspension, or to block such passage of radiation while simultaneously directing radiation from the suspension to said second collecting means, whereby measurements of radiation transmitted through and emanating from the suspension, respectively, can be selectively made.
11. The apparatus of Claim 9 wherein said diverter means is adapted to simultaneously permit passage of radiation from said source means to the suspension while directing radiation therefrom to said second collecting means, said diverter means having a first portion which is transparent to the radiation from said source means and a second portion which is opaque thereto and is reflective of radiation emanating from the suspension and directed theretoward, whereby such transmitted and emanating radiation can simultaneously be measured using said first and second collecting means, respectively.

12. The apparatus of Claim 1 comprising a Fourier-transform spectrometer, wherein said spectrometer is adapted to develop a spectrum representative of the intensity of the collected radiation as a function of wavenumber, and wherein said data processing means thereof is programmed to compare the representative spectrum to preestablished spectra indicative of a parameter for which the gaseous suspension is being analyzed, so as to fit the representative spectrum thereto and thereby determine the parameter.
13. The apparatus of Claim 12 wherein said source means provides radiation of wavelengths in the infrared region, and wherein said data processing means is programmed to effect said comparison by application of at least one of the following basic equation, generalized formulae, and equations derived therefrom:

..L
E -f J [{ksBB(Ts) + k BB(T ) + NAζBB(T ) +
o
NAQSBB(TW)} exp(-y)]dl.

wherein "y" is the integra '

Ξ =
[kgBB(Ts) +kgBB(Tg) +NA BB(Tp) +NAQgBB(Tw) ]- [1-exp (- (ks+kg+NAQeχt) ) ]

ks +kg + NAQext
and
(1- = l-exp[-(ks + kg + NAQeχt)L];
wherein:

E - represents any collected radiation emanating from the gaseous suspension and not transmitted therethrough,
- represents the ratio of any collected radiation that is transmitted through the suspension, divided by radiation that would be transmitted in the absence thereof,


and kg_ - are the extinction coefficients for any soot present and the gas phases, respectively, of the suspension,
BB(Ts), BB(Ty_), BB(T_p), and BB( w) - are the black-body spectra appropriate to the temperature of any soot present, the gas, the particles, and the medium surrounding the suspension, respectively,
N - is the number density of the particles in the suspension,
A - is the geometric cross-sectional area of the particles,
L - is the effective path length through the gaseous suspension, and dl is the width of a theoretical slice at position 1 therealong,
<Z - is the spectral emmittance of the particles,
Q - is the ratio of the radiation scattering cross section to the geometric cross section of the particles, and

^ext ~ *-s tne ratio of the extinction cross section to the geometric cross section of the particles, and is equal to Q + Qaj-,g, Qabs bein<3 tne ratio of the absorption cross section to the geometric cross section of the particles, and wherein the foregoing quantities, other than N, A and L, are wavenumber dependent.
14. In apparatus for the analysis of a gaseous suspension of liquid particles, solid particles, or both, utilizing refracted components of radiation, the combination comprising:
(a) containment means having a sidewall defining a chamber for the flow of a gaseous suspension of particles along a path therethrough, at least one port being provided in said sidewall to provide optical access to said path;
(b) source means for providing
electromagnetic radiation directed inwardly from substantially all peripheral points about said path; and
(c) means for collecting radiation emanating from said containment means, said containment means, source means and collecting means being so adapted that components of radiation emanating from said source means that have been diverted from their original paths due to interaction with the particles of the suspension can be substantially discriminated from radiation that has not been so diverted.
15. The apparatus of Claim 14 additionally including second source means for providing an electromagnetic radiation beam, and second radiation colleσting means, said second source means and second collecting means being disposed in effective optical alignment with one another and being adapted to measure radiation transmitted by the particles of the suspension during passage through said containment means.
16. The apparatus of Claim 15 additionally including electronic data processing means for analyzing the radiation collected by said first and second collecting means.
17. The apparatus of Claim 16 comprising a Fourier-transform spectrometer.
18. The apparatus of Claim 16 comprising a Fourier-transform infrared spectrometer, wherein said data processing means thereof is programmed to compare the representative spectrum to preestablished spectra indicative of a parameter for which the gaseous suspension is being analyzed, so as to fit the representative spectrum thereto and thereby determine the parameter, by application of at least one of the

following basic equation, generalized formulae, and equations derived therefrom:

E +


NAQgBB(Tw)} exp(-y)]dl.

wherein "y" is the integral; J1 (k„ *+ k, NAQeχt)dl

E »
[kgBB (T ) +k BB (T ) +NA£BB (T ) +NAQgBB (T ) ]•
[l-exp(-(ks+kg+NAQeχt)L)]

ks + kg + NAζ**ext
and
(1-/) = l-exp[-(kg + kg + NAQeχt) ];
wherein:
E - represents any collected radiation emanating from the gaseous suspension and not transmitted therethrough,
/ - represents the ratio of any collected radiation that is transmitted through the suspension, divided by radiation that would be transmitted in the absence thereof,
ks and kg - are the extinction coefficients for any Λ soot present and the gas phase, respectively, of the suspension.

BB(Tg), BB(T ), BB(T ), and BB(Tw) - are the black-body spectra appropriate to the tempλsτature of any soot present, the gas, the particles, and the medium surrounding the suspension, respectively,
N - is the number density of the particles in the suspension,
A - is the geometric cross-sectional area of the particles,
L - is the effective path length through the gaseous suspension, and dl is the width of a theoretical slice at position 1 therealong,
fς - is the spectral emmittance of the particles,
Q - is the ratio of the radiation scattering cross section to the geometric cross section of the particles, and
Q . - is the ratio of the extinction cross section to the geometric cross section of said particles, and is equal to Qg + Qabs, Qabs being the ratio of the absorption cross section to the geometric cross section of the particles, and wherein the foregoing quantities, other than N, A and L, are wavenumber dependent.
19. The apparatus of Claim 15 wherein said sidewall of said containment means has a second optical access port therein aligned transversely with said one port on the opposite side of said flow path, said second source means and second collecting means being effectively disposed to opposite sides of said containment means and optically aligned with one another through said access ports.
20. The apparatus of Claim 14 wherein said sidewall of said containment means substantially surrounds said flow path and has an energy radiating surface thereon providing said first-mentioned source means, the configuration of said sidewall surface and the positions thereof and of said collecting means with respect to said access port substantially limiting the radiation from said surface impinging upon said collecting means to that which has been so diverted,, and thereby effectively providing the radiation discrimination capability of said apparatus.
21. The apparatus of Claim 20 wherein said radiating surface is of generally circular cross-sectional configuration in planes transverse to the flow path axis.
22. The apparatus of Claim 21 wherein said sidewall of said containment means has a second optical access port therein aligned transversely with said one port on the opposite side of said flow path, said second port providing a non-radiating area on said surface and thereby cooperating to provide the discrimination capability of said apparatus.
23. The apparatus of Claim 20 wherein said containment means includes means for heating said energy radiating surface.

24. The apparatus of Claim 23 having a sample compartment adapted for seating a cell, and additionally including a cell seated within said sample compartment and providing containment means for said apparatus.
25. The apparatus of Claim 15 additionally including means for coding the radiation from said second source means, said second collecting means being adapted to discriminate the coded radiation from other radiation which may impinge thereupon.
26. The apparatus of Claim 25 wherein said coding means comprises an interferometer effectively interposed in the path of radiation from said second source means to said containment means.
27. The apparatus of Claim 26 wherein said first-mentioned collecting means is disposed along said path of radiation, effectively between said second source means and said interferometer, and wherein said system additionally includes diverter means for establishing a radiation path between said containment means and either said second source means, said first collecting means, or both, whereby measurements of radiation transmitted through and/or emanating from said containment means can be made, respectively.
28. The apparatus of Claim 27 wherein said diverter means is operative to selectively either permit passage of radiation from said second source means to said containment means, or block such passage of radiation while simultaneously directing radiation from said containment means to said first collecting means.
29. The apparatus of Claim 27 wherein said diverter means is adapted to simultaneously permit passage of radiation from said second source means to said containment means while directing radiation therefrom to said first collecting means, said diverter means having a first portion which is transparent to the radiation from said second source means, and a second portion which is opaque thereto and is reflective of radiation from said containment means ' and directed theretoward, whereby such transmitted and emanating radiation can simultaneously be measured using said second and first collecting means, respectively.
30. The apparatus of Claim 24 wherein said cell has a generally cylindrical sidewall and end walls cooperatively defining said chamber thereof, said sidewall having a pair of access ports positioned diametrically thereon, and said end walls having means defining inlet and outlet channels therethrough, aligned substantially on the longitudinal axis of said cell, for the injection and removal of particles thereinto and therefrom, respectively, said inlet channel providing means for injecting the suspension, said cell, also having means by which the temperature of said inlet and outlet channel defining means can be controlled independently of said means for heating said radiating surface.

31. In a method for the analysis of at least one parameter of a gaseous suspension of liquid or solid particles, or both, the steps comprising:
a. providing a gaseous suspension of
particles;
b. causing electromagnetic radiation from at least one source to impinge upon said suspension;
c. collecting spectral radiation from said so irradiated suspension;
d. developing a spectrum representative of the intensity of the collected radiation as a function of wavenumber; and
e. comparing said representative spectrum to preestablished spectra indicative of the parameter for which said suspension is being analyzed, and fitting said representative spectrum thereto to determine said parameter, said comparison being made by application of the basic equation, or equations derived therefrom:

E -= fJ [{k BB(T ) + k BB(T ) + NA£BB( ) +
o 9 9
NAQsBB(Tw)} exp(-y)]dl.

wherein "y" is the integral: j (k + kg + NAQgχt)dl and wherein: -66- E - represents any collected radiation emanating from said gaseous suspension and not transmitted therethrough,
k and - are the extinction coefficients for any soot present and the gas phases, respectively, of the suspension,
BB(TS), BB(Tg), BB(Tp), and BB(Tw) - are the black-body spectra appropriate to the temperature of any soot present, the gas, the particles, and the medium surrounding said suspension, respectively,
N - is the number density of the particles in the suspension,
A - is the geometric cross-sectional area of said particles,
L - is the effective path length through the gaseous suspension, and dl is the width of a theoretical slice at position 1 therealong,
£ - is the spectral emmittance of the particles,
Q - is the ratio of the radiation scattering cross section to the geometric cross section of the particles, and
Q_„4 - is the ratio of the extinction cross section to the geometric cross section of said particles, and is equal to Qg + Qabs, Qabs being the ratio of the absorption cross section to the geometric cross section of the particles, and wherein the foregoing quantities, other than N, A and L, are wavenumber dependent.

32. The method of Claim 31 wherein said suspension provided is substantially homogeneous, and wherein said comparison is made by application of at least one of the generalized formulae:
E =
[kgBB(Ts) +kgBB(Tg) +NA£BB(Tp) + AQsBB (Tw) ] •
[1-exp (- (kg+kg+NAQeχt) ) ]
kβ +k„ + NAQext
and
(1- ) = l-exp[-(k NAQeχt)L],
+ kg +
wherein ' " represents the ratio of any collected radiation that is transmitted through the suspension, divided by radiation that would be transmitted in the absence thereof,
33. The method of Claim 32 including the step of passing said gaseous suspension to be analyzed through a chamber, having at least one port for optical access thereinto, at a flow rate of about 1 to 100 meters per second, said step "b" being effected during passage of said suspension through said chamber.
34. The method of Claim 33 including the additional step of passing a stream of gas into said chamber simultaneously with and as a sheath about said particle suspension.
35. The method of Claim 33 wherein said electromagnetic radiation is a beam brought to a focal volume within said chamber, and wherein said suspension of particles is passed substantially through said focal volume .
36. The method of Claim 35 wherein said particles in said suspension are in the form of a monodispersed stream.
37. The method of Claim 31 wherein electromagnetic radiation of infrared wavelengths is utilized for irradiating said suspension.
38. The method of Claim 32 wherein electromagnetic radiation of infrared wavelengths is utilized for irradiating said suspension, and wherein said step of analyzing said radiation comprises Fourier-transform spectroscopic measurement thereof.
39. In a method for the analysis of at least one parameter of a gaseous suspension of liquid or solid particles, or both, the steps comprising:
a. causing a beam of electromagnetic
radiation to impinge upon the suspension to be analyzed;
b. collecting radiation transmitted through and emanating from said so irradiated suspension;
c. distinguishing said transmitted radiation from said emanating radiation;
d. developing spectra representative of the intensity of the transmitted and emanating
radiation collected and distinguished in said steps b. and c, as functions of wavenumber; and e. comparing said representative spectra to preestablished spectra indicative of a parameter for which said suspension is being analyzed, and fitting said representative spectra thereto to determine said parameter.
40. The method of Claim 39 including the additional step of providing said suspension as a substantially homogeneous volume, and wherein said comparison is made by application of the generalized formulas:

E =
[ gBB(Ts)+k BB(T )+NA^BB(T )+NAQgBB(Tw)].
'[l-exp(-(kg+kg+NAQeχt)L)]

ks + NAQext
and
(1-/) = l-exp[-(kg + kg + NAQeχt)L];
wherein:

E - represents any collected radiation emanating from said gaseous suspension and not transmitted therethrough,
Υ - represents the ratio of any collected radiation that is transmitted through the suspension, divided by radiation that would be transmitted in the absence thereof,
ks and kg - are the extinction coefficients for any soot present and the gas phases, respectively, of the suspension.

BB(Tg), BB(Tg), BB(Tp), and BB(Tw) - are the black-body spectra appropriate to the temperature of any soot present, the gas, the particles, and the medium surrounding said suspension, respectively,
N - is the number density of the particles in the suspension,
A - is the geometric cross-sectional area of said particles,
L - is the effective path length through the gaseous suspension,
- is the spectral emmittance of the particles,
Q - is the ratio of the radiation scattering cross section to the geometric cross section of the particles, and
Q . - is the ratio of the extinction cross section to the geometric cross section of said particles, and is equal to Qg + Qabs - Qabs being the ratio of the absorption cross section to the geometric cross section of the particles, and wherein the foregoing quantities, other than N, A and L, are wavenumber dependent.
41. The method of Claim 40 wherein the temperature "T " of the medium surrounding said suspension is known and said parameter for analysis is particle temperature "T " , said representative spectrum being that of
IT
normalized emission "E " , wherein E = E/(l-7") •
42. The method of Claim 41 wherein said step "a" is carried out under conditions at which Qext has a value of 1, at frequencies at which there is no absorption of radiation by soot or the gas phase, or such absorption can be ignored, and with said gaseous suspension to be analyzed contained in a chamber having at least one port for optical access thereinto, said surrounding medium being the wall surface defining said chamber and said comparison being made based upon the equation:
En = £l3B(Tp) + (ι_£) BB(Tw).
43. The method of Claim 40 wherein the temperature "T " of said particles and the temperature "T " of the medium surrounding said suspension are known, and said parameter for analysis is emittance " ", said representative spectrum being that of normalized emission "E ", wherein En = E/(l-7) .
44. The method of Claim 43 wherein said particle temperature "T " is substantially higher than said surrounding medium wall surface temperature "T ", said comparison being made based upon the equation:
£ = En /BB(Tp).
45. The method of Claim 43 wherein said surrounding medium comprises the surface of a wall defining a chamber in which said suspension is contained when said step "a" is carried out, and wherein the temperature

"Tw" of said wall surface is substantially higher than said particle temperature "T " , said comparison being made based upon the equation:
£= 1 - [En /BB(TW)].
46. The method of Claim 45 including the further step of estimating the wavenumber-dependent linear absorbtion coefficient characteristic "ky " of said composition, said estimation being carried out by measuring the value of E ; determining a value for the average transmission nτ"" for the inside of the particles of said suspension by application of the equation:
- = En /BB(Tw);
characterizing the gross geometry of the particles of said suspension in terms of a characterizing dimension "D"; selecting, based upon said characterization of geometry, a suitable preestablished curve expressing (-In T') as a function of k # D; and estimating the value of k from said selected curve.
47. In a method for the quantitative compositional analysis of a gaseous suspension of liquid or solid particles, or both, the steps comprising:
a. passing a gaseous suspension of particles to be analyzed into a chamber having at least one port for optical access thereinto;
b. causing electromagnetic radiation from at least one source to impinge at off-axis angles upon the particles of said suspension during passage through said chamber, said off-axis angles
consisting essentially of angles oblique to said one access port;
c. collecting through said one port radiation from . said so irradiated particles, said collected radiation being limited, by virtue of said off-axis impingement, substantially to rays from said source refracted or otherwise diverted by said particles;
d. developing a spectrum representative of the path and amplitude of said collected radiation as a function of wavenumber; and
e. comparing said representative spectrum to preestablished spectra indicative of the
compositional parameter for which said suspension is being analyzed, and fitting said representative spectrum thereto to determine said parameter.
48. The method of Claim 47 wherein said cavity is defined by a wall substantially surrounding said gaseous suspension, and wherein the surface of said wall is maintained at a temperature substantially higher than the temperature of said particles and provides said one radiation source.
49. The method of Claim 48 wherein said suspension is passed through said chamber at a flow rate sufficiently high to avoid substantial heating of said particles by the radiant energy emanating from said wall surface.
50. The method of Claim 49 wherein said wall surface is at a temperature about 500 Centigrade degrees or more above the temperature of said particles.
51. The method of Claim 50 wherein, prior to entry into said cavity, said suspension is maintained at a temperature suitable to ensure that said particles thereof will be substantially at room temperature therein.
52. The method of Claim 48 wherein said wall surface is of substantially circular cross-section in planes perpendicular to the flow axis of said suspension, and wherein said diverted radiation is collected at a location diametrically disposed with respect to a second optical access port in said wall surface, said second port being on-axis and constituting a non-radiating area of said wall surface, thereby so limiting said collected radiation.
53. The method of Claim 48 wherein a beam of electromagnetic radiation from a second source is caused to impinge upon said particles, said collecting step being carried out by collecting and discriminating said diverted rays from components of said radiation beam transmitted through said particles, said representative spectrum being that of normalized emission "E " , wherein


54. The method of Claim 53 wherein said suspension is substantially homogeneous, and wherein said

comparison is made by application of the following generalized formulae:

E =
[kgBB(Tg)+kgBB(Tg)+NA£BB(Tp)+NAQgBB(Tw)]*
[1-exp (- (ks+kg+NAQeχt) L) ]

ks + kg. + NAQext
and
(1-7) *-* l-exp[-(kg + kg + NAQeχfc)L],
wherein:
E - represents any collected radiation emanating from said gaseous suspension and not transmitted therethrough,
j - represents the ratio of any collected radiation that is transmitted through the suspension, divided by radiation that would be transmitted in the absence thereof,
ks„ and kg„ - are the extinction coefficients for any-* soot present and the gas phases, respectively, of the suspension,
BB(τ S), BB( y), BB(T_), and BB(TW) - are the black-body spectra appropriate to the temperature of any soot present, the gas, the particles, and the medium surrounding said suspension, respectively,
N - is the number density of the particles in the suspension,
A - is the geometric cross-sectional area of said particles.

L - is the effective path length through the gaseous suspension,
- is the spectral emmittance of the particles,
Q - is the ratio of the radiation scattering cross section to the geometric cross section of the particles, and
Q . - is the ratio of the extinction cross section to the geometric cross section of said particles, and is equal to Qg + Qabsf ■__>_ being the ratio of the absorption cross section to the geometric cross section of the particles, and wherein the foregoing quantities, other than N, A and L, are wavenumber dependent.
55. The method of Claim 54 wherein said transmitted radiation components and said diverted irays are collected sequentially with said suspension flowing at a constant rate through said cavity.
56. The method of Claim 54 wherein said transmitted radiation components and said diverted rays are collected simultaneously.
57. The method of Claim 54 including the further step of estimating the wavenumber-dependent linear absorbtion coefficient characteristic "k/ " of said composition, said estimation being carried out by measuring the value of E ; determining a value for the average transmission "T**" for the inside of the particles of said suspension by application of the equation:
T* = En /BB(Tw);
characterizing the gross geometry of the particles of said suspension in terms of a characterizing dimension "D"; selecting, based upon said characterization of geometry, a suitable preestablished curve expressing (-In ') as a function of k^ D; and estimating the value of k, from said selected curve.
58. In a method for the analysis of particle size in a -gaseous suspension of liquid or solid particles, or both, the steps comprising:
a. providing a substantially homogeneous gaseous suspension of particles;
b. causing a beam of electromagnetic radiation to impinge upon said suspension;
c. selectively collecting radiation
transmitted through said so irradiated suspension;
d. developing a spectrum representative of the intensity of the collected radiation as a function of wavenumber; and
e. comparing said representative spectrum to preestablished spectra indicative of particle size, and fitting said representative spectrum thereto to determine a particle size parameter, said representative spectrum being that of (1-7^) and said comparison being made based upon the formula:
(1-7) = l-exp[-(k<5 + k + NAQeχt)L]
wherein:
ks and kg - are the extinction coefficients for any soot present and the gas phase, respectively, of said suspension,
N - is the number density of said particles in said suspension,
A - is the geometric cross-sectional area of said particles,
L - is the effective path length through said gaseous suspension, and
Q . - is the ratio of the extinction cross section to the geometric cross section of said particles, and is equal to Q " + Qabs»- Qat,s being the ratio of the absorption cross section to the geometric cross section of said particles, and Q 5 being the ratio of the radiation scattering cross section to the geometric cross section of said particles, the quantities other than N, A and L being wavenumber dependent.
59. The method of Claim 58 wherein said step "b" is carried out with said gaseous suspension to be analyzed contained in a chamber having a pair of aligned ports for optical access thereinto, and wherein the aperture size of the one of said ports lying beyond the zone of interaction of said beam with said particles, relative