One dimensional beam homogenization with a single aspheric lens for accurate particle sizing instrumentation
Beam homogenization with a single aspheric lens that converts the divergent Gaussian intensity profile of a laser diode beam to a convergent beam with a one-dimension flat top profile, which enhances the accuracy of a particle sizing instrument by delivering a uniform amount of energy across an aerosol microfluidic channel.
1. A light source for illuminating an aerosol flow containing particulate matter for analysis, comprising:
a laser diode;
a bi-convex singlet aspheric lens;
said aspheric lens having an objective side aspheric profile satisfying the equation:
Z
(
r
)
=
r
3
/
R
1
+
1
-
(
1
-
K
)
(
r
2
/
R
2
)
+
A
2
·
r
2
+
A
4
·
r
2
+
A
6
·
r
2
+
A
8
·
r
2
;
and
an image side aspheric profile satisfying the equation:
Z
(
r
)
=
r
3
/
R
1
+
1
-
(
1
-
K
)
(
r
2
/
R
2
)
+
A
2
·
r
2
+
A
4
·
r
2
+
A
6
·
r
2
+
A
·
r
2
8
+
A
10
·
r
2
+
A
12
·
r
2
;
where A represents the 2 nd , 4 th , 6 th , 8 th , 10 th and 12 th order aspheric coefficients respectively; and where R denotes the radius of the curvature of the vertex of the aspheric lens surface; and K denotes the conic constant; and
an aerosol flow at a working distance from said laser diode emitting point;
wherein the ray trajectory of a divergent Gaussian light beam from said laser diode is modified to a convergent flat top profile light beam in the fast axis direction at said aerosol flow.
2. The singlet aspheric lens of claim 1 where the variables of the expression for said objective aspheric surface are:
R=8
K=3.9
A2=−4.9e−5
A4=1.6e−03
A6=5.2e−04
A8=−4.7e−04.
3. The singlet aspheric lens of claim 1 where the variables of the expression for said image aspheric surface are:
R=−2.7
K+−3.85e−02
A2=1.39e−03
A4=2.27e−03
A6=3.77e−03
A8=1.15e−04
A10=2.45e−05
A12=3.12e−06.
4. The singlet aspheric lens of claim 1 where the said working distance is 24 mm from the laser diode emitting point.
5. The singlet aspheric lens of claim 1 wherein said lens is constructed of K-PBK40 material.
6. The light source of claim 1 , including:
a rectangular aperture placed between said aspheric lens and said aerosol flow,
whereby said aperture truncates the smooth edges of said flat top beam and controls said beam size at said aerosol flow.