Ultrafast laser fabrication method and system
A laser fabrication method and a laser fabrication system. The laser fabrication system includes an ultrafast laser source configured to output a laser beam; and a digital micromirror device (DMD), configured to receive, shape, and scan the laser beam, wherein more than one binary holograms are synthesized to form a scanning hologram applied to the DMD. The shaped laser beam, containing one or multiple focal points, leaving the DMD, are focused to the sample for fast laser fabrication.
1. A laser fabrication system, comprising:
a laser source configured to output a laser beam;
a digital micromirror device (DMD), configured to receive and shape the laser beam with a scanning binary hologram, wherein the DMD functions as a programmable binary mask coded with the scanning binary hologram, and more than one binary hologram is synthesized to form the scanning binary hologram applied to the DMD; wherein the shaped laser beam leaving the DMD is focused to photoresists for parallel fabrication with a single or multiple shaped laser points; and
a spatial filter, configured to select a non-zero order beam diffracted from the scanning binary hologram, wherein the non-zero order beam is a −1st or +1st order beam, wherein the selected non-zero order beam is focused to the photo-sensitive resins.
2. The laser fabrication system according to claim 1 , wherein the DMD introduces negative angular dispersion to the laser beam; and the system further comprises a dispersion compensation unit, configured to transfer the laser beam from the laser source to the DMD with a positive angular dispersion for neutralizing the negative angular dispersion.
3. The laser fabrication system according to claim 2 , wherein the dispersion compensation unit includes a blazed transmission grating and a mirror.
4. The laser fabrication system according to claim 1 , wherein wavefront information for wavefront correction is further included in the scanning binary hologram.
5. The laser fabrication system according to claim 1 , wherein the laser beam from the laser source is expanded to match an aperture of the DMD.
6. The laser fabrication system according to claim 1 , further comprising an objective lens via a set of relay optics configured to focus the shaped laser beam.
7. The laser fabrication system according to claim 6 , wherein the set of relay optics is a 4-f system consisting of two lenses.
8. The laser fabrication system according to claim 6 , wherein the spatial filter is placed at a back focal plane of the set of relay optics to spatially select a non-zero order beam diffracted from the scanning binary hologram.
9. The laser fabrication system according to claim 1 , further comprising a microscopic imaging system configured to monitor fabrication processes performed by the shaped laser beams.
10. The laser fabrication system according to claim 1 , further comprising a position stage configured to mount and maneuver samples to a location where the sample will be laser processed.
11. The laser fabrication system according to claim 1 , wherein the system further comprises a lens pair comprising a first lens L 1 and a second lens L 2 , configured to collimate and expand the laser beam and image the beam onto the DMD, wherein the first lens L 1 has a focal length f L1 and the second lens L 2 has a focal length f L2 , wherein a ratio of f L1 to f L2 is equal to a ratio of cone angles Δθ G and Δθ D , the ratio of cone angles Δθ G and Δθ D satisfying the following equation set:
Δθ
G
Δ
θ
D
=
m
G
d
D
cos
θ
iD
m
D
d
G
cos
θ
mG
,
wherein m is an integer indicating a diffraction order, d is a grating period, θ i and θ m are incident and diffraction angles of a m th order diffraction, respectively, and G and D are the grating and the DMD, respectively.
12. The laser fabrication system according to claim 1 , wherein a plurality of binary holograms is superposed to form a target hologram of a target wavefront with a plurality of focal points, and the target hologram is used as the scanning hologram applied to the DMD.
13. The laser fabrication system according to claim 12 , wherein the plurality of binary holograms is superimposed based on an equation:
h
(
i
,
j
)
=
{
1
,
-
A
(
x
,
y
)
≤
∑
k
=
1
n
B
k
sin
(
2
π
B
k
(
x
,
y
)
T
k
+
φ
k
(
x
,
y
)
)
≤
A
(
x
,
y
)
0
,
otherwise
wherein A(x,y)·exp [iφ(x,y)] is the target wavefront including k focal points, A(x,y)∈L[0,1] and φ(x,y) represent an amplitude and a phase of an electric field, x and y are coordinates in Cartesian coordinate system;
wherein h(i, j) represents a binary value of micromirrors on the DMD at (i, j), and B k , R k (x,y), T k and ϕ k are relative amplitude factor, tilted phase, grating period, and phase for the k th focal point respectively.
14. A method for laser fabrication, comprising:
outputting a laser beam from a laser source;
shaping the laser beam with a scanning binary hologram by a digital micromirror device (DMD) functioning as a programmable binary mask coded with the scanning binary hologram synthesized from more than one binary hologram;
focusing the shaped laser beam to photo-sensitive resins for parallel fabrication with a single or multiple shaped laser points; and
spatially selecting a non-zero order beam diffracted from the scanning binary hologram, wherein the non-zero order beam is −1st or +1st order beam, wherein the selected non-zero order beam is focused to the photo-sensitive resins.
15. The method according to claim 14 , further comprising neutralizing an angular dispersion introduced by the DMD to the laser beam.
16. The method according to claim 14 , wherein the scanning binary comprises wavefront modulating information for wavefront correction.