This paper studied manufacturing resolutions of micro structures made by two photon polymerization (TPP) technology with different manufacturing parameters. The light source used for the TPP manufacturing system was a low-cost 532 nm Nd:YAG green laser, and the material used was commercial resin Photomer 3015. Two objective lenses, one with magnification of 100 times (100x) and numerical aperture (NA) of 1.3 and the other with 50x and NA0.8 were used in TPP production. The manufacturing resolution, which is also named as voxel size, changed with different manufacturing parameters such as laser power and exposure time. The measurement results of TPP structures manufactured with different manufacturing parameters indicated that the minimum line width produced by the 100x-NA1.3 lens could be reduced down to 67 nanometer (nm), which was quite good for TPP systems with low-cost Nd:YAG laser.
We review our recent results towards the development of a turnkey 3D laser printer, based on self-Q-switched microchip Nd:YAG lasers, with reproducible sub-100nm resolution, and with large-scale (cm) and fast-speed (cm/sec) capability at micron resolution. First of all, we report on line fabrication with 70nm lateral, and 150nm longitudinal resolutions without significant shrinking. This is due to the tight focusing with green visible wavelength, large numerical aperture, and excellent resin properties. Secondly, we report on two-photon sensitive photoacid generators that lead to efficient 3D microfabrication with epoxy SU-8 resin. Thirdly, we demonstrate high-speed microfabrication of large scale, millimeter size, scaffolds and cemtimeter height needle with high repetition rate (130Khz), and high average power (1W) amplified microchip laser. Finally we demonstrate the two-photon induced cross-linking of antibodies to determine the type of red blood cells in microfluidic channels.
This paper studies the quality of lines and surfaces fabricated by the two-photon polymerization (TPP) technology.
Micro lines and surfaces fabricated by TPP are accumulation of micro spots, and their external shapes can be simulated
and predicted from manufacturing parameters, such as laser power, exposure time, scanning speed, spot gap, and line gap.
The correctness of predicted shapes is verified by measuring product shapes by SEM and AFM. The purpose of this
study is to find the best parameters for increasing line smoothness and reducing surface roughness. Firstly, the total
energy absorbed in each point within the work piece space is simulated by adding up all the laser spots of the scanning
path. The point with absorbed exposure energy exceeding the resin threshold energy forms a polymerized spot of the
product, and the product shape can be obtained. Secondly, micro lines and surfaces with different manufacturing
parameters are fabricated and product shapes are measured by both SEM and AFM. The simulated shape and the
measured shape of the product with specific manufacturing parameters are compared. Shapes from simulation and
fabrication have the same trend. Results of this study can be applied in manufacturing TPP products with complex shapes
for better surface quality.
3D shape measurement based on structured light system is a field of ongoing research for the past two decades. For 3D
shape measurement using commercial projector and digital camera, the nonlinear gamma of the projector and the
nonlinear response of the camera cause the captured fringes having both intensity and phase errors, and result in large
measurement shape error. This paper presents a simple intensity error correction process for the phase-shifting method.
First, a white flat board is projected with sinusoidal fringe patterns, and the intensity data is extracted from the captured
image. The intensity data is fitted to an ideal sine curve. The difference between the captured curve and the fitted sine
curve are used to establish an intensity look-up table (LUT). The LUT is then used to calibrate the intensities of
measured object images for establishing 3D object shapes. Research results show that the measurement quality of the 3D
shapes is significantly improved.
We review our recent advances in two-photon induced photochemistry to fabricate three-dimensional micro-objects
made in polymers, proteins and noble metals using Q-switched Nd:YAG microchip lasers. We have synthesized a new
photoinitiator that is about 4 times more sensitive for two-photon polymerisation with sub-nanosecond pulses at 532 nm.
We describe the improvement of our fabrication process and strategies to obtain solid microstructures that correspond to
their models. We report on our progress to make silver microstructures by the photoreduction of silver nitrate with
microchip lasers at 1064nm.
We study the rotation of photo-driven Archimedes screw with multiple blades. The micron-sized Archimedes screws are
readily made by the two-photon polymerization technique. Free-floating screws that are trapped by optical tweezers
align in the laser irradiation direction, and rotate spontaneously. In this study we demonstrate that the rotation speeds of
two-blade-screws is twice the rotation speed of one-blade-screw. However, more complex 3-blade-screws rotate slower
than 2-blade-screws due to their limited geometry resolution at this micron scale.
This paper presents an approach to reconstruct solid models from triangular meshes of STL files. First, suitable slicing
planes should be selected for extracting parallel intersection contours, which will be used for solid model reconstruction.
Usually, a suitable flat region of triangular meshes of the STL model is selected as the bottom surface, and it can be fitted
into a plane from the selected flat region. The flat region is separated by a mesh segmentation method, which uses a
specified small threshold dihedral angle to divide all triangular facets into separated regions. Next, a series of parallel
slicing contours are obtained by cutting the STL model through specified parallel cutting planes. Slicing contours are
originally composed of a lot of line segments, which should be simplified and refitted into 2D NURBS curves for data
reduction and contour smoothing. The number of points on each slicing contour is reduced by comparing the variation of
included angles of each two adjacent line segments. Reduced points of each slicing contour are fitted into a NURBS
curve in commercial CAD software. Finally, with a series of parallel 2D NURBS curves, the solid model of the STL
facets is established by loft operations supplied in almost all popular CAD software. The established solid model can be
used for other post processing such as finite element mesh generation.
This paper proposes a new multiple three-step color phase-shifting method for measuring 3D shape of objects. Firstly,
multiple color fringe patterns are designed and projected onto the object surface by a projector. Distorted fringe patterns
on the object surface are captured by a digital camera, and intensities of each pixel in the red, green and blue channels are
obtained from the captured color images. Phase values of all pixels are calculated by the phase-shifting method from the
obtained RGB intensities. Then, the phase-unwrapping technique is applied to convert phase values to the height of the
object surface. Finally, an integrated program is developed by combining phase-shifting process and phase-unwrapping
process. With the developed program, several measurement examples are investigated. From the measurement result, it
shows that better 3D shape results can be obtained from the proposed method.