The stereolithography (SL) process has benefited from many advances in the last four to five years. These include new resins with reduced shrinkage and curl distortion, enhanced software, and improved scanning techniques. One can produce highly accurate parts for most dimensions with a few mils of the design value as shown in numerous accuracy and benchmarking studies. SLA systems use a laser beam focused to a spot size of 200-250 micrometers . This limits the range of applications where SL can provide accurate models to parts which do not contain very small features i.e. wall thickness values less than about 300 micrometers . Industries that manufacture products involving components with small features include electronics and medical. In this presentation we describe an extension of the SL technology to applications involving small features. This capability is achieved by reducing the laser focal spot size in an SLA-250 to 75 micrometers . The technological principle behind the spot size reduction is described in the representation, together with process issues and applications of the technology.
Stereolithography is a Rapid Prototyping and Manufacturing (RP&M) technique which can be used to produce 3D plastic parts directly out computer files generated by CAD. Stereolithography systems use ultraviolet lasers to solidify liquid resin into the desired form as defined by the CAD file. Solidified plastic parts are built completely automatically (i.e. unattended) a layer at the time (typical laser thickness is 150 micrometers ) on the surface of the liquid resin. A slice cross section of the part is solidified by directing the laser beam onto the photopolymer surface using two (x and y direction) high speed vector scanning mirrors. This talk describes recent advances involving laser and optics technology applied to stereolithography and RP&M. These include: (1) improved reliability and power from ultraviolet gas lasers (HeCd and Argon Ion), (2) laser beam conditioning control to achieve accurate realization of small features, (3) advanced use of a fast AOM (acousto-optic modulator) shutter in the beam steering, and (4) improved performance of fast scanning mirrors. The application of emerging all solid state ultraviolet laser sources for stereolithography will also be discussed.
We measure the magnitude and phase of the degenerate third-order nonlinear optical susceptibility (chi) (3)llll of solutions of various bis-thienyl polyenes (n-BTP) with the number n of the conjugated double bonds ranging from 3 to 9. We study both neutral and bipolaronic (i.e., doubly ionized) forms of n-BTP. We find that, within experimental error, (chi) (3)llll is proportional to nb where b-5.5 at 532 nm for our neutral n-BTP samples which have 3 <EQ n <EQ 9, and b-14 at 1.06 micrometers for the bipolaron state samples which have 6 <EQ n <EQ 9 where the probing laser wavelength is close to an absorption band. We calculate (chi) (3)llll of the bipolaronic n-BTP assuming it is associated with this absorption band acting as a two-level system and find good agreement with experiment.
We use a pump-probe technique to measure the change in optical transmission through a 1 cm C60/benzene (0.58 g/l) solution caused by a 532 nm 25 ps `pump' pulse having fluence up to approximately 10 mJ/cm2. Temporal dependence indicates that transmission drops within the pump pulse width and stays at the reduced level up to our maximum delay time (approximately 10 ns). If we use the standard three-level model for the C60 molecule we deduce that either the excited-singlet-to-triplet crossing happens faster than our pulse width or the two states have indistinguishable absorption cross-sections ((sigma) S approximately equals (sigma) T) at our laser wavelength. We believe that the latter assumption is more probable, and interpret our data by a simple two-cross-section ((sigma) O, (sigma) T) model. We find that the difference (sigma) T - (sigma) O is (3.5 +/- 0.2) X 10-17 cm2. We measure the ground state absorption cross-section (sigma) O to be (3.5 +/- 0.3) X 10-18 cm2 in an independent experiment.