RESUMO
Three-dimensional (3D) shape reconstructions and metrology measurements are often limited by depth-of-field constraints. Current focus-detection-based techniques are insufficient to profile out-of-focus 3D objects with high axial accuracy. Extended-focus imaging (EFI) techniques can improve the range and precision of such measurements. By incorporating digital refocusing with multiwavelength interferometry, a holographic imaging solution is presented in this paper to accurately measure 3D objects over a large depth range. Accuracy and repeatability of the proposed EFI technique are validated by digital simulations and refocusing experiments. A reconstruction example demonstrates the feasibility of high-precision 3D measurements of objects deeper than the system's classical depth of field.
RESUMO
A line scan interferometer, which comprises a visible supercontinuum source coupled to Fourier domain Michelson interferometer, is used to obtain 3D images of ~300 µm high solder balls on a semiconductor die with 125 nm axial and 15 µm lateral resolution. The ability to measure curved surfaces enables the determination of solder ball shape defects in addition to ball height. We show that the maximum measurable angular tilt from the sample surface normal for a given source power depends on the surface roughness of the sample. As an example, we demonstrate height measurement over +/-20 degrees from the normal on the solder balls and over +/-60 degrees on a rough steel ball bearing sample.
RESUMO
Supercontinuum (SC) light with a continuous spectrum covering 0.45-1.2 microm is scaled from 250-740 mW by varying the repetition rate of an amplified, frequency doubled, telecom laser diode. Efficient SC generation requires minimal non-linearity in the amplifier and anomalous dispersion pumping close to the fiber zero dispersion wavelength. Based on simulations, we present a 2-stage design that separates pulse break-up from spectral broadening to enhance the SC bandwidth for quasi-CW pumping.
