1. Spot-Projector System for the Measurement of Intra-Pixel Response
Young Sam YU
Background
Pixels on imaging sensors do not have uniform response across pixel area
Known intra-pixel sensitivity is important for high photometric precision analysis
Goals
Build a spot projector capable of producing a spot much smaller than the size of a pixel
Validate the spot projector’s capability
Measure the intra-pixel response for a HyViSI hybrid CMOS detector
Expected Spot Size
Diffraction limit = 1.22 λ f/D= 1.22 λ f/# = 0.61 λ/N.A. = 2.78 μm
Demagnification = 10X
Spot Size = sqrt( (Dia.diffraction limit)2 + (Demagnification of Image)2)
5.7 μm
1 μm
10 μm
1 mm
10 mm
(Incl. Diffraction)
(no. Diffraction)
Pinhole size
Spot-projector
Light guide
Neutral filter
Diffuser
Pinhole
Extension Tube
Linear Stages
Micro-objective lens
Infinitube lens
CCD
Figure 1. Top: Schematic diagram of optical Components
in Spot-projector with Ray Tracing (Red). Bottom: Setup
of Spot-Projector systems.
Result
Figure 2. Image of 10 mm pinhole with 10X demagnification. Blue lines represent the radius of the image. Left: Imaging of 10 mm pinhole. Right: Plot of intensity profile from selected radius (Blue region). Red line is at FWHM (59.5 pixels, 9 μm/pix). FWHM is 119 pixels and corresponds 1 mm image size. It is good match to the expected spot size.
Summary
Demonstrated that our Spot-projector is successfully working (Fig. 2) as expected .
Future Work
Measure the point spread function of the Spot-Projector using the Knife-edge technique.
Measure the Intra-Pixel Response of a HyViSI Hybrid CMOS image sensor.
This system will also be used to test the guiding detectors for the Large Synoptic Survey Telescope (LSST).
Spot-projector properties
Able to produce a spot as small as 5.7 µm to as large as 1 mm.
Mounted on a three axis stage giving it the capability to run automated scan sequences across many pixels.
Connected to a monochromator allowing us to control the wavelength of light.