Spot-Projector System for the Measurement of Intra-Pixel ResponseYoung 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

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).

Expected Spot Size

Diffraction limit = 1.22 λ f/D= 1.22 λ f/# = 0.61 λ/N.A. = 2.78 μm Demagnification = 10XSpot Size = sqrt( (Dia.diffraction limit)2 + (Demagnification of Image)2)

5.7 μm1 μm10 μm

1 mm1 mm10 mm

Expected Spot Size

(Incl. Diffraction)

Expected Spot Size

(no. Diffraction)

Pinhole size

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.

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.

Spot-projector

Light guide

Neutral filter

Diffuser

Pinhole

Extension Tube

Linear Stages

Micro-objective lens

Infinitube lensCCD

Figure 1. Top: Schematic diagram of optical Components in Spot-projector with Ray Tracing (Red). Bottom: Setup of Spot-Projector systems.