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CCD CALIBRATION WITH UV LAMP

IP.com Disclosure Number: IPCOM000010314D
Publication Date: 2002-Nov-20
Document File: 6 page(s) / 103K

Publishing Venue

The IP.com Prior Art Database

Abstract

CCD cameras are used for scientific studies and industrial applications where images with high resolution and sensitivity are required. For UV applications, the CCD pixel response is normally low in the UV range due to low quantum efficiency. By applying a UV enhanced layer on the CCD chip, the quantum efficiency for UV can be increased substantially. A calibration tool has been designed where variations in pixel response due to non-uniformities in the UV enhanced layer are corrected with an accuracy of <0.5%. This has been achieved by using a uniform light source using an Hg lamp, resulting in local uniformity variations below 0.5%.

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CCD CALIBRATION WITH UV LAMP

Problem or object to be solved

CCD cameras are used for scientific studies and industrial applications where images with high resolution and sensitivity are required. For UV applications, the CCD pixel response is normally low in the UV range due to low quantum efficiency. By applying a UV enhanced layer on the CCD chip, the quantum efficiency for UV can be increased substantially.

A calibration tool has been designed where variations in pixel response due to non-uniformities in the UV enhanced layer are corrected with an accuracy of <0.5%. This has been achieved by using a uniform light source using an Hg lamp, resulting in local uniformity variations below 0.5%.

State of the art

Calibration of CCD cameras is performed as a standard routine for imaging applications. For calibration of the photo response non-uniformities, a procedure called flat-fielding is normally used. During this procedure, pixel-to-pixel response variations are corrected for by making gain and offset adjustments on each pixel. In our procedure, pixel-to-pixel as well as low frequency variations over the CCD chip caused by the non-uniformity of the UV enhanced layer are calibrated.

Disadvantage(s) of the state of the art

In standard flat-fielding calibration, the non-uniformity of the light source is not required to be known within high accuracy since variations between the gain in the CCD pixels are related to the CCD frame average. This will take care of high frequency variations resulting from pixel-to-pixel non-uniformities. However, if there are low frequency variations on the CCD chip, the intrinsic limitation on the calibration output is the uniformity of the light source. Therefore, the non-uniformity in the illumination from the calibration light source needs to be known for calibration of large-scale spatial variations over the CCD chip.

Short description of the idea

The set-up, which has been used for CCD calibration is described in figure 1 and figure 2 illustrating two different embodiments.

Fig1. A first embodiment of a calibration set-up for a CCD.

Fig. 2 A second´┐Ż embodiment of a calibration set-up for a CCD.

The calibration set-up according to the first embodiment consists of the following components:

1.        Hg lamp.

2.        Lamp house.

3.        Lamp shutter.

4.        Ozone filtering system or N2 purge line connected to the lamp house.

5.        An interference filter placed at the entrance port of the camera house.

6.        Two baffles placed on an optics rail, between the entrance port of the camera house and the CCD camera.

7.        An adjustable rectangular aperture placed in front of the camera opening.

8.        A CCD camera mounted on an XY translation stage.

9.        A camera house covering the optics rail and the CCD camera.

1). The Hg lamp emits photons with well-defined peaks ranging from UV to the visible spectrum. There is a peak at 253.7 nm, which has been used, in the present case. The Hg lamp is driven by a DC power supply for optimum stability and the output fro...