Evaluation of the functional performance of visible imaging devices requires
spatially uniform illumination. Commercially available test illumination sources
currently on the market have a small area of illumination and non-uniformity
that is greater than 3%.
The production of uniform illumination (irradiance) of high intensity has
always been a challenge. Existing illumination sources capable of providing
spatial non-uniformity approaching 1% are traditionally based on an integrating
sphere to produce the randomization of the energy distribution. Typically the
integrating sphere is large and bulky. Pulse instruments has taken advantage of
the properties of the integrating sphere but in a significantly smaller package.
An optical system is added to the integrating sphere that preserves the
uniformity and increases the area of illumination.
The PI-4875 Precision Illumination Source developed by Pulse Instruments
provides a spatially uniform distribution of irradiance over a large area. The
large, uniform illumination area allows the testing of the larger devices, such
as linear devices, without compromising the testing process. In addition this
large area of illumination can be used to illuminate several smaller devices
simultaneously for parallel testing.
Specific spectral bandpass and irradiance levels are selectable through
computer control. Narrow band interference filters determine specific spectral
pass bands. These filters can have values throughout the illuminator spectral
range of 400 nm to 1000 nm. A set of Inconel neutral density filters and the
iris determine the irradiance level. The unit is low maintenance and can be
mounted in any position to accommodate prober and part handler environments.
The design is based on the use of a small integrating sphere. The neutral
density and spectral bandpass filters process the output energy from the
integrating sphere before being delivered to the optical system. A closed-loop
monitoring system maintains the luminance stability to
±0.1% over a short
period and less than ±1% over a long period. Located in the optical lens
system is an iris type aperture. This iris is controllable from fully open to
fully closed via the computer in 650 steps.
One filter wheel holds up to 6 selectable bandpass filters that can be
selected within the range of 400 nanometers to 1,000 nanometers. The second
filter wheel holds up to 6 selectable neutral density filters. Using the iris
and the neutral density filters together to control the output will provide a
wide range of luminance. The user can incorporate a much wider selection of
bandpass filters and/or neutral density filters with additional filter wheels.
The PI-4875 incorporates a unique design that simplifies the changing of both
the bandpass and neutral density filter wheels while maintaining optical
alignment. A filter wheel can be changed in less than 60 seconds; typically it
requires about 30 seconds. Therefore, the user can quickly reconfigure the
illuminator to meet other test applications.
Additional features of the PI-4875 Precision Illuminator are the ability to
focus an image on the DUT and a monitoring detector to monitor the output of the
illuminator at the DUT. These two functions are also under computer control. For
image projection there is an arm that holds the desired image or target. This
image, when placed in the light path, is projected on to the device under test.
The image can be focused on the DUT by axial movement using a linear motion
stage. The output monitoring function is a mirror that directs light energy to a
detector for measurement. The mirror is not permanently in the light path but is
switched into the light path on computer command.
The Illuminator Support Instrumentation consists of the light source power
supply, the integrating sphere monitor/controller and the control electronics
for the control of the iris, target and focusing control, output monitor control
and the control for the bandpass and neutral density filter wheels. These units
are placed in a 19" cabinet with an AC Power Strip and included with the
illuminator. The units are rack mountable so they can be integrated into your
test system rack.
The software for the PI-4875 Precision Illumination Source functions under the
current versions of Windows 2000 or NT. The software controls the positioning of
the neutral density filter wheel and the selection of the desired bandpass
filter. This software also controls the aperture of the iris between fully open
to closed. The other functions controlled by the software are selecting the
mirror position for output luminance monitoring and selecting the target or
image for focusing on the DUT. The target focus is controlled via the software
by positioning the linear stage. The PI-4875 control software can be slaved to
the user’s system software, such as PI-DATS (Pulse Instruments’ System
Software) or LabView.