Thermo Finnigan SpectraSYSTEM UV6000LP, Reference Manual

Page: 27 / 137

January 2004 Thermo Electron 1-3
The optical bench contains a beam combiner, focusing lens, filter
wheel, flowcell, beam shaper, folding mirror, and grating. The beam
combiner reflects the light coming from the tungsten - halogen lamp
so that it is parallel to and coincident with the light from the
deuterium lamp. The combined beam is then focused on the inlet
window of the flowcell through the filter wheel. The standard filter
wheel has two positions. Position 1 (open) is used for normal
operation. Position 2 contains a cuvette filled with a holmium oxide /
perchloric acid solution, (NIST Traceable), for wavelength accuracy
verification and calibration.
P
D -
Z
01
0/
S
T
Flow Cell
Folding
Mirror
Beam
Shaper
Fixed
Grating
1 x 512
Photo Diode Array
Focusing Lens
Deuterium Lamp
Beam Combiner
Filter Wheel
Tungsten-halogen Lamp
Figure 1.1 The UV6000LP optical system
The light focused on the inlet window of the flowcell travels down
the cell, is partially absorbed by the sample flowing through the cell,
and exits into the beam shaper. The beam shaper is a fiber bundle. Its
entrance aperture is circular to collect light from the flowcell. The
other end of the bundle is arranged to produce a narrow “slit” of light
for the grating. The beam shaper transfers all of the light to the
grating for greater light throughput than the mechanical slit used in
conventional photodiode array detectors.
The folding mirror between the output of the beam shaper and the
grating is used to shorten the optical bench and thus reduce the
physical size of the detector. The spectrum from the grating is
focused on the 512 element photodiode array. Since the spectrum of
light falling on the array is 611 nm, (190 to 800 nm), the effective
spacing of the diodes is 611 nm/512 = 1.2 nm. Firmware resident in
the detectors’ CPU PCBA automatically interpolates diode intervals
to arrive at integer wavelengths.