Advanced Spectroscopy Technique for Biomedicine - Biomedical Optical Imaging Technologies: Design and Applications - page 18

Tabl e 1. 3 Summary of CCD types and their applications

Peak QE/

Light Dark

CCD type wavelength Applications level current Cooling type

Front
illuminated

47% at 700 nm Absorption

Transmission
Reflection
Elastic scattering

High 1 Thermoelectric

(two stages)

Front
illuminated
open circuit

47% at 700 nm Analytical

luminescence
Analytic Raman

Medium 1 Thermoelectric

(four stages)

Back
illuminated

97% at 500 nm Research

luminescence
Research Raman

Low 1-1:5 Thermoelectric

Liquid Nitrogen

Back
illuminated,
deep depletion

95% at 800 nm Research

luminescence
Research Raman

Ultralow 100 Thermoelectric

Liquid Nitrogen

Fig. 1.9 Displacement of slit
image with respect to the
vertical position away from
the center of the slit

6

4

2

532 nm, f1 = f2 = 85 mm

785 nm, f1 = f2= 120 mm

0

785 nm, f1 = f2 = 85 mm

-2

-4

-6

0 0.1 0.2 0.3

Displacement, mm

For spectrographs with short focal lengths, this obliqueness causes significant
distortion that can affect the performance of the detector. This image aberration
causes two problems for hardware binning of CCD detectors: (1) It decreases the
spectral resolution and (2) it decreases the S/N ratio. It also causes problems in
wavelength calibration. The manufacturer (Kaiser) of the HoloSpec spectrograph
suggested a combination of hardware and software binning in which the neighboring
pixels are hardware binned, then shifted to the appropriate number of pixels and
summing them up with software. Recently, we proposed a novel method for full-
chip hardware binning by pretreatment of the slit [ 11 ]. Details will be discussed in
Sect. 1.3.1.6 .