Biomedical Engineering Reference
In-Depth Information
1000
QTH
100
Hg
10
Xe
1
250
500
750
1000
1250
1500
1750
2000
Wavelength (nm)
Fig. 1.1
Example emission spectra of xenon arc lamp (Xe), mercury arc lamp (Hg), and quartz
tungsten halogen lamp (QTH) (Reproduced with permission from Newport)
the light source. When broadband light is dispersed by the grating and incident onto
the DMD, the spectrum and the intensity of the output light beam can be selectively
controlled by turning on or off the position and number of the micromirrors. Such
kind of light source is versatile, rapidly programmable, and easy to use, particularly
for absorption/transmission spectroscopy and spectral imaging.
Supercontinuum light source is a new type of broadband light source. It is
generated by propagation of high-power pulse through nonlinear media. Although
the phenomenon of supercontinuum light generation was first observed in 1970,
it is only until very recently that supercontinuum light source products became
commercially available that benefitted from the development of femtosecond-pulsed
lasers and photonic crystal fibers (PFC) [
15
,
16
]. An example spectrum from a super-
continuum light source is shown in Fig.
1.2
[
16
]. The supercontinuum generation
is determined by dispersion of the nonlinear media, the pumping wavelength, the
pulse length, and the peak power. Newest supercontinuum light source is capable
of generating several watts of total optical powers in the broad visible to NIR
wavelength range [
17
].
1.2.1.2
Lasers (Gas, Solid State, Dye, Semiconductor, Fiber)
Broadband light sources are commonly used for absorption/transmission/reflectance
spectroscopy. Lasers are often used for fluorescence and Raman spectroscopy.
Laser sources can be easily monochromatic, naturally suitable for Raman excitation.
Laser sources can also be highly collimated and with high intensity, thus, can be
efficiently coupled into optical fibers for convenient delivery. Based on the lasing
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