Download Instrumentation and Techniques in Optical Spectroscopy

Instrumentation and Techniques
in Optical Spectroscopy
Chemical Physics Course
Instrumentations and techniques
• A Spectroscopy experimental set-up
• Wavelength selection
– Monochromators
– Filters
• Detectors
– PM, MCP, photodiods, CCD
• Measuring instruments
– Photon counter, lock-in, boxcar, TCSPC
Typical Optical spectroscopy Experiment
Photomultiplier
Sample
Light sourse
or Diod
Wavelength
Wavelength
selector
selector
Detector
Lamp
laser
Filter
Monochromator
Signal averaging
Photon counting
Boxcar
Lock-in-Amplifier
Xenon lamp and typical housing
Spectral output of Xenon lamp
Optical Materials
Material used to construct spectrometer optical components must be
chosen with operating wavelength range taken into account.
Diffraction Grating
Dispersion
The diffraction grating causes interference
between waves reflected from its surface, and
constructive interference occur when:
nλ = d (sin θ − sin φ )
Where n=1,2,.. is the diffraction order
λ is the wavelength of the diffracted radiation
d is the distance between the grooves,
θ is the angle if incidence
φ is the angle of the emergence of the beam
Example:
Influence of the number of groves /m on the resolution.
Consider a first order diffraction (n=1)
and an angle of incidence θ =300
d= 1000 nm
(1000 line/mm)
d= 10000 nm
(100line/nml)
λ= 500 nm 0
26,7
λ= 400 nm 5,7
27,4
Δφ
0,7
5,7
It can be seen that the DG with a larger number of groves/mm will give a
larger wavelength separation
Monochromators based on a plane or concave grating
Diffraction grating blazing
Efficiency of two –ruled grating blazed for different wavelengths
Spectral resolution
Emission spectra of pterphenyl collected
with a spectral
resolution of 0.5 and
10 nm
Polarisation dependence
Grating efficiency
for different (S and
P) polarisation
Optical Filters
Types of filters
•
•
•
•
Neutral density filters
Bandpass filters
Long pass filters
Interference filters
Neutral density filters
Neutral Density Filters
Graduated Neutral Density
Optical Density (O.D.) =-log (I/I0)
Bandpass filters
and
Long pass filters
Band pass filters
Interference filters
Spectral Response of PMT
Multichannal plate Photomultiplier
Time response of PMT
Characteristics of PMT
CCD detectors
Time correlated Single Photon Counting (TCSPC)
TCSPC data
TRSPC data
TRSPC data
Fluorescence decays of POPOP in n-octanol at 295 K and the
instrumental response function( IRF)
The Streak Camera
Time and spectral resolution