Laser Raman Spectrometers

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Laser Raman Spectrometers NRS-3000 Series Part
II.
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Laser Excitation

• A high performance, narrow line-width,
  solid-state diode laser of 532 nm is standard.
• A variety of diode and gas lasers are also
  available with a number of alternative excitation
  wavelengths and output powers.
• Laser line filters used for diode lasers are
  selected to provide monochromatic radiation with
  minimum power loss.
• High power laser systems may require a
  pre-monochromator system to be installed prior to
  the automated source optics.

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Laser Sources NRS-3100 Standard model Visible
- NIR NRS-3200 Multi-configuration model UV -
NIR NRS-3300 Advanced applications model UV -
NIR
Applicable Laser Sources
UV
NIR
244 nm 257 nm Ar Laser
785 nm Deep Red Diode Laser
488 nm Blue Ar Laser
514.5 nm Ar Laser
632.8 nm Red He-Ne Laser
532 nm Green Diode Laser
325 nm He-Cd Laser
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Why use different lasers?
Raman intensity depends on excitation wavelength
but Raman shift stays the same
Intensity
Excitation n0
Red changed to green laser Scattering intensity
increased but position unchanged
Raman shift in cm-1 (Kaisers)
0
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Multi Laser Benefits
532 nm excitation
785 nm excitation
1800
300
500
1000
1500
Raman shift cm-1
532 nm laser excitation generates a high
fluorescence background for the sample of white
wine which is greatly reduced by switching to 785
nm excitation
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JASCO NRS-3000 Series
Changing excitation lasers can be
time-consuming. The NRS-3000 Series uses
automated input optics to select between 6
different lasers without requiring laser path
re-alignment.
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Specifications Sample compartment Safety
feature Interlock system Note The interlock
system is a mechanism that actuates the shutter
to prevent the laser beam from entering the
sample compartment when the sample compartment
door is opened. Micro sample compartment Laser
beam irradiating/Raman light focusing
direction Irradiates sample perpendicularly
from above/focuses light perpendicularly above
the sample (back scattering system) Laser beam
irradiating system With focusing fine
adjustment mechanism Beam diameter Minimum 1
?m Beam splitter Ratio between Raman light
transmission and laser beam reflection
73 Objective lens standard x100, x20, x5 up
to 6 optional objectives available
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An accessible sample compartment
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Sample compartment
Sets the objective lens by turning the holder. A
maximum of 6 lenses can be mounted.
Sample plate
Moves the stage to back and front Moves the
stage from side to side
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Interchangeable objective lenses
x5
x20
x100
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Ease of operation
Simply insert the sample, focus the laser and
collect data!
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Precise sample stage control
Optional automated X-Y-Z stages using PC control
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Specifications TV monitor TV monitor Permits
simultaneous observation of the sample surface,
laser spot and confocal aperture image
(aperture diameter 50, 200 and 3000 ?m
selectable) TV camera Color CCD camera Image
magnification 2000x or more (when 100x
objective lens is used) Display unit Real-time
display on CRT by video capture Sample
illumination Epi-illumination Sample
compartment accessory Neon lamp For wavenumber
correction (permits independent measurement or
simultaneous measurement with Raman
spectrum)
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High quality sample view
Standard color CCD-TV camera for sample viewing
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High quality sample view
Optional binocular or trinocular optics available
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High quality sample view
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Precision sample stage control
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Specifications Raman light inlet Raman light
introducing system Parallel beam transmitting
system (achromatic lens used) Rayleigh cutoff
filter Holographic notch filter (equivalent
to O.D. 6, for 532 nm) Spectrograph Optical
arrangement Single dispersive Wavenumber drive
system Direct drive type Diffraction
grating Holographic diffraction grating 1800
lines/mm (standard) (options 2400 lines/mm,
1200 lines/mm, 600 lines/mm) Working wavelength
range 220 to 1100 nm Absolute wavenumber
accuracy ? 1 cm-1 Diffraction grating
changeover Maximum of 3 gratings Measurable
wavenumber range 50 to 8000 cm-1 or
more (Raman shift wavenumber 532 nm
excitation) Wavenumber resolution Approx. 1
cm-1 Specifications of low wavenumber measurement
attachment (filter monochromator) Working
wavenumber range 220 to 1100 nm
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NRS-3000 Spectrograph

• The NRS-3000 spectrograph is a single grating
  polychromator of modified Czerny Turner design
  with a 300 mm focal length and a high-precision,
  direct drive.
• JASCO offers a choice of gratings with 4
  different rulings, from the broadest spectral
  range in the red to the highest resolution in the
  green.
• As an option, NRS-3000 can be fitted with 3
  software interchangeable gratings.

Avoid fluorescence
Grating choices 2400,1800,1200, 600 lines/mm
High sensitivity and extended measurement range
High resolution measurement
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Grating Dispersion and the CCD

• A CCD detector is essentially an array of
  detectors (pixels) on a chip. A coarsely ruled
  grating will give more spectral range over the
  detector but the spectra will be less well
  resolved in pixels more than 1 pixel is required
  to properly define a peak.
• Longer wavelengths (high Raman shift, or red
  excitation) result in greater dispersion and thus
  higher resolution, choosing two lasers may
  require two different gratings to give comparable
  resolution.
• With a high resolution grating, the complete
  spectrum wont fit on the range of CCD pixels, it
  is then necessary to acquire several spectra at
  different grating angles and splice them via
  software.