THORLABS EDU-SPEB1 User manual

EDU-SPEB1
EDU-SPEB1/M
Advanced Spectrometer Kit
User Guide

Advanced Spectrometer Kit
Page 1 MTN002263-D02 Rev C, August 26, 2015
Table of Contents
Chapter 1Warning Symbol Definitions ........................................... 2
Chapter 2Safety ................................................................................ 3
Chapter 3Introduction ...................................................................... 4
Chapter 4Setup ................................................................................. 5
4.1.ComponentsandPartsList.............................................5
4.2.ComponentAssembly....................................................8
4.2.1.LED Wiring ................................................................................ 10
4.3.SetupandAdjustment..................................................10
4.3.1.Light Source Setup.................................................................... 10
4.3.2.Prism Spectrometer Setup ........................................................ 11
4.3.3.Grating Spectrometer Setup ..................................................... 13
Chapter 5Spectrometer Theory ..................................................... 15
5.1.Introduction.................................................................15
5.2.WaveInterferencewithDoubleSlitsandGratings.......15
5.2.1.Double slit ................................................................................. 15
5.2.2.Grating Interference .................................................................. 17
5.3.DispersingPrisms.........................................................18
Chapter 6Teaching Tips and Experiments................................... 21
6.1.Exercise1:WavelengthMeasurementofThreeLinesin
theMercurySpectrum.................................................21
6.2.Exercise2:MeasuringtheIndexofRefractionofthe
PrismUsingaKnownSpectralLine...............................23
Chapter 7Regulatory ...................................................................... 25
7.1.WasteTreatmentisYourOwnResponsibility...............25
7.2.EcologicalBackground.................................................25
Chapter 8Thorlabs Worldwide Contacts ...................................... 26

EDU-SPEB1 & EDU-SPEB1/M Chapter 1: Warning Symbol Definitions
Page 2
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your device.
Symbol Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or Chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation

Advanced Spectrometer Kit
Page 3 MTN002263-D02 Rev C, August 26, 2015
Chapter 2 Safety
CAUTION
Optical gratings can be easily damaged by moisture, fingerprints, aerosols, or the
slightest contact with any abrasive material. Gratings should only be handled when
necessary and always held by the sides. Latex gloves or a similar protective covering
should be worn to prevent oil from fingers from reaching the grating surface. No
attempt should be made to clean a grating other than blowing off dust with clean, dry
air or nitrogen. Solvents will likely damage the grating's surface. Scratches or other
minor cosmetic imperfections on the surface of a grating do not usually affect
performance and are not considered defects.
!
!

EDU-SPEB1 & EDU-SPEB1/M Chapter 3: Introduction
Page 4
Chapter 3 Introduction
Optical spectroscopy has made a major contribution to the development of today's
concept of atomic and molecular structure and is indispensable as an analysis procedure
in research and industry. Astronomers can analyze the composition of distant stars and
environmental analysts can optically measure the composition of exhaust gases without
having to take samples. Each of these application areas has different requirements with
regard to the spectrometer to be used.
This kit includes parts to build two types of spectrometers, and can be easily set up by
students. These spectrometers can achieve very fine resolutions, allowing very close
spectral lines to be resolved, such as the sodium-D lines (spectral distance of 0.6 nm).
As the setup is very small, LEDs can also be analyzed, although so-called "superbright"
LEDs, which have a higher intensity than normal LEDs, are recommended. The included
LED bracket makes it very easy to install the LEDs in the setup. Other light sources,
such as incandescent lamps, energy-saving lamps (compact fluorescent tubes), mercury
vapor lamps, and lasers can also be analyzed by the spectrometer
The experiment package contains the following wavelength-dispersive elements:
A reflective grating with 600 lines/mm.
A reflective grating with 1200 lines/mm.
An equilateral dispersing prism.
Additional gratings and prisms are available, which can be purchased separately from
Thorlabs. Contact [email protected] for more information.
The supplied gratings are called blazed gratings, which means that the reflective layer is
arranged diagonally. The great advantage of this is that the highest intensity is not in the
zeroth diffraction order, which is directly in the incoming beam path and thus not of
interest, but rather in a higher order, to the side of the incident beam. In the case of the
gratings used in this kit, the first order is the most intense. However, you can also easily
observe higher orders with the setup (up to 5 with the grating 600 lines/mm). In addition,
blazed gratings function in the same way as normal gratings, so all of the standard
grating calculations and equations apply. Thus, for teaching purposes, the difference
need not be addressed, as there is no difference in the equations that are relevant for the
classroom.

Advanced Spectrometer Kit
Page 5 MTN002263-D02 Rev C, August 26, 2015
Chapter 4 Setup
4.1. Components and Parts List
In cases where the metric and imperial kits contain parts with different item numbers,
metric part numbers and measurements are indicated by parentheses unless otherwise
noted.
1 x LEDMF
LED Mount
1 x LEDWE-15
Epoxy Encased White
LED, Package of 5 2 x ACL2520U
Ø1" Aspheric Condenser
Lens, f = 20 mm
2 x FMP1(/M)
Ø1" Setscrew Lens Mount
1 x LB1471
Ø1" Focusing Lens,
f = 50 mm
2 x LMR1(/M)
Ø1" Threaded Lens Mount
1 x VA100(/M)
Adjustable Slit
1 x LB1676
Ø1" Imaging Lens,
f = 100 mm
1 x GR25-1205
1200 lines/mm Reflective
Grating

EDU-SPEB1 & EDU-SPEB1/M Chapter 4: Setup
Page 6
1 x GR25-0605
600 lines/mm Reflective
Grating
2 x CH1A
Grating Mount
1 x PS858
Equilateral Dispersing
Prism
1 x KM100PM(/M)
Kinematic Prism Mount
1 x PM3(/M)
Clamping Arm for Prism
Mount 1 x EDU-VS1(/M)
Viewing Screen
1 x MB1824 (MB4560/M)
Optical Breadboard,
18" x 24" (45 cm x 60 cm)
1 x RDF1
4 Breadboard Feet 9 x TR3 (TR75/M)
Ø1/2″(Ø12.7 mm) Optical
Post, 3" (75 mm) Long
9 x PH3 (PH75/M)
Ø1/2" (Ø12.7 mm) Post
Holder, 3" (75 mm) Long
1 x TR2 (TR50/M)
Ø1/2" (Ø12.7 mm) Optical
Post, 2" (50 mm) Long
1 x PH2 (PH50/M)
Ø1/2" (Ø12.7 mm) Post
Holder, 2" (50 mm) Long

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Page 7 MTN002263-D02 Rev C, August 26, 2015
6 x BA1(/M)
Post Holder Base,
1" x 3" x 3/8" (25 mm x
75 mm x 10 mm)
4 x BA2(/M)
Post Holder Base,
2" x 3" x 3/8" (50 mm
x 75 mm x 10 mm)
1x TPS5
Laser Safety Screen,
12" x 12"
(305 mm x 305 mm)
Imperial Kit Hex Keys, Ball Driver, and Screws
Imperial Kit Hex Keys: 3/32", 0.050",
5/64", and 1/8" 1 x BD-3/16L
Balldriver for 1/4"-20 Screws
Imperial Screws:
10 x 1/4"-20 Cap Screw, 1/2" Long
12 x 1/4"-20 Cap Screw, 5/8" Long
4 x 1/4"-20 Cap Screw, 3/4" Long
12 x M6 Washers
4 x #1/4 Nuts
1 x 8-32 Cap Screw, 1/4" Long
Metric Kit Hex Keys, Ball Driver, and Screws
Metric Hex Keys: 1.3 mm, 2 mm,
and 3 mm 1 x BD-5ML
Balldriver for M6 Screws
Metric Screws:
10 x M6 Cap Screw, 12 mm long
12 x M6 Cap Screw, 16 mm Long
4 x M6 Cap Screw, 20 mm Long
12 x M6 Washers
4 x M6 Nuts
1 x M4 Cap Screw, 6 mm Long

EDU-SPEB1 & EDU-SPEB1/M Chapter 4: Setup
Page 8
4.2. Component Assembly
First, mount all of the lenses in the LMR1(/M) and FMP1(/M) mounts as specified below
and screw each mount to a Ø12.7 mm post. Next, place each post into a PH3 (PH75/M)
post holder and attach a BA1(/M) post holder base.
1. LB1676 and LB1471 lenses in LMR1(/M) mounts (Figure 1a).
2. ACL2520U condenser lenses in FMP1(/M) mounts (Figure 1b).
3. Attach each mount to a TR3 (TR75/M) post, place into a PH3 (PH75/M) post
holder, and attach a BA1(/M) base using a 1/2" long 1/4"-20 (12 mm long M6)
cap screw.
Figure 1 : Ø1” Lenses in LMR1(/M) (a) and FMP1(/M) (b) Mounts, on Ø1/2” Posts
Next, mount the VA100(/M) slit and LEDMF led mount to posts in a similar fashion:
1. VA100(/M) adjustable slit on TR3 (TR75/M) post (Figure 2a)
2. LEDMF LED bracket on TR3 (TR75/M) post (Figure 2b)
3. Place each post in a PH3 (PH75/M) post holder. Attach a BA1(/M) base to the
slit, and a BA2(/M) base to the LED holder using 1/2" long 1/4"-20 (12 mm long
M6) cap screws.
The LED mount also has interchangeable adapters for smaller LED sizes.
Next, mount the prism on the KM100PM(/M) prism mount and the grating in its CH1A
mount:
1. GR25-1205 and GR23-0605 gratings each in a CH1A (Figure 3a)
2. PS858 Prism on KM100PM(/M) (Figure 3b)
3. Attach each mount to a TR3 (TR75/M) post, place into a PH3 (PH75/M) post
holder, and attach BA2(/M) bases using 1/2" long 1/4"-20 (12 mm long M6) cap
screws.
a) b)

Advanced Spectrometer Kit
Page 9 MTN002263-D02 Rev C, August 26, 2015
Figure 2 : Adjustable Slit VA100(/M) (a) and LEDMF LED Mount (b) on Ø1/2” Posts
Figure 3 : Grating in CH1A Mount (a), and Prism in KM100PM(/M) Mount (b), both on Ø1/2”
Posts
b)a)
b)
a)

EDU-SPEB1 & EDU-SPEB1/M Chapter 4: Setup
Page 10
Mounting the KM100PM(/M) or the CH1A on a Post
Instead of a threaded hole for mounting, the KM100PM(/M) and the CH1A each contain
a counterbored hole. To post mount these parts, first remove the setscrew from the post
that you are using. Insert an 8-32 (M4) cap screw through the counterbored hole in the
universal mount, and tighten it into the post on the other side of the hole.
4.2.1. LED Wiring
The LED included with the kit can be powered using a simple battery or DC power
supply. A resistor is also needed in the circuit in order to avoid damaging the LED. Wire
the LED in series with the battery and resistor by soldering or using alligator clips. The
ideal resistance, R, in ohms, may be calculated using the following formula, where Iis
the specified LED operating current, VLis the specified LED operating voltage, and Vsis
the battery or power supply voltage.Use a resistor with the lowest value available that is
still greater than the calculated resistance.
ܴൌ
ܸ
ௌെܸ ௅
ܫ
For example, using the LEDWE-15 LED included with the kit, a 4.5 V battery and a 68 
resistor wired in series will produce a voltage drop of 3.2 V across the LED and a current
of 20 mA, which will sufficiently power the LED.
4.3. Setup and Adjustment
4.3.1. Light Source Setup
Take the two condenser lenses, the standard lens with focal length f = 50 mm, and the
slit and assemble the components as shown in Figure 4, using 5/8" long 1/4"-20 (16 mm
long M6) cap screws and M6 washers to attach components to the breadboard.. Next,
position your light source at the end of the breadboard. The goal is to focus as much light
as possible from the light source on the slit. Depending upon the form and the size of
your light source, the standard 50 mm focal length lens may be omitted.
Place the first condenser lens directly behind the light source, the second at a distance of
about 40 mm behind the first (curvature facing inward). The function of these lenses is to
“catch” as much light intensity as possible. The standard lens with f = 50 mm should now
be positioned at a distance of 50 – 60 mm behind this. It will then focus the light on the
slit. Place it in the beam path after approximately an additional 50 mm (focal length of the

Advanced Spectrometer Kit
Page 11 MTN002263-D02 Rev C, August 26, 2015
lens). As the light sources used usually are not ideal point light sources, you often see a
small image of the light source in this focus point (e.g. coil filament, LED-chip, Hg-tubes).
This can be useful for focusing.
Figure 4 : Beam Path from Light Source to Slit
Next, focus the image of the slit on the grating. For this, place the second standard lens
(f = 100mm) in the beam path, as shown in figure 5. The distance from the slit should be
10-15 cm. Insert the dispersive element (grating, prism) after the lens after an additional
10-15 cm.
Place the TPS5 laser safety screen on the breadboard as shown in figure 4. This will
shield the viewing screen from stray light emitted by the light source.
4.3.2. Prism Spectrometer Setup
When you place the prism into the beam path, ensure that you do not direct the beam
through the matte side of the prism. Instead, this side of the prism should be facing
between the black laser safety screen and the white viewing screen. Turn the prism until
you see a sharp spectrum on the screen and make any necessary adjustments with the
lenses and the distance of the screen. The slit, prism, lenses, and screen are shown in
Figure 5, and the complete prism spectrometer setup is shown in Figure 6.
5-6 cm 4 cm 5-6 cm

EDU-SPEB1 & EDU-SPEB1/M Chapter 4: Setup
Page 12
Figure 5 : Beam Path from Slit to Prism to Screen
To obtain an optimum image, change the slit width. The further the slit is opened, the
brighter/more intense the image becomes, and the tighter it is closed, the sharper the
image becomes.
10 - 15 cm 10 - 15 cm

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Page 13 MTN002263-D02 Rev C, August 26, 2015
Figure 6 : Prism-Based Spectrometer Complete Beam Path
4.3.3. Grating Spectrometer Setup
The grating-based spectrometer setup is the same up to the f = 100 mm lens (see
section 4.3.1, above). You must now focus the light on the grating. The complete
grating-based spectrometer setup is shown in Figure 7. The illustration shows the first
order to the right of the zeroth order of the 600 lines/mm grating.
Place the screen so that you can observe the spectrum. Once again, make fine
adjustments to the lenses or screen for a sharp image.

EDU-SPEB1 & EDU-SPEB1/M Chapter 4: Setup
Page 14
Figure 7 : Grating-Based Spectrometer Complete Beam Path
Tip: Due to the sawtooth-like grating structure, the number of observable orders
depends upon the direction the grating has been rotated in relation to the optical axis.
On one side of the zeroth order, you obtain a particularly intense image in the first order.
This image is visible even with weak room lighting.
On the other side of the zeroth order, the spectra are less intense (similar to "normal"
non-blazed gratings). In order to view this image, the room should be darkened.
However, you can even observe the 5th order on this side with the grating with 600
lines/mm. Also note that the red/orange range of the 3rd order overlaps the blue/violet
range of the 4th order.
Tip: If the grating or the screen is moved or rotated somewhat, the lens between the slit
and the grating must also be adjusted accordingly. Move it back and forth somewhat in
the beam path until a sharp image is obtained.
Tip: If you place a white sheet of paper on the screen (bleached), you can even observe
UV lines (if present). This is due to the fact that the paper contains bleaches that
fluoresce (absorb UV light and emit visible light) to make the paper look brighter under
daylight.

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Page 15 MTN002263-D02 Rev C, August 26, 2015
Chapter 5 Spectrometer Theory
5.1. Introduction
A number of experiments can be conducted with this spectrometer kit. First, various
types of light sources and spectra can be analyzed. Suitable light sources include:
Incandescent Lamps
Compact Fluorescent (Energy Saving) Lamps
LEDs
Gas Discharge Tubes Including Mercury or Sodium Vapor Lamps
The most important parameters or objects of study of the spectrometer are:
Qualitative:
Relationship between slit width and spatial resolution.
Relationship between slit width and intensity of the spectrum.
Relationship between grating constant and spatial resolution.
Observation of the differences between the diffraction orders.
Quantitative (listed here as an example):
Calculation of the wavelengths of spectral lines by means of the grating
equation with the aid of a grating.
Calculation of the refractive index of the prism glass with the prism.
Many other applications are possible, which can also be interdisciplinary. An example of
this is the examination of the absorption of chlorophyll. For this, one could first examine
the spectrum of an incandescent lamp and then place a cuvette with dissolved
chlorophyll in the beam path. As a result, one sees which color components are
absorbed the most by the chlorophyll.
5.2. Wave Interference with Double Slits and Gratings
5.2.1. Double slit
Consider a set of slits (double slit), as shown in Figure 8a and 8b. The dimensions of the
slits should be smaller than the wavelength of the incoming light.

EDU-SPEB1 & EDU-SPEB1/M Chapter 5: Spectrometer Theory
Page 16
Figure 8 : Double Slit Showing (a) Waves Emanating from the Two Point Sources and (b)
Path Length Difference Between the two Slits
Light hits the double slit in the form of a planar wavefront (Figure 8a). In accordance with
Huygens' principle, each slit is then the origin of an elementary spherical wave, also
called an elementary wave for short. These two elementary waves spread out behind the
slit and overlap. Areas of constructive and destructive interference are created, which
result in bright and dark areas when an image is viewed on a screen. We consider any
point P behind the slits, which is so far removed that we can observe the wave trains
emanating from the slits as parallel (Figure 8b). The path difference Δsbetween them is
Δs = g  sin  . With the aid of geometrical optics, we can then easily see that we obtain
constructive interference for integral multiples of the wavelength and destructive
interference for half-integral multiples.
For maxima, the following must be true:
sin , 0,1,2,...
n
sg n n



  
For minima, the following must be true:
1
sin , 0,1,2,...
2
n
sg n n 

    


This is also easy to understand intuitively, because at points of maximum intensity,
"wave peak meets wave peak" if the phase difference of the wave trains is one
wavelength and "wave peak meets wave trough" if it is one half wavelength.
a)
g

∆s
P
P
b)

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Page 17 MTN002263-D02 Rev C, August 26, 2015
5.2.2. Grating Interference
We can model a grating as a number of slits, N, as sketched in Figure 9.
Figure 9 : Path Length Differences Between Grating “Slits”
For the sake of clarity, we will refrain from a detailed, theoretical explanation of gratings,
but can still make the following conclusions:
Intensity:
The intensity I0of the interference pattern becomes greater as more slits are illuminated:
If the amplitudes of the individual wave trains overlap, the intensity is I = (N  A)2, as the
output amplitudes A0of the electrical field vectors add up. (note that intensity results
from the square of the field amplitudes).
Interference:
As is the case with the double slit, the differences in pathways of the wave trains from
the individual slits must also be an integral multiple of the wavelength of the incident light
in the case of the grating in order to obtain constructive interference. For the maxima, the
following grating equation is in effect:
sin , 0,1,2,...
n
nn
g




Here, gis the grating spacing,
 is the wavelength of the incident light, and nthe
diffraction order observed under the angle

n. In conclusion, the spectral separation at
the grating results from the diffraction by the slits.
∆s
g
n


2n
3n
4n
P

EDU-SPEB1 & EDU-SPEB1/M Chapter 5: Spectrometer Theory
Page 18
From this correlation, it is immediately obvious that the angle 
ndepends upon the
wavelength of the incident light. If we examine light that is composed of many
wavelengths, as is the case with our light sources to be examined, these wavelengths
are spatially split, and we obtain a spectrum. These characteristics apply regardless of
whether the grating works in transmission or reflection. In addition, it is apparent that
larger wavelengths also result in a larger deflection angle (as opposed to a prism – here
the behavior is reversed).
Resolution:
The spatial resolution Aof a spectrometer can be derived as follows:
A
nN





Once again here, nis the diffraction order, Δ  is the smallest observable wavelength
difference, and Nis the number of illuminated slits. In order to determine Δ
 , one can
observe in the present setup, for example, whether known spectral lines (such as the
orange lines in the mercury spectrum) can be perceived separately.
The formula above immediately reveals that the resolution increases with increasing
diffraction order and increasing number of illuminated slits. In addition, one can
demonstrate that the resolution increases as the slit width of the illustrated slit becomes
smaller. In accordance with the grating equation:
sin , 0,1,2,...
n
nn
g




it becomes clear that the angle widening of the image increases with increasing fineness
of the grating (meaning decreasing the grating spacing g) and the resolution is therefore
improved. It is therefore interesting to compare gratings with various grating constants1.
5.3. Dispersing Prisms
“Dispersion” in the context of a prism means that the angle
of refraction of light is highly dependent on wavelength.
This is the case in so-called dispersion prisms. Such
prisms have an equilateral triangle as a cross-sectional
area and consist of suitable glasses with high dispersion,
e.g. crown glass. Light is directed at one side of the prism.
It is refracted once upon entering the prism at the air/glass
interface and finally once again upon exiting the glass/air interface.
1In this kit, g = 1/(600 lines/mm) vs. g = 1/(1200 lines/mm)

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Page 19 MTN002263-D02 Rev C, August 26, 2015
As the refractive index depends upon the light wavelength, Different wavelengths of light
are refracted at different angles, and are thus spatially separated.
Figure 10 : Angle of Minimum Deviation in an Equilateral Prism
The angle of minimum deviation  (see Figure 10) with incident angle  and refractive
angle
 is obtained if  =  . Here, the beam within the prism runs parallel to the base
of the prism. With the aid of geometry, one can derive the following:
60 2 60

 

 
In this case, the law of refraction can be written as:
60
sin 2
sin30
n







Therefore, if one measures the minimal deflection angle, which can be sharply focused
and thus determined well, one can determine the refractive index of the prism material at
an observed wavelength (see sample exercise in Chapter 6.2). 2
Refraction in a Prism
The refractive index of the prism material depends upon the wavelength of the incident
light. Since the deflection angle is ultimately determined by the refractive index, the
various wavelengths can be separated spatially. This is a normal dispersion in the glass,
meaning that the refractive index increases with reduced wavelength (blue light is
refracted more than red). This is particularly interesting as the deflection in the grating
behaves exactly in the opposite manner (smaller deflection angle for blue light). Figure
2The supplied prism has an angle of minimum deviation of 47.9° at 633 nm. See the graph below
for index of refraction vs. wavelength.
60°


