THORLABS SLS201L User manual

SLS201L(/M)
SLS202L(/M)
Stabilized Tungsten
Light Sources
User Guide

Compact Stabilized Light Sources
Table of Contents
Chapter 1 Warning Symbol Definitions ........................................... 1
Chapter 2 Safety................................................................................. 2
Chapter 3 Product Overview ............................................................. 3
3.1. Planck's Law and Black Body Radiation .........................3
3.2. Tungsten Light Source ...................................................4
3.3. Spectrum ......................................................................5
3.4. Optical Configuration....................................................5
3.5. Optional Collimator.......................................................6
3.6. Output Stabilization ......................................................7
Chapter 4 Operation........................................................................... 8
4.1. Part List ........................................................................8
4.2. Setting Up on a Working Surface ...................................8
4.3. Switching on the Light Source........................................9
4.4. Filter Holder................................................................10
4.5. Front Fiber Coupler .....................................................10
4.6. Adjusting Fiber Coupler Position..................................11
4.7. Collimating Accessory (Optional) .................................11
4.8. Application Ideas ........................................................12
4.9. Bulb Module Replacement ..........................................13
Chapter 5 Specifications .................................................................16
Chapter 6 Mechanical Drawing....................................................... 17
Chapter 7 Certifications and Compliances....................................18
Chapter 8 Regulatory....................................................................... 19
Chapter 9 Thorlabs Worldwide Contacts....................................... 20

Compact Stabilized Light Sources Chapter 1: Warning Symbol Definitions
Rev F, October 14, 2021 Page 1
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
Caution: Spinning Blades May Cause Harm

Compact Stabilized Light Sources Chapter 2: Safety
Page 2 CTN002682-D02
Chapter 2 Safety
The lamp comes with a switching power supply compatible with voltages from 100
to 240 VAC. There is no need to change the fuse.
WARNING
Do not operate this device in explosive environments.
WARNING
Do not operate this device in wet or damp conditions.
WARNING
Do NOT look directly at the light source beam during operation. Do NOT place
hand or body part in the light beam as this may cause burning.
CAUTION: HOT SURFACE
The housing of the lamp housing can get very hot during operation.
Extensive contact may cause burning.
WARNING: HOT SURFACE
The temperature of the bulb may reach a few hundred ˚C during operation.
Always wait for at least 10 minutes for the bulb module to cool down before
performing a bulb module replacement. Always wear gloves when handling bulb
modules.

Compact Stabilized Light Sources Chapter 3: Product Overview
Rev F, October 14, 2021 Page 3
Chapter 3 Product Overview
3.1. Planck's Law and Black Body Radiation
A black body is an object that absorbs all incident electromagnetic radiation (e.g.
light), no light passes through or is reflected. However, despite the name, a black
body will also emit electromagnetic radiation. The radiation of a black body in
thermal equilibrium is described by Planck’s Law
(,) = 2

1
 
1
Where I is the radiated power per unit area of emitting surface per unit wavelength
at temperature
T ; K is the Boltzmann constant, h is the Planck constant, and c is
the speed of light.
By measuring the spectrum of the black body radiation, we can calculate the
temperature of this black body. Figure.1 shows the radiated power per unit area I
as a function of wavelength at various temperature.
Figure 1 Black body radiation at different temperatures
In real life, broadband light sources may vary widely from the ideal black body in
terms of the frequency and intensity of the light emitted. By comparing the light
source to an ideal black body at a given temperature, one can characterize the
light source by the temperature of the black body radiator which has the same
chromaticity, which is known as the color temperature of the light source

Compact Stabilized Light Sources Chapter 3: Product Overview
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3.2. Tungsten Light Source
A tungsten light source is a form of an incandescent lamp. During operation, a
current flows through the Tungsten filament, which will heat up to around a couple
of thousand Kevin. Tungsten emits visible and infrared light at this temperature,
creating a light source that can be approximated by a black body radiator.
SLS201L is a light source known as Quartz Tungsten Halogen (QTH) light sources.
In such a light source, the Tungsten filament is sealed in a quartz envelope with
inert gas and halogen mixture filled in the bulb. Tungsten atoms evaporated from
the filament during operation will hit the gas atoms and then bounce back to the
filament, thus lowering the overall rate of filament evaporation. The halogen in the
gas mixture will also react with tungsten deposited on the inner surface of the bulb
and form tungsten halide, which evaporates more easily back to the gas mixture.
When tungsten halide gets near the filament, it dissociates at the high temperature
of the filament, creating a gradient in the concentration of tungsten. Such flow is
called the “tungsten-halogen cycle”. It effectively “pumps” the tungsten back to the
filament, prolonging the life of the light source and reducing darkening of the bulb.
SLS202L is a Tungsten filament light source for IR applications. It operates at a
lower color temperature thus generating more IR output. The filament is sealed
behind a Sapphire window which transmits IR .better than quartz. A gold reflector
is also place behind the filament which reflects the longer wavelength thus provide
higher output in the NIR to MIR range.
Figure 2 shows the structure of the tungsten bulb used in SLS201L and SLS202L
stabilized light sources. For SLS201L, the filament is sealed in a Quartz Envelope.
For SLS202L, the filament is sealed in a cavity with a sapphire protective window
on top of it. There is a gold reflector inside the cavity which reflect out all the IR
light generate from the filament.
Figure 2 Structure of the Tungsten Halogen bulb used in SLS201L/SLS202L
Quartz Envelope
Tungsten Filament
Tungsten Filament
Sapphire Window
Gold reflector
SLS202L Bulb
SLS201L Bulb

Compact Stabilized Light Sources Chapter 3: Product Overview
Rev F, October 14, 2021 Page 5
3.3. Spectrum
The SLS201L tungsten halogen light source generates visible to IR output as far
as 2600 nm, with a color temperature of 2796 K. The SLS202L generates output
from 450 to 5500 nm with a color temperature of 1900 K. Figure 3 shows the typical
output spectra of SLSL201L and SLS202L compared to a theoretical black body
spectrum at the corresponding temperature.
Figure 3 Typical Spectra
3.4. Optical Configuration
SLS201L/SLS202L are Tungsten Light Sources. The bulb is placed inside the
housing, at the back focus of the 1st lens. The lens roughly collimates the output
from the bulb and then a 2nd lens focuses the collimated beam into a multimode
fiber patch cable, providing a fiber coupled broadband light source. Figure 4 shows
the outline of beam path in SLS201L and SLS202L.
Figure 4 Basic Optical Configuration of SLS201L/SLS202L
The bulb and the collimating lens is located in the main body of the light source
while the focusing lens is placed in a removable fiber coupler at the front the light
Tungsten
Halogen Bulb
Collimating
Lens
Fiber Patch Cable
Focusing
Lens
Light Source Main Body
Removable
Fiber Coupler

Compact Stabilized Light Sources Chapter 3: Product Overview
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source main body. With the fiber coupler (focusing lens) removed, users can get
access to the roughly collimated beam after the 1st lens.
The SLS201L/SLS202L features a quick release mechanism allowing users to
easily remove and put back the fiber coupler, switching between a free space light
source and a fiber coupled one.
3.5. Optional Collimator
Thorlabs also provides optional collimator (not included in the package) for
SLS201L and SLS202L. As shown in Figure 5, the collimator works as an
alternative to the fiber coupler. It utilize the same focusing lens as in the fiber
coupler to focus the roughly collimated beam from the 1st lens inside the light
source main body into a 1mm pinhole. The pinhole clean up the beam and then
the beam is collimated again through a 3rd lens, giving a much better collimated
free space beam output.
Figure 5 Optional Collimator of SLS201L/SLS202L
Tungsten
Halogen Bulb
Light Source Main Body
Collimating Lens
Collimating
Lens
Focusing
Lens
Pinhole
Optional Collimator

Compact Stabilized Light Sources Chapter 3: Product Overview
Rev F, October 14, 2021 Page 7
3.6. Output Stabilization
Unlike traditional filament based light sources, the SLS201L/SLS202L will not
suffer either from a gradual decrease or short term fluctuation in brightness during
its lifetime.
SLS201L/SLS202L light source is equipped with an internal feedback loop and
therefore can ensure a constant intensity, low noise and long life span. The
principle of operation is depicted in the block diagram below. The optical intensity
is measured by an internal photodiode, which feeds its monitor signal to the
controller unit. The controller unit then adjusts the driving current of the power
supply to compensate any drift or fluctuation in the optical output.
Figure 6 Closed Feedback Loop in SLS201L/SLS202L

Compact Stabilized Light Sources Chapter 4: Operation
Page 8 CTN002682-D02
Chapter 4 Operation
4.1. Part List
The package contains the following items:
1. SLS201L/SLS202L Light Source
2. DS12 12 V Power Supply
3. Power Cord
4. 1.3 mm (0.050") Hex Key
5. 1.5 mm Hex Key
6. 2 mm (5/64") Hex Key
7. 400µm core, 0.39NA Fiber Patch Cable (SLS201L only)
8. 30 mm Hex Wrench
4.2. Setting Up on a Working Surface
The light source has four non-adjustable plastic feet at the bottom so that it can be
placed directly onto a flat working surfaces, as shown in Figure 7 (a). It also has
two 1/4"-20 (M6) threaded mounting hole on the bottom, which are compatible with
Thorlabs standard optical posts and post holders, enabling it to be mounted on a
breadboard or optical as shown in Figure 7 (b).
(a) (b)
Figure 7 SLS201L Set Up on a Working Surface

Compact Stabilized Light Sources Chapter 4: Operation
Rev F, October 14, 2021 Page 9
4.3. Switching on the Light Source
After setting up the light source on a working surface, follow the steps below:
Figure 8 Switching on SLS201L/SLS202L
1. Connect the power supply to the 4-pin "Power In" plug on the back panel
of the light source;
2. Rotate the threaded cap on the connector to lock it;
3. Flip the toggle switch to "I" to turn on the light source.
During normal operation, the green LED on the back panel will be lit. Please allow
45 minutes warm-up time for the light source to reach a stable state. Please notice
that the cooling fan on the back panel works will only rotate after the interior of the
light source reaches 65 °C. It is completely normal for the fan not to rotate during
operations.
CAUTION: HOT SURFACE
The housing of the light source can get very hot during operation. The
temperature may reach ~60 °C. Avoid extensive contact with skin.
WARNING
The light source generates high power IR output. Do NOT look directly at the
light source beam during operation. Do NOT place hand or body part in the light
beam as this may cause burning.

Compact Stabilized Light Sources Chapter 4: Operation
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4.4. Filter Holder
The light source is equipped with a removable filter holder. The filter holder (filters
sold separately) has an SM1 internal thread and one retaining ring. It allows the
user to mount any Ø25 mm or Ø1" optics, the thickness of which is less than 8 mm,
inside the light source.
The removable filter can be locked into place with the filter setscrew, located on
the side of the stabilized light source. Use included 1.5 mm hex key to
tighten/loosen the setscrew.
Figure 9 Removable Filter Holder of SLS201L
4.5. Front Fiber Coupler
The light source also features a fiber coupler at the output of the device. The fiber
coupler has standard SMA connector for easy connection with SMA fiber patch
cables. The fiber adapter is pre-adjusted to its optimum position before shipping
out and does not require users to re-align in most circumstances.
The SLS201L/SLS202L features a quick release mechanism allowing users to
easily install and remove the fiber coupler, switching between a free space light
source and a fiber coupled one. The great mechanical repeatability of the quick
release mechanism ensures that installing/removing the fiber coupler will not
change its positioning relative to the bulb, thus ensuring a constant output power
level.
Figure 10 Removable Front Lens Tube of SLS201L
Filter lock
Lock

Compact Stabilized Light Sources Chapter 4: Operation
Rev F, October 14, 2021 Page 11
As shown in Figure 10, the fiber coupler is installed onto the light source main body
with a quick release blade mechanism and secured by a set screw. For free space
applications, loosen the set screw with the included 0.050" (1.3 mm) hex key and
turn the fiber coupler counterclockwise to unlock and remove the fiber coupler
After remove the fiber coupler, users can see the collimating lens in the light source
and get access to a roughly collimated beam.
The SLS201L light source is shipped with a 1 m long, SMA to SMA fiber patch
cable with below specs:
Core
Diameter
NA
Cladding
Diameter
Jacket
Bend Radius
Wavelength
Range
Short Term
Long Term
400
± 8 µm
0.39
± 0.02
425
± 10 µm
FT030
(Ø3 mm)
20 mm
40 mm
400 to 2200 nm
(Low OH)
The SLS202L light source does not include any fiber patch cable, it is
recommended to use with fluoride fibers which are also available on Thorlabs
website: www.thorlabs.com
4.6. Adjusting Fiber Coupler Position
The fiber adapter is pre-adjusted to its optimum position before shipping out. But
if really necessary, it is also allow users to do adjustment. As shown in below
Figure 11, use the included 30 mm hex wrench to loosen the external retaining
ring by turning it counterclockwise. Then rotate the SMA fiber adapter to adjust its
position.
Figure 11 Adjust Fiber Adapter Position
4.7. Collimating Accessory (Optional)
Thorlabs also offer collimators for SLS201L and SLSL202L separately as optional
accessories for the light source. They are available on Thorlabs website:
www.thorlabs.com
Loosen Locking Ring
Rotate the Fiber Adapter
for Position Adjustment

Compact Stabilized Light Sources Chapter 4: Operation
Page 12 CTN002682-D02
The collimator provides a well collimated beam but with a reduced power level. It
also features the same quick release mechanism as in the standard fiber coupler,
allowing quick and easy swap between the two different types of accessories.
Figure 12 Collimator Installed on SLS201L
4.8. Application Ideas
There are four 4-40 threaded holes on the front panel of the light source house to
allow the integration of Thorlabs’ 30 mm Cage System. The SM1 internal thread in
the front lens tube also provides compatibility with Thorlabs’ SM1 Lens Tubes and
optical mounts.
Figure 13 illustrates how an SLS201L/SLS202L light source can be integrated with
a 30 mm cage system and SM1 lens tube.
Figure 13 SLS201L/SLS202L with 30 mm Cage System and SM1 Lens Tube

Compact Stabilized Light Sources Chapter 4: Operation
Rev F, October 14, 2021 Page 13
4.9. Bulb Module Replacement
Warning
Always power off the unit before opening the housing.
Warning
The bulb surface temperature may reach a few hundred °C during operation.
Always wait at least 10 minutes after turning off the lamp for cool down before
performing a bulb module replacement.
Caution
Wear protective gloves when handling the bulb module. Moisture and grease
from hands left on the bulb may shorten the bulb lifetime.
Warning
The electronics inside a light source are ESD sensitive. When performing a bulb
module replacement, always wear ESD protection to avoid damaging the light
source.
Thorlabs offers pre-aligned bulb replacement modules for SLS201L and SLS202L
light source. The replacement modules are available on www.thorlabs.com under
the SLS251 and SLS252 item numbers, respectively.
To replace the bulb module, place the light source upside down to reveal the
underside of the unit. Using the included 5/64" (2 mm) hex key, remove the screw
closest to the end of the unit from both the left and right sides. DO NOT remove
the screws closest to the fan ventilation holes.
Figure 14 Remove the two screws at the rear of the light source.
Using the same 2 mm hex key, remove the four screws holding on the cavity cover.
Remove
(Both
Sides)
DO NOT Remove

Compact Stabilized Light Sources Chapter 4: Operation
Page 14 CTN002682-D02
Figure 15 Remove the four screws holding the cover.
Then using the 1.5 mm hex key included with the replacement bulb, remove the
cap screw that locks the bulb module.
Figure 16 Loosen the bulb module locking screw.
Unplug the white plug that is connected to the bulb module. (It is located on the far
side of the circuit board if the output aperture of the lamp is facing to the right.)
Figure 17 Unplug the bulb module connector.
Carefully pull out the old module by sliding the wire and attached plug out. Watch
out for the PD signal wires when pulling out the old module since they may get in
the way.
Figure 18 Pull out the bulb module.
Unplug

Compact Stabilized Light Sources Chapter 4: Operation
Rev F, October 14, 2021 Page 15
Two aluminum dowel pins, located on either side of the bulb module, may slip out
of their holes while the module is being removed. Be careful not to misplace them
as they are needed for the new module installation.
Figure 19 Do not remove the dowel pins on the bulb module.
To install the new bulb module, place the two dowel pins in their corresponding
holes in the new bulb module.
Slide the new bulb module in the bulb chamber. Pass the wire and plug through
the hole in the central wall first and then insert the module. The two dowel pins
should slide smoothly into the holes in the wall.
While pressing the bulb against the central wall, screw the cap screw back in using
the included 1.5 mm hex key.
Insert the white plug back into the circuit board and secure the cavity cover.
Figure 20 Holes on the Central Wall for Bulb Dowel Pins

Compact Stabilized Light Sources Chapter 5: Specifications
Page 16 CTN002682-D02
Chapter 5 Specifications
Specifications SLS201L(/M) SLS202L(/M)
Wavelength Range
360 – 2600 nm
450 – 5500 nm
Peak Wavelength
1
1000 nm
1500 nm
Color Temperature
2796 K
1900 K
Color Temperature Stability
±15 K
Bulb Power
9 W
7.2 W
Fiber Coupled Output Power (Typical)
10 mW
2
1.5 mW
3
Free Space Output Power
(Typical)
4
500 mW
700 mW
Collimated Output Power (Typical)5
60 mW
15 mW
Beam Divergence without Fiber Coupler
6
8.2°
13.8°
Collimated Beam Divergence5,6
2°
1.4°
Collimated Beam Diameter
5,7
24 mm
10 mm
Output Power Drift per Hour (Typical)
0.01%
Optical Power Drift per °C (Typical)
0.1%
Output Power Stability
8
< 0.05%
Power Supply
100 – 240 VAC
Operating Temperature
0 to 45 °C
Storage Temperature
-15 to 70 °C
Dimension
(L x W x H)
216.4 mm × 55.0 mm x 57.5 mm
(8.52" × 2.17" × 2.26")
1Theoretic Value based on Black Body Radiation.
2Measured with Included fiber patch cable at beginning of bulb lifetime.
3Measured with Thorlabs MZ41L1 ZrF4MIR patch cable at the beginning of bulb lifetime.
4Measured at the output port of the light source with fiber coupler removed.
5Measured with optional collimator accessory.
6Half Angle, Design Value @ 587 nm
7Measured 10 cm away from the collimating lens.
8Standard deviation of optical power value in percentage, measured at room temperature
over a 1 hour period with 1 Hz sampling rate after 45 minutes warm-up.

Compact Stabilized Light Sources Chapter 6: Mechanical Drawing
Rev F, October 14, 2021 Page 17
Chapter 6 Mechanical Drawing