THORLABS LCC3111H User manual

Liquid Crystal Noise Eaters
User Guide

Liquid Crystal Noise Eater
Page 1 Rev C, Dec 8, 2015
Table of Contents
Chapter 1Warning Symbol Definitions ...........................................2
Chapter 2Safety.................................................................................3
Chapter 3Product Overview.............................................................4
Chapter 4Setup..................................................................................5
4.1.MountingandAlignment...............................................5
4.2.PowerSupply.................................................................6
4.3.PoweringONtheNoiseEater.........................................6
4.4.BeamCentering.............................................................6
Chapter 5Operation...........................................................................7
5.1.SelectingthePowerRange............................................7
5.2.ModulatetheOutputPower........................................10
5.3.SettingtheOutputPowerLevel...................................10
5.3.1.Maximizing the Output Power Using an External Measurement
Device........................................................................................11
5.3.2.Maximizing the Output Power Using the Indicator LED.............12
Chapter 6Specifications.................................................................13
Chapter 7Mechanical Drawing.......................................................15
Chapter 8Maintenance....................................................................16
8.1.Troubleshooting..........................................................16
Chapter 9Regulatory.......................................................................17
9.1.WasteTreatmentisYourOwnResponsibility...............17
9.2.EcologicalBackground.................................................17
Chapter 10Thorlabs Worldwide Contacts.......................................18

Liquid Crystal Noise Eater 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
Caution: Spinning Blades May Cause Harm

Liquid Crystal Noise Eater
Page 3 Rev C, Dec 8, 2015
Chapter 2 Safety
Do Not Open Housing!
The Noise Eater has no user-serviceable parts. Service should only be
performed by trained service personnel.
All statements regarding safety of operation and technical data in this instruction
manual will only apply when the unit is operated correctly.
WARNING
Laser Radiation – Avoid Exposure to Beam

Liquid Crystal Noise Eater Chapter 3: Product Overview
Page 4
Chapter 3 Product Overview
Thorlabs’ Liquid Crystal Noise Eaters are precision instruments for stabilizing and
attenuating laser power. The noise eater consists of a variable attenuator (liquid
crystal wave plate and polarizer), a calibrated beam splitter, and a servo
controller to control the modulator, as depicted in the block diagram below.
Figure 1 Noise Eater Block Diagram
Linearly polarized light is input into the liquid crystal retarder, which, together with
the output polarizer, acts as a variable retarder. A beamsplitter then sends a
small part of the beam to a feedback loop consisting of a photodiode and control
servo. The servo compares the optical signal to a preset signal level and applies
the appropriate adjustment voltage until the optical signal reaches the desired
level.
The noise eater can also be used as a variable attenuator even without the
presence of noise. By adjusting the resistance of the potentiometer, the user can
set the desired output power level.

Liquid Crystal Noise Eater
Page 5 Rev C, Dec 8, 2015
Chapter 4 Setup
4.1. Mounting and Alignment
The noise eater is designed to work with linearly polarized input light aligned with
the direction of the arrow near the input aperture. Linearly polarized light and
proper alignment of the direction of polarization are important for achieving the
best results from the noise eater.
In order to minimize optical losses, the noise eater does not have an input
polarizer. If the incident light is not linearly polarized, a linear polarizer (such as
our LPVIS or LPNIR polarizers) should be used before the noise eater.
If the incident light is linearly polarized but is not aligned exactly vertically or
horizontally, a half-wave plate can be used before the noise eater to rotate the
polarization axis. As shown in the photo below, the noise eater’s cage mount can
be used along with a CRM1 cage rotation mount to rotate the half-wave plate,
thus aligning the polarization axis with the noise eater.
Figure 2 CRM1 Cage Rotation Mount holding a Mounted Half-Wave Plate
(such as the WPH10M-633), secured to the LCC3111H Noise Eater with ER
Cage Rods
For post mounting, the noise eater is equipped with two 8-32 (M4) threaded
holes. These holes are offset by 90°, so that light with a vertical or horizontal
polarization axis can be aligned with the noise eater. The four 4-40 holes on the
front of the noise eater can also be used to mount the noise eater in either a
horizontal or vertical orientation using the Thorlabs Cage System

Liquid Crystal Noise Eater Chapter 4: Setup
Page 6
Figure 3 Horizontally and Vertically Mounted LCC3111H Noise Eaters. Note
the direction of the input polarization indicated by the double arrow.
4.2. Power Supply
The noise eater operates with 12 V DC power. We recommend using the AC/DC
power supply that is included with the noise eater for best performance.
4.3. Powering ON the Noise Eater
When the noise eater is connected to the power supply, it automatically powers
on. There is no additional power switch.
4.4. Beam Centering
For best performance of the noise eater, it is recommended that the beam is well
centered in the input aperture. Due to the optical path inside the noise eater, the
output beam will be shifted down by 1.0 mm if the noise eater is mounted
vertically as shown in Figure 3 (right). Similarly, the output beam will be shifted
sideways by 1.0 mm if the noise eater is mounted horizontally as in Figure 3
(left).

Liquid Crystal Noise Eater
Page 7 Rev C, Dec 8, 2015
Chapter 5 Operation
5.1. Selecting the Power Range
The LCC3112H and LCC3113H have two selection switches at the top of the
case which are used to select the input power range. When the high/low power
switch is set to “LOW”, the input power range can be set from 1 mW to 30 mW,
and when the status switch set to “HIGH”, the input power range can be set from
100 mW to 500. The LCC3111H and LCC3111L have only one selection switch
which can set the input power range from 1 mW to 30 mW or 100 mW to 500
mW. The power selector should be set to the lowest value that is still higher than
the actual power of the laser. For example, if the LCC3111L is being used with a
beam power of 8 mW at 635 nm, the selector should be set to 10 mW.
Figure 4 Top View of the LCC3111L (Left), LCC3111H (Center) and
LCC3112H/LCC3113H (Right) Noise Eaters
The LCC3111H and LCC3112H noise eaters use a Silicon detector, while the
LCC3113H uses a Germanium detector, as part of the feedback loop. The
responsivity of the detector is different for different wavelengths, and so the
power settings on the selector only correspond to the design wavelength of the
detector (635 nm for LCC3111H and LCC3111L, 780 nm for LCC3112H, 1550
nm for LCC3113H). The power range at a given wavelength is inversely
proportional to the responsivity (higher responsivity value will result lower power
range value). The graph below shows the relative responsivity of both detectors
at a range of wavelengths. The tables below show a rough estimate of the power
settings at various wavelengths for each model.

Liquid Crystal Noise Eater Chapter 5: Operation
Page 8
Figure 5 Noise Eaters Normalized Responsivity
5.2. Max Powers at Various Wavelengths
The tables below list the maximum input powers for each noise eater, specified
for a variety of input wavelengths and switch settings. Please note that these
maximum power levels correspond to the feedback electronics of the noise eater,
and in some cases, the actual maximum input power is instead limited by the
damage threshold of the noise eater. For the high power noise eaters
(LCC3111H, LCC3112H, and LCC3113H), this damage threshold is 8 W/cm2,
which corresponds to a maximum input power of 1 W if the input power is
distributed evenly across the Ø4 mm clear aperture. For the low power noise
eaters (LCC3111L, LCC3111, LCC3112, and LCC3113), the damage threshold
is 0.8 W/cm2, which corresponds to a maximum input power of 100 mW if the
input power is again distributed evenly across the Ø4 mm clear aperture.

Liquid Crystal Noise Eater
Page 9 Rev C, Dec 8, 2015
LCC3111H Max Input Power at Various Wavelengths
Switch
Status Power Level at 450 nm Power Level at 550 nm Power Level at 635 nm
100 mW 200 mW 150 mW 100 mW
300 mW 600 mWa450 mW 300 mW
500 mW 1000 mWa750 mWa500 mW
LCC3111L Max Input Power at Various Wavelengths
Switch
Status Power Level at 450 nm Power Level at 550 nm Power Level at 635 nm
1 mW 2 mW 1.5 mW 1 mW
3 mW 6 mW 4.5 mW 3 mW
5 mW 20 mW 15 mW 10 mW
30 mW 60 mW 45 mW 30 mW
LCC3112H Power Ranges at Various Wavelengths
Switch
Status
Power
Level at
650 nm
Power
Level at
700 nm
Power
Level at
780 nm
Power
Level at
900 nm
Power
Level at
1000 nm
Power Level
at 1100 nm
Low A 1.2 mw 1.1 mW 1 mW 0.9 mW 0.9 mW 3.3 mW
Low B 3.5 mW 3.3 mW 3 mW 2.6 mW 2.7 mW 10.0 mW
Low C 11.8 mW 11.1 mW 10 mW 8.8 mW 8.9 mW 33.3 mW
Low D 35.5 mW 33.3 mW 30 mW 26.3 mW 26.8 mW 100.0 mW
High A 120.0 mW 111.0 mW 100 mW 86.0 mW 89.3 mW 333 mW
High B 355.5 mW 333.0 mW 300 mW 258.0 mW 268 mW 999 mWa
High C 600.0 mWa500 mW 500 mW 430.0 mW 446.6mW 1650 mWa
LCC3113H Power Ranges at Various Wavelengths
Switch
Status
Power
Level at
1050 nm
Power
Level at
1150 nm
Power
Level at
1250 nm
Power
Level at
1350 nm
Power
Level at
1450 nm
Power
Level at
1550 nm
Power
Level at
1620 nm
Low A 1.9 mW 1.6 mW 1.4 mW 1.2 mW 1.0 mW 1 mW 1.6 mW
Low B 5.8 mW 4.8 mW 4.1 mW 3.5 mW 3.1 mW 3 mW 4.8 mW
Low C 19.2 mW 16.0 mW 13.7 mW 11.7 mW 10.4 mW 10 mW 16 mW
Low D 57.6 mW 48.0 mW 41.1 mW 35.1 mW 31.3 mW 30 mW 48 mW
High A 190 mW 160 mW 137 mW 117 mW 104.7 mW 100 mW 160 mW
High B 500 mW 480 mW 411 mW 351 mW 313.4 mW 300 mW 480 mW
High C 835 mWa800 mWa685 mWa585 mWa520 mWa500 mW 800 mWa
a. The maximum power levels specified here are for the feedback electronics, but the maximum
input power at these settings is limited by the damage threshold of the liquid crystal retarder,
which is 8 W/cm2. See the section 5.2, Max Powers at Various Wavelengths, for details.