THORLABS XM-ORC Series User manual

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User Manual
Optical Reference Cavity with
Crystalline Mirrors
XM-ORC Series
Important Document
Please keep for your records

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Precision in Photonics. Together, we shape light.
Menlo Systems, a leading developer and global supplier of instrumentation for
high-precision metrology, was founded in 2001 as a spin-off of the Max-Planck-
Institute of Quantum Optics. Known for the Nobel-Prize-winning Optical Frequency
Comb technology, the Munich based company offers complete solutions based on
ultrafast lasers, synchronization electronics and THz systems for applications in
industry and research.
Thorlabs, a vertically integrated photonics products manufacturer, was founded in
1989 to serve the laser and electro-optics research market. As that market has
spawned a multitude of technical innovations, Thorlabs has extended its core
competencies in an effort to play an ever-increasing role to serve the Photonics
Industry at the research end, as well as the industrial, life science, medical, and
defense segments. The organization’s highly integrated and diverse manufacturing
assets include semiconductor fabrication of Fabry-Perot, DFB, and VCSEL lasers;
fiber towers for drawing both silica and fluoride glass optical fibers; MBE/MOCVD
epitaxial wafer growth reactors; extensive glass and metal fabrication facilities;
advanced thin film deposition capabilities; and optomechanical and optoelectronic
shops.

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I. IMPRINT
Title: User Manual –Optical Reference Cavity with Crystalline Mirrors –XM-ORC
Manufacturer: Menlo Systems GmbH, Munich, Germany
Thorlabs Inc., Newton, New Jersey, USA
Copyright: © 2023 Menlo Systems GmbH. All rights reserved.
Reproduction by any means of any image in this user manual is prohibited without
the prior consent of Menlo Systems GmbH.
All product designations used in this manual are registered trademarks of the
respective companies.
Changes: Subject to technical changes without prior notice.

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II. TABLE OF CONTENTS
I. IMPRINT................................................................................................................................................ 4
II. TABLE OF CONTENTS ............................................................................................................................ 5
III. SAFETY INSTRUCTIONS ......................................................................................................................... 7
III.1 Laser Safety................................................................................................................................. 7
Intended Use of the Laser..................................................................................................... 7
Laser Hazard Classification.................................................................................................... 7
Laser Safety Precautions ....................................................................................................... 8
Protective Eyewear ............................................................................................................... 9
Safety Features of Your Laser................................................................................................ 9
III.2 Electrical Safety Precautions..................................................................................................... 11
1. Principle of Operation......................................................................................................................... 13
2. System Description............................................................................................................................. 14
Ion Getter Pump Controller....................................................................................................... 14
Vacuum Chamber ...................................................................................................................... 15
Optically Contacted Cavity......................................................................................................... 15
Temperature Stabilization ......................................................................................................... 16
3. Setting Up the XM-ORC ...................................................................................................................... 18
Unpacking and establishing Vacuum......................................................................................... 18
4. Warranty............................................................................................................................................. 20
Restrictions of Warranty............................................................................................................ 20
A. Customer Service................................................................................................................................ 21
A.1 Factory Service & Repair........................................................................................................... 21
A.2 Additional Service Plan............................................................................................................. 21
B. Regulatory........................................................................................................................................... 22
B.1 Waste Treatment is Your Own Responsibility........................................................................... 22
B.2 Ecological Background............................................................................................................... 22
C. Contacts.............................................................................................................................................. 23

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III. SAFETY INSTRUCTIONS
Please follow the directions given in this manual; otherwise the safety level the laser has been
designed to provide might be affected.
III.1 LASER SAFETY
INTENDED USE OF THE LASER
Your laser is a versatile light source for research and industry applications. The laser is designed
for indoor use only (IP21, NEMA Type 1). It is not designed for use as a medical device or as a part
of a medical device.
LASER HAZARD CLASSIFICATION
Lasers and laser systems are classified according to EN 60825-1:2014.
The XM-ORC may be coupled to a laser source classified as 3B. When in proper condition, i.e. all
housing components are in place, all laser connection points should be equipped with optical
fibers or closed with the caps, so there is no leakage radiation to the outside, the system equals
laser class 1 conditions.
A laser classification is based on several factors including wavelength of emission, power output,
accessible emission level, and emission duration.
CLASSIFICATION OF THE LASER MODEL
Please, carefully read the section below that corresponds to the class of your laser.
POTENTIAL HAZARDS ASSOCIATED WITH CLASS 1M LASERS
A Class 1M laser is safe for all conditions of use except when passed through magnifying optics
such as microscopes and telescopes, or re-focusing optics such as a lens. Class 1M lasers produce
large-diameter beams, or beams that are divergent.
Do not use microscopes or other re-focusing optics with the system when active.
POTENTIAL HAZARDS ASSOCIATED WITH CLASS 3B LASERS
A Class 3B laser can be hazardous if the eye is exposed directly. This includes intra-beam viewing
or specular reflections. Exposition of the eye to diffuse reflections typically does not present a
hazard. Class 3B lasers with higher output power can burn skin and ignite combustible material
when the beam diameter is small or when the beam is focused. Protective eyewear is
imperatively required when working with Class 3B lasers.

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LASER SAFETY PRECAUTIONS
The laser system may constitute a serious potential threat for eye injury
resulting from intrabeam viewing. It generally does not represent a
diffuse reflection hazard, and therefore only minor potential skin or a
fire hazards.
▪Areas where a laser with accessible radiation is operated should be marked with
warning symbols according to local regulations
▪Operate the laser only in a well-controlled area, for example within a closed room with
covered or filtered windows and controlled access
▪The plane the laser is guided within should be closed off to all sides by protective
screens
▪Do not remove the cover or any sidewall of the system enclosure
▪The laser beam should be guided such that the beam is confined to a horizontal plane.
The horizontal plane the beam is guided within must be above or below eye level for
either sitting or standing positions
▪Mount the system on a firm support to assure that the laser beam never deviates
accidently from the intended path
▪Assure that individuals who operate the laser are trained in laser safety and authorized
to operate a laser
▪Persons using lasers should be informed about safety measures according to local
regulations
▪Only experienced personnel should operate the laser and never leave an operable
laser unattended if there is a chance that an unauthorized user may attempt to operate
it. A key switch must be used if untrained persons may gain access to the laser. A
warning light or buzzer must be used to indicate that the laser is in operation
▪Optical fibers should only be modified, plugged in or removed when the system is
deactivated or the individual devices (transmitter and receiver) are secured and
switched off. Terminate all beam paths at the end of their useful path. Always attach
end caps to unplugged connectors.
▪Persons working with laser radiation should remove wristwatches, rings and other
items that could reflect laser radiation before starting to work
▪Make sure that the surfaces of tools that are used to work on an optical setup do not
produce specular reflections

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▪Eliminate unnecessary specular (mirror-like) surfaces from the vicinity of the laser
beam path, or avoid aiming at such surfaces
▪Avoid looking with the unprotected eye along or near the beam axis. Some alignment
procedures may place personnel at risk by requiring close proximity to the beam where
the chance of hazardous specular reflections is the greatest
▪Assure that any spectators are not potentially exposed to hazardous conditions
▪Never aim the laser beam at anyone else’s eyes
▪Follow standard maintenance procedures. If you have any further questions, please
contact Menlo Systems Customer Service
▪Assure that individuals do not look directly into a laser beam with optical instruments
unless an adequate protective filter is present within the optical train
▪Users need to wear appropriate eye protection when operating Class 3R, 3B or Class 4
lasers
▪Use proper laser safety eyewear if there is a chance that the eye will be exposed to the
beam or a hazardous specular reflection
▪Terminate all beams at the end of their useful paths
▪Use low power settings, beam shutters and laser output filters to reduce the beam
power to less hazardous levels when the full output power is not required
PROTECTIVE EYEWEAR
The calculation for protective eyewear can be done according to the European standard EN 207.
When your laser model is exclusively equipped with fiber output ports, the given safety ratings
are based on the assumption of an open fiber end with a divergent laser beam. If the laser beam
is collimated after the fiber, the higher safety ratings might apply.
Commercial laser safety glasses are rated with an L-rating according to EN 207 or with an optical
density (OD) rating according to ANSI Z136.1 or with both.
This is just a recommendation. Every user is responsible to take care for proper eyewear safety.
SAFETY FEATURES OF YOUR LASER
▪Key operated laser controller
▪Optical emission indicator on the laser controller
▪Interlock circuits at Syncro and Vacuum Pump

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▪Light-tight encapsulation of the laser sources and robust individual housings.
▪Protective grounding (electrical class I equipment) and fine fuses on individual units.
▪Operating instructions (this document).

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III.2 ELECTRICAL SAFETY PRECAUTIONS
Part of the system contains hazardous voltage (mains voltage 230V / 240V).
The Ion Pump Power Supply and Ion Pump work with high voltage of 7000V, for
details refer to the separate manuals (900026_Small-pump-Controller-SPCe-
_EN_manual; 900013_ION-Pump_EN_manual).
You should make sure that electrical equipment used for work is safe. Here is a list of actions that
should be taken:
▪Do not use wet hands when turning on electrical equipment
▪Check that the electrical equipment is suitable for the work and way in which it is going
to be used
▪Check that the electrical equipment is in good condition
▪Check that the equipment is suitable for the electrical supply with which it is going to
be used, and the electrical supply is safe
▪Make sure that the user of the equipment is trained to use it safely and can keep others
safe
▪Make sure the user knows which personal protective equipment to wear, how to use
it, and make sure they do so
▪Power failures should be avoided. The ion getter pump must be running continuously.
Before starting the system, make sure that the fuses installed for the
power supply of the system are rated to the correct main supply
voltage. If the supply voltage differs from the value, the already
installed fuses need to be replaced by ones which are appropriately
rated.

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1. PRINCIPLE OF OPERATION
Thank you for choosing our Optical Reference Cavity with Crystalline Mirrors XM-ORC –a high
finesse cavity serving as a reference for a continuous wave (CW) laser. The combination of high
vacuum, temperature stabilization, ultra-low expansion (ULE) glass and high-reflectivity
crystalline (xtal stable™) coated mirrors on fused silica substrates leads to unprecedented
performance in a commercial system.
The Optical Reference Cavity (ORC) is a high finesse Fabry-Pérot cavity, to which a single mode
continuous wave laser can be actively frequency stabilized. The stabilization of the laser
frequency onto a transmission mode of the cavity can be realized through a Pound-Drever-Hall
(PDH) locking scheme. In this scheme, the error signal is generated by phase modulating the laser
light with an electro-optic modulator (EOM) and down-mixing the photodiode signal of the
reflected light from the cavity with the modulation frequency to DC. The frequency of the laser
is then stabilized via fast feedback to the current and slow feedback to the temperature or piezo
actuator of the laser (depending on the laser source).
cw
diode laser
output
EOM
collimator
PD
lockbox Pound-
Drever-Hall
λ/2 λ/2
Faraday
Rotator
Figure 1: The light of a CW laser is sent through a phase modulator operating at 20 MHz to
generate sidebands for the PDH lock. A half-wave plate before a polarizing beam cube is
used to adjust the power incident onto the cavity. A Faraday rotator rotates the transmitted
p-polarized beam by 45° and a half-wave plate is used to optimize the polarization alignment
with the crystalline (xtal stable™) coating. In order to avoid splitting due to birefringence,
the linear polarization should be aligned either perpendicular or parallel to the visible flat
edge of the coating. The light reflected from the cavity is polarization rotated by a further
45° and the s-polarized light is reflected on the polarizing beam cube and detected on a
photodetector. The PDH error signal is fed back to the current and the temperature or piezo
actuator of the laser using a PIID loop filter.
When the laser is tightly locked to the cavity, its fractional frequency stability is dominated by
the length fluctuations of the reference cavity. Therefore, the cavity has to be well isolated from
environmental influences in order to minimize its length change. In order to achieve this, the
cavity is operated under high-vacuum, with active temperature stabilization.

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2. SYSTEM DESCRIPTION
The XM-ORC Series optical reference cavity with crystalline coated (xtal stable™) mirrors comes
supplied with the components and specifications as detailed in Table 2.1.
SPECIFICATIONS
XM-ORC Series
Wavelength1
1550, 1397, 1156 or 1064 nm
Thorlabs Mirror Part Numbers
1064 nm –XM15P8 / XM15R8
1156 nm –XM16P8 / XM16R8
1397 nm –XM23P8 / XM23R8
1550 nm –XM14P8 / XM14R8
Finesse
> 300,000 (1550, 1397 or 1156 nm)
> 200,000 (1064 nm)
Cavity Length (ULE Spacer)
12.1 cm
Cavity Mirrors
Crystalline Coating (xtal stable™) on
Fused Silica Substrate
Free Spectral Range
1.24 GHz
Windows
AR Coated, Angled and Wedged
Thermal Shielding
Active
Thermal Noise ADEV Limit2
1.6 x 10-16
Linear Drift Rate
≈150 mHz/s
Ambient Temperature Sensitivity
≈4 mK/°C
Weight
≈55 kg
Incl. Temperature Controller
Incl. Vacuum Pump and Controller
Table 2.1: XM-ORC standard specifications. 1Non-standard wavelengths > 900 nm available
upon request. 2At 1 s averaging.
ION GETTER PUMP CONTROLLER
The ion getter pump controller is used to operate the ion getter pump (IGP) which maintains the
high-vacuum in the vacuum chamber. The controller and the high voltage (HV) must always be
switched on. The pump has a nominal pump rate of 10 l/s and is preferably operated at a voltage
of 7 kV. For further details, refer to manual of the IGP controller, included in the USB drive
provided with your system.

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VACUUM CHAMBER
The vacuum chamber is made out of stainless steel and CF flange components with small leaking
rates. It is continuously pumped by a 10 l/s IGP. This pumping technology works only up to
maximum pressures of 10-4 mbar, which may cause problems if the pump is accidentally shut
down or a power blackout occurs for a longer time interval. If the pump cannot be started after
such an event due to the chamber pressure being too large, an auxiliary pump has to be
connected via a DN40 flange accessible on the back side of the system. This pump is ideally a
turbo pump stand. See the setup instructions in section 3 for details on how to connect a pump
to the vacuum system.
Figure 2: Vacuum chamber
In daily operation, the vacuum pressure can be read on the display of the pump controller in the
control electronics rack. It should always remain below 10-7 mbar.
OPTICALLY CONTACTED CAVITY
The optically contacted cavity consists of a 12.1 cm long cylindrical spacer built out of ULE glass
and two high finesse mirrors comprising crystalline (xtal stable™) coatings on fused silica
substrates and provided with ULE compensation rings. The light in-coupling mirror is plano-
concave with a radius of curvature of 1 m. The outcoupling mirror is plano-planar.

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Figure 3: Optically contacted cylindrical cavity
The cavity is mounted in the vacuum chamber such that there is a small angle between the
chamber’s viewports and the cavity in order to avoid etalons. There is a 7.4 cm distance between
the mirrors and the viewports on both sides.
TEMPERATURE STABILIZATION
NTC and Peltier elements are built into the system and are accessible via vacuum feedthroughs.
This allows for temperature stabilization at the zero crossing of the coefficient of thermal
expansion (CTE) which will be close to room temperature. The specifications given by the
manufacturer for the Peltier element are shown in Table 2.2.
Property
Value
I max (A)
6.0
U max (V)
17.2
Qc max (W)
56
dT max (K)
72
T max (°C)
170
Table 2.2: Specifications of the Peltier element

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The XM-ORC is provided with a TED200C-SP3 TEC controller to stabilize the cavity to the user set
temperature. A cable is provided comprising 15-pin D-Sub connectors for connection between
the rear of the TED200C-SP3 to the underside of the vacuum chamber (adjacent to the transport
lock).
Note: the TED200C-SP3 is a modified version of the Thorlabs standard TED200C and incorporates
a non-standard integrator time constant.
For full operational instructions of the TED200C-SP3 please refer to the document downloads on
the Thorlabs website (https://www.thorlabs.com/thorproduct.cfm?partnumber=TED200C).
For reference: The wires in the cable connected to the NTC and Peltier elements are color-coded
to identify the useful signals. The color code is given in Figure 4.
Figure 4: Color code for the temperature stabilization cable

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3. SETTING UP THE XM-ORC
UNPACKING AND ESTABLISHING VACUUM
Due to the system weight and form factor, it is recommended to have 2 persons perform the
unpacking and installation procedure.
▪Open the top of the wooden box and lift the system out.
▪Carefully place the system to a destination to evacuate the vacuum chamber.
▪Open the DN40 flange by unscrewing the M6 screws. Use a new copper gasket and
connect the DN40 flange to a turbo pump stand. Tighten the connection with the M6
screws and washers. Use three passes of tightening while increasing the torque from
4 Nm to 6 Nm and then to 8 Nm. Always tighten screws in the order of opposing sides
during each pass.
Figure 5: Vacuum components. Breadboard mounted in-coupling and out-coupling optics
are shown by way of example and are not included with the XM-ORC.
▪Turn on the turbo pump. In this step, the path between the pump and the gate valve
is evacuated to check the connection. Proceed if there is no leak, i.e. if the pressure
continuously goes down and reaches a value < 1x10-5 mbar.

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▪Open the hexagonal screw of the gate valve slowly and carefully, monitoring the effect
on the turbo pump thereby ensuring the chamber does not flood during the process.
Evacuate at least to ≈ 7x10-7 mbar.
▪Connect the IGP to power and to the XM-ORC.
▪Start the IGP by pressing HV for a couple of seconds. If the voltage ramps up to 7 kV,
the pump is working properly. If the voltage comes back down after ramping up, it
means the pressure is not low enough and the chamber should be pumped longer with
the turbo pumping station. Target: ≈ 5x10-7 mbar on the IGP controller.
▪Close the gate valve by rotating the hexagonal screw clockwise and switch off the turbo
pump. Make sure that the valve is properly closed. The valve can be damaged by
excessive torque, however closing it by hand is unlikely to cause damage. Note: The
pressure might increase after the valve is closed, but the IGP should quickly capture
the pressure. When the turbo pump is slowing down, no pressure increase on the IGP
should occur.
▪Unscrew the screws of the DN40 flange and remove the turbo pump stand.
▪Use the blank flange and a DN40 copper gasket to seal the open flange.
▪Disengage the transport lock of the cavity by using the vacuum translation stage (see
Figure 6). Do not use excessive force when activating or deactivating the transport lock
as this could damage the mechanics inside the vacuum chamber.
Figure 6: Cavity transport lock mechanism. a. Locked position, b. Unlocked position. To lock
the mechanism: screw the bottom screw downwards it until a higher resistance is felt, then
do the same with the top screw and secure with the nut. To unlock: unscrew the nut and
the top screw, then screw the bottom screw upwards until a higher resistance is felt. You
can use the scale on the left as a reference.
If the XM-ORC needs to be transported again, even for a short distance, the transport lock should
be engaged before transport and disengaged afterwards.

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4. WARRANTY
The separate warranties provided by Menlo and Thorlabs can be found at
https://www.menlosystems.com/legals/standard-terms-and-conditions/
and
https://www.thorlabs.com/support.cfm?section=7&viewtab=1
respectively.
Menlo Systems and Thorlabs warrant material and production of the goods supplied for a period
of twelve months starting from the date of shipment. During this warranty period Menlo Systems
or Thorlabs will see to defaults by repair or by exchange if these are entitled to warranty. In the
instance a warranty claim is to be made, contact should be first arranged through the original
point-of-sale of the goods.
For warranty repairs or service the unit must be sent back to either Menlo Systems GmbH
(Germany) or Thorlabs Inc. or to a place determined by either Menlo Systems GmbH or Thorlabs
Inc. (the “point of repair”). The customer will carry the shipping costs to the point of repair and
in the case of warranty repairs, Menlo Systems GmbH/Thorlabs Inc. will carry the shipping costs
back to the customer.
If no warranty repair is applicable the customer also has to carry the costs for back shipment.
In case of shipment from outside EU duties, taxes etc. which should arise have to be carried by
the customer.
Menlo Systems GmbH and Thorlabs Inc. warrant the hardware determined by Menlo Systems
GmbH and Thorlabs Inc. for this unit to operate fault-free provided that it is handled according
to our requirements.
RESTRICTIONS OF WARRANTY
The warranty mentioned above does not cover errors and defects being the result of improper
treatment, using software or interface(s) not supplied by us, modification, misuse or operation
outside the defined ambient conditions stated by us or unauthorized maintenance.
Further claims will not be consented to and will not be acknowledged. Menlo Systems GmbH
does explicitly not warrant the usability or the economical use for certain cases of application.
Menlo Systems GmbH reserves the right to change this instruction manual or the technical data
of the described unit at any time.