Optical Reference Cavity

MENLO Ultrastable Laser Systems ORC Cavities 3w


Advanced Features and Benefits

  • Ultrastable optical reference for laser frequency stabilization
  • Compact footprint
  • 6U rack-mountable option (ORC-Cubic)
  • Highly customizable – entire portfolio available as building blocks
  ORC-Cubic ORC-Cylindric

500–2000 nm (IBS coatings)

900–5000 nm (XTAL coatings)

500–2000 nm (IBS coatings)

900–5000 nm (XTAL coatings)

Finesse low / mid / high low / mid / high
Cavity Length 5 cm 12.1 cm
Free Spectral Range 3 GHz 1.24 GHz
Windows AR coated, angled and wedged AR coated, angled and wedged
Thermal Shields active and passive active
Linear Drift Rate ~150 mHz/s ~150 mHz/s
Ambient Temperature Sensitivity ~4 mK/°C ~4 mK/°C
Temperature Sensor 10 kΩ NTC 10 kΩ NTC
Peltier Elements 2x 25 W 1x 56 W
Ion Getter Pump 5 l/s 10 l/s
Achievable Pressure < 10-7 mbar < 10-7 mbar
Stainless Steel Valve Cu sealed, KF flange Cu sealed, CF flange
Dimensions W 28 cm, L 28 cm, H 18 cm W 48 cm, L 35 cm, H 35 cm
Vacuum Chamber Material aluminum stainless steel
Mass 15 kg 55 kg
Rack Integration 19”, 6U enclosure (optional)  n.a.


The Optical Reference Cavity (ORC) series is our solution when customization is pivotal. Choose from the exceptional portfolio of adaptations, auxiliary instruments and services and profit from our experience in designing generations of ultrastable laser systems.

The ORC family are Fabry-Pérot-type cavities with a resonator spacer made out of ultra-low expansion glass (ULE). The cavity is mounted in a sealed vacuum housing, engineered for exceptional temperature stability to enable low frequency drift. The compact design ensures minimal spatial demand. The ORC-Cubic is available as a 6U, 19” rack module. It is based on a rigidly mounted cubic spacer licensed from National Physical Laboratory. The ORC-Cylindric uses a cylindric spacer designed by the Physikalisch Technische Bundesanstalt, that is horizontally mounted on four support points. Here, portability is ensured by a mechanical locking mechanism.

A broad variety of add-ons and options is available for customization: mirror substrates are available as ULE or fused silica (FS), mirror coatings can either be ion-beam sputtered (IBS) or crystalline (XTAL), the latter is needed when ultimately low thermal noise is paramount. The highly reflective coatings are available over a broad wavelength range and also as dual or triple highly reflective mirrors. Modules for input coupling, PDH locking, and output monitoring can be rigidly mounted onto the chamber, rendering tedious realignments after transportation obsolete.

Every system is baked-out during the assembly process. The built-in NTC and Peltier elements are accessible via vacuum feedthroughs, allowing for operation at the zero crossing of the coefficient of thermal expansion (CTE). Characterization of the CTE is available on request. Both cavities are also available without enclosure.

Reference Cavity Spacers:

MENLO Ultrastable Laser Systems ORC Cavity Spacer 3w


  • Optics Module for Input Coupling, PDH Locking, and Monitoring


    Two modules holding all optics required for input coupling to the cavity, Pound-Drever-Hall locking as well as mode and power monitoring of the transmitted light. The modules are rigidly mounted onto the vacuum housing making realignments after transportation obsolete.

  • ORC Fused Silica Mirror Substrate Package

    Product Code: ORC-FS-IBS

    The Fused Silica Mirror Substrate Package is an economic solution to reduce the thermal noise floor of the cavity. Here, fused silica mirror substrates are used instead of ULE substrates.  In order to be able to operate the cavity at room temperature, ULE compensation rings (patented design, sold under a licensing agreement with the Physikalisch Technische Bundesanstalt (PTB)) are contacted onto the fused silica substrates.

  • ORC Crystalline Mirror Coating Package

    Product Code: ORC-FS-XTAL

    For ultimate frequency stability, the ORC-FS-XTAL Option is indispensable. This option is available for the ORC-Cubic only. Here, highly reflective crystalline coatings are used on fused silica substrates as cavity mirrors. This strongly reduces the thermal noise floor. In order to be able to operate the cavity at room temperature, ULE compensation rings (patented design sold under PTB license) are contacted onto the fused silica substrates.

  • Rack Mounting Package

    Product Code: ORC-CUB-6U

    Using the Rack Mounting Package, the ORC can be easily mounted in a standard 19-inch rack with 6 height units. This option is available for the ORC-Cubic only. For rounding off the compact rack solution, we recommend using this option together with the optics modules for input coupling, PDH locking and monitoring.

  • ORC Mirror Coatings for Multiple Wavelengths Package

    Product Code: ORC-MWL

    For simultaneous stabilization of multiple lasers to the same reference cavity, we provide customized cavity mirrors. These custom coatings are highly reflective in two or multiple wavelength ranges.

  • Pound-Drever-Hall Servo Electronics Package

    Product Code: ORC-PDH

    For stabilizing the laser to the cavity, this package provides all required electronics in a single configurable device, i.e., Menlo’s SYNCRO controller (3rd generation). The SYNCRO provides full software control of all parameters and intuitive use via touchscreen. This 3U, 19-inch device can also be remotely accessed via LAN. The package includes phase modulation and demodulation, and a fast analog PI²D controller (>10 MHz bandwidth) providing two servo outputs for fast and slow actuators.

  • Characterization of the Zero-Crossing Temperature

    Product Code: ORC-CTE

    It is of ultimate importance to determine the zero-crossing temperature of the coefficient of thermal expansion (CTE) of the ULE reference cavity. This procedure, that is in principle simple, requires a dedicated measurement infrastructure and is very time consuming due to the long thermalization time constant. Menlo routinely characterizes the CTE zero-crossing to within 50 mK.

  • TEC Driver Package

    Product Code: ORC-TEC

    A TEC driver to stabilize the temperature of the reference cavity to the zero-crossing temperature of the coefficient of thermal expansion.

  • Reference Cavity without Vacuum Enclosure

    Product Code: ORC-CAV-CUB / ORC-CAV-CYL

    Reference cavity with optically contacted high finesse cavity mirrors but without vacuum enclosure and ion getter pump. Custom cavity designs are also available upon request.

  • Reference Cavity Spacer Package

    Product Code: ORC-SPCR-CUB, ORC-SPCR-CYL

    Bare cavity spacer made out of ULE glass without cavity mirrors to build your own reference cavity.  CAD models are available for cylindric and cubic geometries.

Calculated thermal noise floor:


    mirror substrates – mirror coatings 
Thermal noise ADEV limit
5 cm CUBIC
1.4 x 10-15 9 x 10-16 4 x 10-16
Thermal noise ADEV limit
5.8 x 10-16 3.8 x 10-16 1.6 x 10-16


Fractional frequency instability of the ORC integrated in Menlo Systems' ORS ultrastable laser system:


modallan ORS v2 20190129


PN ProfKatoriCavities v3 20190129 2

Note: The cavity performance data shown above is guaranteed only for the ORC integrated in a Menlo Systems' ORS ultrastable laser system.

Menlo Expert Ben Sprenger 2019
Dr. Benjamin Sprenger
Your direct line to our expert

Data sheets

Product literature

Ordering information

  • Product Code
  • ORC-Cylindric
  • ORC-Cubic

+49 89 189166 0

Menlo Systems, Inc.
+1 973 300 4490

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