Quick answer

Match the beam expander to your mainframe first, then to the beam you need. For a Zygo 633 nm MST system, the 24 Inch High Resolution Beam Expander (BEX) is the direct fit because it is built for all resolution 633 nm MST mainframes and includes the frame, covers, and mounts. If you only need to drive an existing HD or DynaFiz turret, the High Resolution Turret Driver Board is the simpler spare-part purchase. Buy the expander only when your aperture and magnification needs justify the larger assembly.

Start with the mainframe, not the magnification number

A beam expander is not a universal accessory. The Zygo 24 Inch High Resolution Beam Expander (BEX) is specified as compatible with all resolution 633 nm MST mainframes, so that compatibility statement is your first filter. If your mainframe is not a 633 nm MST resolution system, this expander is not the right starting point regardless of the magnification you want.

The catalog description for the BEX lists an expander frame with covers, a Decollimator Mount, a Collimator Mount, a Large Fold Mirror, a Small Flip Fold Mirror, and an Accessory Receptacle. Those are the mechanical and optical pieces that make the expander work as a system. Note what is not included: the interferometer itself and other accessories such as an isolation table, 2-axis mount, or TF. Budget for those separately if you do not already own them.

Aperture and magnification: what actually changes

Aperture sets the largest beam the expander can pass without clipping. A 24-inch expander is a large-aperture system, which is why it belongs in the Large Aperture Systems conversation even though it is sold as a spare part here. If your beam is small and your mainframe is a smaller format, a 24-inch expander adds cost and alignment effort without improving the measurement.

Magnification is a ratio, not a standalone benefit. Higher magnification narrows the divergence and spreads the beam over a larger area, which can help when you need to fill a large aperture or test a large optic. The trade-off is that alignment becomes more sensitive and the assembly takes more space. The supplied catalog facts do not list a magnification value for the BEX, so treat magnification as a specification you must confirm from your mainframe documentation rather than assume. Do not guess a number from the product name.

Mounts, mirrors, and the parts people forget

The BEX includes a Decollimator Mount, a Collimator Mount, a Large Fold Mirror, a Small Flip Fold Mirror, and an Accessory Receptacle. Each of these affects how the expander integrates with your existing bench. The fold mirrors route the beam, the decollimator and collimator mounts hold the optics, and the accessory receptacle gives you a place to attach additional hardware.

Because the interferometer, isolation table, 2-axis mount, and TF are not included, plan the rest of the optical path before ordering. If you already own a Zygo mainframe and mounts, the BEX fills the expander role. If you are missing the mainframe, this is not a complete measurement system and you should not treat it as one.

Spare parts that support the same setup

Two other Zygo spare parts come up when maintaining a beam expansion setup. The High Resolution Turret Driver Board is designed for HD and DynaFiz turret systems under the Standard SKU with part code 6450-8171-01. If your turret will not index or drive correctly, this board is the targeted replacement rather than a new expander.

The Verifire MST Laser and Controller is listed under Spare Parts with standard SKU 6500-0714-01, and the description references a Toptica Laser Assembly. If your 633 nm MST source is the problem, replacing the laser and controller addresses the source, not the beam expansion optics. Separating source faults from expander faults saves you from buying the wrong assembly.

Decision rules for buying a beam expander

  • Rule 1: Confirm the mainframe compatibility line: The BEX is stated as compatible with all resolution 633 nm MST mainframes. If your mainframe is not in that family, stop and identify the correct expander for your system before ordering. Compatibility is the first gate; magnification is second.
  • Rule 2: Size aperture to the beam you actually run: A 24-inch expander suits large-aperture work. If your beam and test optic are small, a smaller expander will be easier to align and less expensive to own. Do not buy aperture you will never fill.
  • Rule 3: Separate source faults from expander faults: If the beam is weak or unstable, check the Verifire MST Laser and Controller before blaming the expander. If the turret will not drive, check the High Resolution Turret Driver Board. Diagnose the failing subsystem first, then buy the matching spare part.
  • Rule 4: Account for the parts not in the box: The BEX does not include the interferometer, isolation table, 2-axis mount, or TF. Add those to your plan if they are not already on your bench. Total cost includes the support hardware around the expander.

Product facts

  • 24 Inch High Resolution Beam Expander (BEX): 24 Inch High Resolution Beam Expander (BEX), compatible with all resolution 633 nm MST mainframes, includes expander frame with covers, Decollimator Mount, Collimator Mount, Large Fold Mirror, Small Flip Fold Mirror, and Accessory Receptacle. This is the expander to choose when your mainframe is a 633 nm MST resolution system, because the included mounts and mirrors cover the mechanical build. Interferometer, isolation table, 2-axis mount, and TF are not included, so confirm you already have them.
  • High Resolution Turret Driver Board: High Resolution Turret Driver Board is a Zygo spare part designed for HD and DynaFiz turret systems, offered under the Standard SKU with part code 6450-8171-01. If your HD or DynaFiz turret is the failing component, this board is the correct spare part. It does not expand a beam, so it is not a substitute for the BEX when aperture coverage is the goal.
  • Verifire MST Laser and Controller: Verifire MST Laser and Controller, listed under Spare Parts, standard SKU 6500-0714-01, with the description referencing a Toptica Laser Assembly. Use this when the 633 nm MST source or controller is at fault. It keeps a working expander in service instead of replacing optics that are not the problem.

Who should buy which

Best for

  • Owners of a 633 nm MST resolution mainframe who need a 24-inch high-resolution beam expander with mounts and fold mirrors included.
  • Labs already equipped with an interferometer, isolation table, and 2-axis mount who only need to add the expander assembly.
  • HD or DynaFiz turret users who need the High Resolution Turret Driver Board as a targeted spare part.

Not for

  • Mainframes outside the 633 nm MST resolution family, which need a different expander match.
  • Buyers who do not own the interferometer, isolation table, 2-axis mount, or TF and expect the BEX to be a complete system.
  • Small-beam setups where a 24-inch aperture adds alignment difficulty without measurement benefit.