These are *Kits* of parts to construct laser interferometer-based displacement measuring systems from materials about as close to stone blocks and bear skins as is reasonably possible. ;-)

However, if your goal is to end up with a system that is usable for an actual application like a CNC machine or something similar rather than simply the joy and satisfaction of being able to say you actually built the thing, consider listing 303500535042 instead.  While more expensive, it uses a commercial laser, interferometer optics, and optical receiver(s), and thus eliminates many issues of fiddly construction (fragile glass laser tube, high voltage, precision mounting and alignment, etc.).  And it in the end will almost certainly be better in terms of reliability. 

Note that displacement measuring systems are NOT rangefinders - they keep track of the CHANGE in position between the interferometer and a moving reflector and must be zeroed to a reference.  The reflector generally needs to be either a good quality cube corner or plane mirror.  A diffuse surface will NOT work.

Versions are now available for use with homodyne and heterodyne interferometers.

Note: If a kit you are interested in is out of stock, contact me for availability or alternative.

The following are the standard kits:
  • Homodyne Kit with Single frequency Laser: Includes HeNe laser tube tested for single frequency operation, heater, power supplies, optics, µSLC1, Quad Decoder, parts for thresholding to Quad A/B, and µMD2.  Native resolution with Linear Interferometer of -80 nm.  The path length difference can be up to several meters.
  • Homodyne Kit with LP Head: Similar to the one above but replaces the bare laser tube with a Linearly Polarized (NOT Low Power!) HeNe laser head (minimum power 0.7 mW) with Alden connector and matching power supply.  This eliminates virtually all wiring, is easier to mount, and no potentially shocking high voltages are involved. ;-) The resolution is similar to the one above but the path length difference must be limited to no more than +/- a few cm.  It has the same laser as in the Michelson Educational Setups I used to offer.  Parts are provided to convert from Quad-Sin-Cos to µMD2, but there is no PCB for that.  As a practical matter for a demo or proof-of-conecpt, the lower cost "Minimal Homodyne Kit with LP Head" kit, below, will be just as good.
  • Heterodyne Kit with Two frequency Laser: Includes HeNe laser tube tested for two frequency operation, Zeeman magnets, heater, power supplies, optics, µSLC1, and µMD2.  The laser tube has a minimum output power of 0.4 mW.  Native resolution with Linear Interferometer is ~158 nm.  The path length difference can be up to several meters.
  • Heterodyne Kit with High Power Two frequency Laser: Similar to above but the tube has an output power of >0.8 mW. 
  • Combined Kit for Heterodyne or Homodyne: Parts to construct both type but not at the same time.  This really doesn't make sense as the laser had to be significantly modified to switch between types and that's just asking to screw up. This option is currently disabled because it ends up being too confusing for both of us, sorry. ;( ;-)
  • Heterodyne Kit with Hewlett Packard Laser Tube Assembly: A complete assembly with glass laser tube in magnet, beam expander or collimator, waveplates, and frame replaces the individual parts of the other options. This has been deleted because the only tubes currently available are very low power - below 0.15 mW and would be challenging to stabilize and get working in an interferometer.  However, if really interested, I can provide one.
The optics included with these kits can be used to construct several types of interferometers.  With a Plane Mirror Interferometer, the resolution is improved by a factor of 2 (e.g., down to 40 nm for the homodyne interferometer or 80 nm for a heterodyne interferometer) compared to a Linear Interferometer.  For those setups that support a large path length difference, a beam expander will be required to prevent the beam divergence from being an issue.

Note that while µMD2 has no practical upper limit on counts per second, the interface electronics included in the homodyne kits are very limited, so they are recommended only for a proof of concept or student project unless you are able to construct a pair of high speed trans-impedance amplifiers whose outputs are thresholded and converted to RS422.  A schematic is in the Quad-Decoder manual or will be provided upon request.  Otherwise, the heterodyne kits are recommended.

And for this reason, the Minimal versions of the homodyne kits are probably perfectly acceptable and less expensive.

While the heterodyne native resolution is only 80 nm with a Plane Mirror Interferometer (PMI), and the homodyne native resolution is only 40 nm, for slowly changing displacement, the actual accuracy can be a few nm or even better with averaging in the GUI.

The only downside of SG-µMD2 had been that it didn't support sub-wavelength interpolation.  However,  V2.61.XX SG-µMD2 interpolation firmware now exists hot off the presses that will work for one axis, and probably for up to 3 axes. It implements phase-based interpolation with nm-scale resolution for slowly changing displacement, but now over a millisecond time scale - a thousand times faster than using GUI averaging.   For higher slew rates, the resolution should be similar to the way it was before.  So while one cannot achieve such high precision if slewing rapidly, end-point resolution and accuracy will be stellar.  Three axes are implemented but only Axis 1 has been tested so far.  Be the first on your block to try this!  But be warned, making sense out of such precision requires a special setup with immunity from vibrations and with ultra-low thermal expansion that may change the relative path lengths.  Otherwise the display will be nonsense due to the Laws of Physics. ;-) V2.61.xx is also usable without interpolation as well as for its frequency counter function.  But to be safe, stick with the default V2.20.

These are basically a combination of an unstabilized HeNe laser tube or head kit, a stabilized HeNe laser kit, or the stabilized HeNe Zeeman laser kit along with DIY interferometer optics, and the µMD0 of µMD2 Micro Measurement Display to implement a complete displacement measuring system with nanometer resolution using parts about as close to stone blocks and bear skins as is reasonably possible. :-)  The diagrams show schematic representations of typical systems as well as some of the interferometer configurations.

The following minimal systems are lower performance but still more than adequate for tracking the movement of a micrometer stage as noted.  Only a Linear Interferometer may be constructed with the parts included in the Minimal Kits.  The native resolution is the same as that of the Standard kits.  Here are the options:
  • Minimal Homodyne Kit with SF laser: Single frequency HeNe laser with µMD0.  Very limited slew rate but capable of a large path length difference.
  • Minimal Homodyne Kit with MLM laser: Unstabilized HeNe laser with µMD0.  The path length difference for this random polarized laser must be 1/2 the tube cavity length +/- up to a few cm.  This one would be great for a student project on precision measurement using the wavelength of light as a "yardstick".  One can do a lot in a few cm. ;-)
  • Minimal Homodyne Kit with LP Head: Replaces the bare laser tube with a Linearly Polarized laser head (minimum power 0.7 mW) with Alden connector and matching power supply.  This eliminates virtually all wiring, is easier to mount, and no potentially shocking high voltages are involved. ;-) .  This also includes µMD0 and the performance is similar to the one above except that the path length difference must be zero +/- up to a few cm.  It has the same laser as was in the Michelson Educational Setups I used to sell.  This is the easiest of all these kits to construct with the conversion from Quad-Sin-Cos to µMD0 done on the µMD0 PCB.
  • Laser Doppler Displacement Meter: This is very similar to the basic Heterodyne Kit with Two frequency Laser but the only optics it has are for the Linear Interferometer, which is intended to mount inside the laser enclosure along with both the REF and MEAS optical receivers.  Then the only external optic is a 1/2 inch retro-reflector for the moving target.
The accuracy with any of the kits, even the minimal ones, will be similar to that of a $20,000 interferometer-based metrology system and the entire experience could be quite rewarding.  And to put that resolution in perspective, 80 nm is approximately 1/90th the diameter of a human red blood cell, and 1/600th diameter of an average human hair.  (The commercial systems do go lower, but for many practical purposes, it is almost impossible to tell the difference.)

As general recommendations:
If this doesn't make sense, ask!

None of these undertakings are for the lazy, even the Minimal ones.  For someone who has little or no experience with lasers and electronics, it may take several months to a year or more.  For a tinkerer-scrounger type with some basic experience, it could be as little as a few hours.  Construction will require the fabrication of some mechanical parts, wiring up of electronics, and testing of the laser with the µMD0 or µMD2 Micro Measurement Display.  But any of these could make nice college-level Senior Projects especially if combined with some real application for precision measurement.

However, where enthusiasm is lacking, a halfhearted attempt will result in the parts ending up dumped in a box in your attic next to the unfinished telescope mirror. :(  Trust me, I know about unfinished telescope mirrors. :)

And these are NOT Heathkits™ - there is no complete step-by-step assembly manual for the entire system (though there are manuals with Heathkit™-style assembly instructions for the SG-µMD2, SG-OR3, and SG-AB2 PCBs.)  While there is extensive information on all the subsystems, creativity will be required to scrounge and assemble or fabricate mechanical and electrical parts not in the kit.

Having given fair warning, here is the description.  Differences between the heterodyne and homodyne kits will be noted.

HeNe laser (upper left of main photos):

For all except the kits using a linearly polarized laser head, the laser itself consists of:
  • Well behaved 4.75 or 6 inch bare HeNe laser tube.
  • DC-input HeNe laser power supply brick with ballast resistor, tube mounting brackets, and DC wall adapter.
The single and two frequency lasers also include:
  • Thin-film Kapton heater that attaches to the tube.
  • Tiny PCB to mount a PBS cube and two photodiodes for stabilization feedback.
The two frequency laser further includes:
  • Set of rare earth magnets to place surrounding the tube which should be sufficient for a 1 MHz or greater split frequency when locked.
  • Quarter Wave Plate (QWP) to convert circular to linear polarization.
  • Linear polarizer and photodiodes for detecting REF and MEAS during testing.
Assembly of the lasers differ slightly:
  • The basic laser is similar for all consisting of the laser tube, HeNe laser power supply, and DC power pack.
  • For a stabilized single frequency laser, the thin-film heater is attached to the HeNe laser tube and the polarizing beam-splitter and photodiodes are used to provide optical feedback to control the power to the heater so the amplitude of the X and Y components are equal.
  • For a stabilized two-frequency HeNe Zeeman laser, in addition to the heater, a series of magnets are configured to surround the tube and provide an axial magnetic field.  Some experimentation will be required to optimize the configuration of the small rare-earth magnets.  7 strips of 7 magnets all pointing the same way should be sufficient to provide a locked split frequency of at least around 1 MHz but your mileage by vary.  Additional magnets can be added to boost it somewhat (but there is a limit).  The QWP then converts the circular polarization from the tube inside the magnet to linear polarization in X and Y.
  • A beam sampler (included) can be used to divert a portion of the beam for use for normal 2 mode stabilization.  When the amplitude of the X and Y components are equal, the laser will be locked correctly.  For the Zeeman laser, the two frequency components will be present in the output.  A pair of beam samplers will generally be used to provide the feedback and REF signal.  For some lasers, the waste beam out the back can be used for feedback and/REF but it may be very weak.
µSLC1 using Arduino (stabilized single and two frequency lasers ONLY, upper right of main photos):
  • Atmega 328 Nano 3.0 Arduino compatible microprocessor PCB with µSLC1 firmware preloaded.
  • A BLANK PCB Rev 1.1 or higher.  The completed controller using the PCB is shown in the sixth photo.
  • Most other parts to construct a digital controller - socket, LEDs, resistors, connectors, etc.
  • 12 VDC wall adapter for heater and optical receivers - styles may vary (not shown).  OR3 will run on 12-15 V.
  • Links to µSLC1 GUI, firmware, and assembly and operation manual.
    µSLC1 is also available by itself.

Interferometer (all except Minimal Kits, lower right of main photos):
  • 1/2 inch Polarizing Beam-Splitter (PBS) cube.
  • 2 each 1/2 inch retro-reflector (cube-corner) prism.
  • 1 small planar (dielectric or aluminum coated) mirror, generally intended to divert the beam from the interferometer to the detector.
  • 1 "large" (1/2") planar aluminum coated mirror on cheesy but usable kinematic mount, may be removed.  This would be the remote reflector for the Plane Mirror Interferometer or High Stability Plane Mirror Interferometer, not for the Linear Interferometer.  Not in minimal kits.
  • 2 each Quarter Wave Plates (QWPs).  Not in minimal kits.
These parts can be used to construct a Linear Interferometer, Plane Mirror Interferometer, Single Beam Interferometer, Angular Interferometer, Straightness interferometer, and more.  (But not at the same time!)  If you would prefer to skip building the interferometers and use HP / Agilent / Keysight optics cheating just a bit :), that can be arranged with an adjustment in cost using parts from me or elsewhere.  Inquire if interested.  The interferometer is probably the most dicey assembly in terms of construction and alignment.  But then you won't be able to claim you built this thing from scratch if that is just bought!

Only a Linear Interferometer may be constructed using the Minimal kits.

Detectors:
  • Heterodyne: 2 each of the OR3 optical receiver kit.  OR3 provides capabilities similar to that of the HP 10780 or Excel 1031 optical receiver at up to more than 3 MHz.  This will definitely be more work than making a cable but will add to the DIY experience and relegate cheating guilt only to the laser itself. ;-)  A photo of the assembled SG-OR3 PCB is shown along with the "Heterodyne Kit" and "Combined Kit for Het or Hom" selections.  OR3 consists of a 1.0 x 2.75 inch PCB and runs on 12 to 15 VDC.  It's cute. ;-)  Like the commercial optical receivers, the input is a photodiode and the output is RS422 compatible with µMD2.  Heathkit™-style assembly instructions are provided. However, since this includes a large number of discrete components whose placement and values matter, some electronics debugging skills will be highly desirable.  There is a link to OR3 on "Sam's Electronics and Laser Kit Information and Manuals" page.  Google will find it.

    SG-OR3 kits are NOT available by themselves but blank PCBs are, and along with common parts from an electronics distributor can be used.  A link to a Digikey "CART" including most of the parts is in the SG-OR3 assembly manual.
If you are the lazy type and don't want to construct OR3, I may have a limited number of HP or Excel optical receivers available at extra cost.  You can also hunt for them elsewhere on eBay.  But if you are the lazy type, the entire DIY Interferometer Displacement Measurement System Kit is definitely NOT for you! :( :)
  • Homodyne: Parts for quadrature sin-cos decoder includes variable attenuator plate to be used as a Non-Polarizing Beam-Splitter (NPBS), a piece of circular polarizer sheet (LP+QWP), a piece of LP sheet, two photodiodes, two 1M trim-pots as a adjustable loads, and two 100K ohm resistors as fixed loads.  Its output will be Quad Sin/Cos with a p-p voltage of up to a few V for a typical 0.5-1 mW laser.  for conversion to Quad A/B (TTL) order the version with µMD0 since it has the thresholding or use your own parts for that.  Note that additional electronic components will be required for a high speed interface including a dual trans-impedance op-amp circuit with gain and offset adjustments.  Parts for this are NOT included but a schematic to get you started is available in the manual.
  • (A high quality 10 mm Non-Polarizing Beam-Splitter Cube (NPBSC) is available in place of the variable attenuator plate for an additional $25.  This mounts on the same PCB and is slightly easier to align and virtually guarantees nearly equal amplitude Sin/Cos signals.  Inquire if interested and I will create a Special Option in the listing which includes it.  Less expensive NPBSs tend to not be very "Non-Polarizing". ;-)  But as a practical matter, this luxury really isn't needed.)
  • The QAB2 design is available including a blank PCB, but it is NOT included in the standard Hom and Het+Hom kits.  (A populated QAB PCB is shown in the photo.) QAB2 has a bandwidth exceeding 3 MHz so it should suffice for any DIY application.  QAB2 consists of a 1.6 x 2.25 inch PCB  and runs on 12 to 15 VDC.  It has the photodiodes for input and RS422 outputs compatible with µMD2.   Heathkit™-style assembly instructions will be provided.  However, it may not be that stable thermally so some fiddling may be required.  That is why the complete kit is not included as an option.  There is a link to QAB2 on "Sam's Electronics and Laser Kit Information and Manuals" page.  Google will find it.  The kits in this listing ONLY include the basic parts to convert to TTL.
Measurement Displays (lower left of main photo):

The µMD2 display portion for the Standard kits contains:
  • SG-µMD2 PCB and all electronic components.
  • USB A male to USB B Micro male cable.
  • Headers or screw terminal blocks for 1 axis.
  • OLED display.  This may be useful for testing but does NOT provide anything like the µMD GUI.
  • Links to µMD2 and µMD0 Installation and operation manuals. These include full specifications, assembly and wiring instructions, Windows GUI operation, and links to the latest firmware and GUI software.
The "Minimal Homodyne" systems include parts for µMD0 including the SG-µMD0 PCB.

Documentation including construction guidelines, and friendly lifetime tech support will be provided.  "Lifetime" is defined as either yours or however long you remain interested in this stuff, but is assumed to terminate sometime shortly after the Universe ends.

One of the short Scanning Fabry-Perot Interferometer (SFPI) kits (#s 1-8 in listing 303543775362) would permit the longitudinal modes of the laser to be displayed in real-time.  While the resolution using one of these short SFPIs will NOT be sufficient to see the individual frequencies of the two-frequency laser, it can be used to confirm that there are no rogue modes present, and with other lasers as a general purpose laser spectrum analyzer for wavelengths in the yellow-red range.  Some of the long SFPIs can resolve the two frequencies if that's what you'd really like to see but they can really only be justified for true SFPI junkies. ;-)

General info on home-built stabilized HeNe lasers including complete schematics for analog controllers may be found in the Sam's Laser FAQ chapter: Home-Built HeNe laser.  (Google will find it - eBay is anal about including off-site links.)  Only basic mechanical and electronic skills are required to complete the laser.  As noted, construction guidelines and email tech support will be provided.  However, this is NOT a turnkey system.  Some assembly is definitely required.  How many times have I said that? ;-)

The HeNe laser tube and its power suppply are used but tested and guaranteed to be healthy be and  suitable for the type(s) of interferometer(s) in the kit.  All other parts are new.

The diagrams above show the hookup for powering the tube itself and the general scheme used for stabilization .  Detailed instructions may be found by going to repairfaq.org/sam/manuals.  Of critical importance is that the tube be installed as shown in the diagram.  However, the beam may exit from either end depending on the particular tube that in the kit.  The tube may light and appear to work even if installed backwards, but it is likely to fail quickly.  Failure of the tube due to incorrect wiring is easily detected via forensic analysis and not covered by the 30 day warranty.

For international buyers, the wall adapters will run on 100-240 VAC but will either have US plugs or a socket for a detachable cord.

Specific models of parts may vary depending on availability and may not match the photos precisely.  They are fully tested prior to shipping.

The Micro Measurement Displays (µMD0 or µMD2) provide most of the capabilities of an HP-5508A and more.  The firmware requires a PC with USB port running Windows XP or later and .NET 4.0 or later for the custom µMD application (which is the same for all).  The PC is NOT included but most systems (desktops, laptops, or netbooks) more recent than the Jurassic period should be satisfactory. :)  So dust off that old computer and put it to good use!  Sorry, µMD does not run on a phone - yet!  The Graphical User Interface (GUI) provides real-time displacement and velocity measurements using common interferometer optics on up to three independent axes, as well as optional frequency analysis of the displacement data.  µMD also supports straightness and angle measurements with appropriate optics and allows for their parameters to be entered if non-standard.  Environmental compensation parameters (temperature, pressure, humidity) may be entered manually.  See the photos for examples of the typical display.  Other features include logging so that data can be exported to a data analysis application like Matlab or Excel; and Test Mode which has it's own function generator for simulated data which can be displayed and processed just like real data for verifying behavior or just checking out operation.  And for custom applications, the GUI can be bypassed entirely with data input directly to your custom software.  The µMD0 and µMD2 PCBs run from USB 5 VDC.

If you are interested in actually using these parts in a metrology application (as opposed to simply for the pleasure of perpetual construction, testing, and adjusting), I recommend one of the Heterodyne Kits as they are more capable, easier to align, and generally more useful.  For just dipping your feet into interferometery, one of the Minimum Homodyne Kits would probably suffice.

Much more information on homodyne and heterodyne interferometry, stabilized HeNe lasers, and other related topics may be found in "Sam's Laser FAQ".

Details on the kits may be found at "Sam's Electronics and Laser Kit Information and Manuals", which also have links to the above.

Google will find these.

And there is a lot to digest here, so please feel free to contact me directly via eBay or the Manuals page with questions.

If you have no idea what this stuff is, you probably don't need any! :)

Returns will be accepted only if everything is in identical condition to how it was received, or if incorrect parts were sent by mistake. Where parts are damaged (like the PCB due to using a butane torch instead of a proper soldering iron), a partial refund may be considered.  But please understand that the PCB in that case would be scrapped and significant time and effort may be required to retest other parts like the laser.

eBay International Shipping is likely to be the least expensive reliable shipping method for overseas buyers.  However, it may not support your country and/or lists "lasers" as prohibited items.  But since this is a kit, there have so far been no problems shipping similar sets of parts.  I can also use the shipper of your choice if you do all the "paperwork" and send me the shipping documents.  Or the kit can be sent to a USA address and accepted there.  Then you do the overseas shipping. ;-)

Thanks for looking!

--- sam