Scanning Fabry-Perot Interferometer KITs for Violet-Red Wavelengths ~400-700nm

Slide Slide Slide Slide Slide Slide Slide Slide Slide Slide Slide Slide
$215.0
Type
Basic SFPI YOR 590-650 nm
Dual Polarization
Yes
Mini Laser Mode Analyzer Parts
Yes
Brand
Unbranded
condition
New – Open box
These are kits of parts to construct several different types of Scanning Fabry-Perot Interferometers (also may be used as laser spectrum analyzers, tunable etalons, or tunable optical frequency filters). The usable wavelengths extend somewhat beyond the limits listed but how far cannot be guaranteed.

(The Michelson interferometer kits have moved to their own listing: 303925810399.)
THIS LISTING has replaced my other listings: "One Stop Shopping" for DIY SFPI kits now including versions for Red, Orange, Yellow, Green, Blue, and Violet wavelengths. ;-)  Shipping is usually same day for non-Deluxe kits but may be up to 5 days if parts need to be ordered.

Sorry, nothing much beyond 700 nm.  I thought I had a supplier but the mirrors turned out to not be usable for an SFPI.

Not all the options in this listing are shown in the main photo. Versions of these SFPI kits are also available using any of the broadband or other mirrors in listing #303503394501.   Inquire if interested.

Sorry, no short cavity spherical mirror SFPI kits for wavelengths below 590 nm are currently available.  And, there are only planar mirror SFPI kits for wavelengths above 650 nm, and none beyond 1,100 nm.

And mirrors for the GY 525-600 nm are out of stock.  However, substitutes with a 1 m RoC and acceptable reflectance may be available, but the usable area is only 3 or 4 mm in diameter.  Inquire if interested.
Types 1-8 SFPI YOR (Yellow-Orange-Red) can be used to construct general purpose Laser Spectrum Analyzers (LSAs) for displaying the complete set of longitudinal modes of YOR 590-650 nm HeNe lasers. Types 1 or 2 are probably what you really want since these are most useful for general purpose use and have capabilities similar to those of common commercial SFPIs covering the same wavelengths. They are also the same kits as offered in the separate SFPI listings I used to have. The others are for specialized SFPI nerd applications and may be far more challenging to construct and get working as well. :-)
There are now a few complete Mini Laser Mode Analyzer (mLMA1) kits available.

However, mLMA1 is really intended for short SFPIs like Types 1-8 SFPI YOR - performance with the other SFPIs may be unsatisfactory.  Regardless of SFPI type, a real function (ramp) generator and oscilloscope are highly recommended for initial setup at least.  Inquire for more details or go to the mLMA1 Web page.

All mirrors are new/NOS.  They are 7.75 mm diameter except as noted.

Note: All selections must have valid entries for the correct price to appear. If the behavior is not as expected, please contact me. Creating these multi-option listings is a bit dicey and even after many years, eBay has not fixed some significant bugs. And sorry, I have no control over what default price appears in the listing. :-) Note that if an entry is grayed out for a particular selection, it usually means the option doesn't apply as it would not work well or at all with the selected mirror set and/or resonator length, is NOT available, or I forgot to update the available quantity.  Inquire if interested.

Spherical Mirror SFPI Kits:

Spherical mirror SFPIs are the most common type for general purpose use as they are easy to align and it's usually possible to avoid back-reflection into the laser by careful alignment with the beam slightly off-axis.  However, for any given set of mirrors, they have a limited set of mirror spacings which may be used and thus only a few options for FSRs.  The most common is called "confocal" with a cavity spacing equal to the RoCs of the mirrors, but others may have benefits either in terms of space or FSR.
  • The non-Deluxe kits include a pair of mirrors, PZT with center hole, and photodiode only.  Mounting is left to your imagination, creativity, and budget.
  • The Deluxe and Deluxe+ kits add combinations of Thorlabs cage parts to construct an SFPI frame.  There may be other parts included in specific cases - check the detailed descriptions below.
  • Long radius mirrors may also be used with shorter frames using higher orders of N.  See #23 below and the description of mode degenerate SFPIs.  Inquire for more information.
  • Note that the "+" option which substitutes an adjustable mount for one of the cage plates in some of the Deluxe spherical SFPIs is not really required for those using the 42 mm RoC mirrors.  With care in centering of the mirrors during assembly, they will work just fine using only the entire frame for alignment.  Thus this option may be grayed out - if you really want the adjustable mount, ask me to enable it. ;-)
  • And you'll still get friendly tech support even if you buy parts directly from Thorlabs or elsewhere. ;-)
Available Spherical Mirror SFPI Kits using 42 mm RoC Mirrors:
  1. Basic SFPI YOR 590-650 nm: ~4.2 cm RoC mirrors with PZT and photodiode ONLY. Covers popular Yellow through Red wavelengths. Confocal FSR of ~1.79 GHz. Finesse at 633 nm: > 200, at 594 nm: typically > 100. Measured reflectance of a sample of the mirrors: 99.6%@594 nm, 99.7%@605 nm, 99.8%@612 nm, 99.8%@633 nm. More below. The diagram of the SFPI assembly is a serving suggestion built using scrap metal and common hardware (additional parts not included). The scope display shows the modes of a 5 mW 633 nm HeNe laser using the mirrors in this kit and either an SFPI assembly similar to the one in the diagram, or the deluxe verson below. (For anyone who has been paying attention, the RoC used to be 4.3 cm, but it has been measured for one pair of mirrors more accurately using a selectable FSR SFPI by recording the exact locations of the first few mode-degenerate spacings.)



  2. Deluxe SFPI YOR 590-650 nm: Basic SFPI parts PLUS a 4 inch long frame using Thorlabs 30 mm cage components and focusing lens. The photo on the right shows a complete SFPI head mounted on an adjustable metal base (not included).

     

  3. Deluxe+ SFPI YOR 590-650 nm: Replaces one of the cage plates in the Deluxe kit with an adjustable mount. This may make your life easier though it is not really needed as noted above.
  4. Deluxe Short SFPI YOR 590-650 nm: Similar to Deluxe SFPI parts but with a 3 inch long frame using Thorlabs 30 mm cage components and focusing lens. 1/2 Confocal spacing recommended, FSR of 2.38 GHz. Finesse at 633 nm: > 133; finesse at 594 nm > 65.
  5. Deluxe Mini-SFPI YOR 590-650 nm: Basic SFPI parts except for ~20 mm instead of 27 mm PZT, PLUS a 2 inch long frame using Thorlabs 16 mm cage components and focusing lens. 1/2 Confocal spacing recommended, FSR of 2.38 GHz. Finesse at 633 nm: > 133; finesse at 594 nm > 65. This head is really compact and cute. ;-) The second photo shows a completed head also including a dual polarization beam sampler in front for the mode display of mLMA1 (not included).

     

  6. Deluxe+ Mini-SFPI YOR 590-650 nm: Replaces one of the cage plates in the Deluxe kit with an adjustable mount. Even less important. :)
  7. Deluxe Micro-SFPI YOR 590-650 nm: Similar to Deluxe Mini-SFPI YOR 590-650 nm but with 1.5 inch long frame and ~20 mm diameter PZT. Must use cavity parameter N of 3 or greater. Finesse should still be way more than high enough for use with mLMA1. For N=3 (no space for lens mount), cavity length = ~2.1 cm, FSR of ~2.4 GHz, finesse >100. For N=4, cavity length = ~1.23 cm, FSR of ~3.05 GHz, finesse >65.
  8. Deluxe Nano-SFPI YOR 590-650 nm: Similar to Deluxe Micro-SFPI YOR 590-650 nm but with ~1x1x1 inch frame and no lens or mount. Must use cavity parameter N of 4 or greater. The display is of the same Melles Griot 05-LHR-151 ~5 mW HeNe. For N=4, cavity length = ~1.23 cm, FSR of ~3.05 GHz, finesse >65. The Finesse is still high enough for use with mLMA1. Super compact and cute. ;-)

  9. Selectable FSR SFPI YOR 590-650 nm: This setup permits the cavity spacing to be easily changed and then fine tuned to experiment with almost any usable mode degenerate spacing shown in the table below, and more.  It consists of a Thorlabs 6 inch rail with two platforms on a baseplate for coarse positioning, small linear stage for fine positioning, mirror mounts, the same mirrors as in the Basic SFPI YOR 590-650 nm, PZT and photodiodes with custom PCB for mounting. There is also a version with a ball bearing rail instead.  See "Construction Guidelines for the Selectable FSR Scanning Fabry-Perot Interferometer Kit 1".  Google will find it.  Longer versions may be available eventually.  Note: If you will only be using the SFPI at a fixed spacing, the setups using Thorlabs cage parts are probably more stable.  The benefit with this one is ease of cavity length adjustment.  Diagram on left, photos of prototype before adding mirrors, PZT, and detectors on right.  Note: I am no longer offering complete kits for this, but may have sets of parts where some like the baseplate may not be finished.  These would be at a somewhat lower cost.  Ask.
   
Available Spherical Mirror SFPI Kits using Longer Radius Mirrors:
  1. Mid SFPI parts for YOR 590-650 nm: 13.6 cm RoC mirrors with PZT and photodiode ONLY. Confocal FSR of ~551 MHz, R 98-99% at 633 nm, finesse from 75 to 150. R > 97% 594-650 nm. The diameter of the mirrors is approximately 10 mm but only the central 4 mm or so is coated.
  2. Deluxe Mid SFPI parts for YOR 590-650 nm: This adds an 8 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end.
     

  3. Long SFPI parts for YOR 590-650 nm: 30 cm RoC mirrors with PZT and photodiode ONLY. Confocal FSR of 250 MHz. Finesse at 633 nm > 100. Measured reflectance of a sample of the mirrors: 95.7%@594 nm, 97.6%@605 nm, 98.2%@612 nm, 98.8%@633 nm. So this would still be useful for determining SLM behavior over the YOR wavelength range and the generally lower reflectance makes setting up aligning simpler. At 544 nm, R is around 40%; above 633 nm, R has not been measured but it may be higher over some range.
  4. Deluxe Long SFPI parts for YOR 590-650 nm: This adds a 14 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end.

     

  5. High Resolution SFPI YOR 590-650 nm: 100 cm RoC mirrors with PZT and photodiode ONLY. Confocal FSR of 75 MHz. Finesse at 633-594 nm: > 200. Measured reflectance of a sample of the mirrors: >99.8%@594 nm, 99.8%@605 nm, 99.8%@612 nm, 99.4@%633 nm. Should be acceptable for some range beyond 650 nm but how far has not been tested.
  6. Deluxe High Resolution SFPI YOR 590-650 nm: This adds a 14 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end similar to those for the Long SFPI, above, and below. (The adjustable baseplates, and iris diaphragm at the front are NOT included but are available, see the options below.) When set to a mirror spacing of around 29 cm (N/k=4/1 in the chart below), the result should be an effective FSR of around 129 MHz with a finesse of more than 200 for 633 nm and probably somewhat higher for 594 nm. This will easily resolve the split modes of most high-field regime axial Zeeman lasers like those from HP/Agilent including all 5517s, 5518A, 5519A/B, 5501B, and N1211A as shown in the last photo and below. The split frequency is around 1.5 MHz. There is no affordable commercial instrument with this high performance.

     

  7. Deluxe+ High Resolution SFPI YOR 590-650 nm: This adds a set of 8 inch cage rods to extend the frame to 22 inches so the cavity length may include the half-confocal spacing (your choice but you must specify in a message, or else it will be my choice).  (The iris diaphragm and bars with adjustment screws are NOT included.)  With a mirror spacing of around 50 cm, the resolution should be better than 500 kHz.

     

  8. Ultra-High Resolution SFPI YOR 590-650 nm: Hi-Q 99.99+% HR 60 cm RoC mirrors with PZT and photodiode ONLY. Half-Confocal FSR of ~167 MHz. Finesse at 633 nm: is at least 1,500 and may be much more with a mode-matched input. Measured reflectance of a sample of the mirrors: >99.993%@633 nm and appears to be similar at 594 and 612 nm but not precisely measured. The only reason to want to build one of these is to have bragging rights to the highest finesse SFPI on your block. ;-)
  9. Deluxe Ultra-High Resolution SFPI YOR 590-650 nm: This adds a 14 inch long frame using Thorlabs 30 mm cage components, adjustable mounts at both ends with the front one on a translation stage (styles may vary). (The iris diaphragm at the front is not included but the front and back height adjustment plates and some other odds-and-ends will be included.  An iris is available, see the options below.) The resolution using the exact rig below is better than 50 kHz. The screen shots show the display of a single frequency Spectra-Physics 117A laser and the split modes of an Agilent N1211A two frequency laser separated by 520 kHz. And it only requires around 37 hours of fiddly alignment in a pitch black room. :) And if you're a real masochist, extend the frame to 26 inches for the full confocal spacing and nearly double the resolution. Better have a sleeping bag and snacks handy. ;-)

     

  10. Universal SFPI YOR 590-650 nm: This consists of pairs of 7.75 mm diameter 4.2 cm RoC and 100 cm RoC 99.5% mirrors and a pair of 60 cm RoC 99.99+% mirrors, 3 holey PZTs, and associated photodiodes, along with cage rods to construct a frame from 2 to 24 inches in length, adjustable mounts, translation stage, iris, cage plates, adapters, and most other hardware to construct nearly all of the SFPIs above and more. This is the ultimate kit for the SFPI junkie in your life who would love to spend several months or more playing with mirrors. "It's all done with mirrors." ;-)
  11. High Resolution SFPI GY 525-600 nm: 100 cm RoC mirrors with PZT and photodiode ONLY. Covers popular Green through Yellow wavelengths. Confocal FSR of 75 MHz. Finesse at 532 and 544 nm: >200. Measured reflectance of a sample of the mirrors: 95%@488nm, 99.7%@514 nm, 99.8%@544 nm, 99.5%@594 nm. So good down to 514 nm at least.
  12. Deluxe High Resolution SFPI GY 525-600 nm: This adds a 14 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end like the Deluxe High Resolution SFPI YOR 590-650 nm, above. When set to a mirror spacing of around 29 cm (N/k=4/1 in the chart below), the result should be an effective FSR of around 128 MHz with a finesse of 150 or more from 530-610 nm.
  13. Deluxe+ High Resolution SFPI GY 525-600 nm: This adds a set of 8 inch cage rods to extend the frame to 22 inches so the cavity length may include the half-confocal spacing (your choice but you must specify in a message, or else it will be my choice).
  14. Deluxe+ High-N SFPI GY 525-600 nm: This has the same frame as the Deluxe+ SFPI YOR 590-650 nm (including an adjustable mount at one end) but with the GY 525-600 nm mirrors, so it must be used with an "N" value of 9, 10, or above.  (See below for an explanation.) At a spacing of 4.9 cm (N=10), the FSR will be 306.3 MHz and the finesse should be at least 50, possibly over 100 with careful alignment and very clean mirrors.  This doesn't compare to a high resolution SFPI but would be more than sufficient to monitor a green or yellow laser for single frequency/single longitudinal mode (SF/SLM) operation.  However alignment is definitely more critical than for the short confocal SFPI and back-reflections into the laser aperture may be unavoidable.  Other frame lengths may be available.  The screen shot below shows a test with a Coherent 215M 532 nm SLM laser.


  15. High Resolution SFPI BG 488-550 nm: 140 cm RoC mirrors with PZT and photodiode ONLY. Covers popular Blue through Green  wavelengths. Confocal FSR of 54 MHz. Finesse at 532 and 544 nm: >200. Measured reflectance of a sample of the mirrors: 99.5%@544 nm. Spec'd reflectance at 488 nm: 96.5%.  Probably good for somewhat beyond 544 nm but NOT much below 488 nm or to 594 nm. There is at least one set with much higher R at 488 nm: 99-99.7%.  Inquire if interested.  LO1207.
  16. Deluxe High Resolution SFPI BG 488-550 nm: This adds a 22 inch to 24 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end like the Deluxe+ High Resolution SFPI YOR 590-650 nm, above. When set to a mirror spacing of around 41 cm (N/k=4/1 in the chart below), the result should be an effective FSR of around 92 MHz. LO1207.

  17. Long SFPI B1 450-520 nm: 60 cm RoC mirrors with PZT and photodiode ONLY. Covers popular Blue argon ion and DPSS wavelengths. Confocal FSR of 125 MHz. Measured reflectance of a sample of these mirrors: ~98.5%@458 nm, 97%@488 nm, ~98%@514 nm. Finesse at 458 nm: > 60. With a spacing of 30 cm, finesse at 458 nm (N/k=3/1 in the chart below): >30. FSR ~170 MHz.
  18. Deluxe Long SFPI B1 450-520 nm: This adds an 14 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. (Same frame as the Deluxe Long SFPI, above.)
  19. Long SFPI B2 458+514 nm: 30 cm RoC mirrors with PZT and photodiode ONLY. Dual Blue 458 and 514 nm argon wavelengths, good at Blue 457 nm DPSS. Confocal FSR of 250 MHz. Measured reflectance of a sample of these mirrors: >99%@458, >97%@514 nm, but much lower in between. Finesse at 458 nm > 200, at 514 nm > 30. With a spacing of 15 cm, finesse at 458 nm: > 100, at 514 nm >15. Confocal FSR of ~340 MHz.
  20. Deluxe Long SFPI B2 458+514 nm: This adds a 14 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. (Same frame as the Deluxe Long SFPI, above.)

  21. Basic VIS SFPI RGB 400-750 nm: 12.7 mm diameter mirrors coated for 400-750 nm with an RoC of 50 mm resulting in an FSR of around 1.5 GHz.  The finesse should be greater than 150 for a confocal SFPI.  These mirrors are back-side polished but NOT AR-coated.  Includes PZT and photodiode.  Under consideration but ETA unknown.
  22. Deluxe VIS SFPI RGB 400-750 nm: Adds 4 inch long frame using Thorlabs 30 mm cage components and focusing lens.
  23. Deluxe+ VIS SFPI RGB 400-750 nm: Replaces one of the cage plates in the Deluxe kit with an adjustable mount. This may make your life easier though it is not really needed as noted above.
Planar Mirror SFPI Kits:

Planar SFPIs have the advantage that the mirror spacing is not critical and only determines the FSR so it can be set over a wide range.  And for very large FSRs (many GHz), there is no choice as spherical mirror SFPIs cannot be built with an FSR much over 30 GHz (and none of the spherical SFPI kits comes even close to this).  However, alignment is much more critical and optimal alignment results in a strong reflection directly back into the laser, which may destabilize or in extreme cases, even damage it.  Therefore, it may be necessary to add some type of optical isolator and/or sampler to minimize the back-reflections reaching the laser.
  • The non-Deluxe kits include a pair of mirrors, PZT with center hole, 2 additional PZTs for optional fine alignment, and photodiode only.
  • The Deluxe and Deluxe+ kits add combinations of Thorlabs cage parts to construct an SFPI frame.  There may be other parts included in specific cases - check the detailed descriptions below.
Alignment precision beyond what a typical adjustable mirror mount can provide may be required, so all the Planar kits include additional PZTs to construct a simple kinematic micro-aligner.  This are optional as an adjustable mount may be sufficient, but will be a possibility if needed.
Available Planar Mirror SFPI Kits:
  1. Planar SFPI parts for YOR 594-700 nm: This consists of a pair of planar 7.75 mm diameter mirrors, PZT with center hole and two additional PZTs without a hole for fine angle micro alignment, and a photodiode. The measured reflectance of a sample of these mirrors: 95%@594 nm, 99.3%@605 nm, 99.7%@612 nm, 99.93%@633 nm. At 544 nm, R very low and would not be useful; above 633 nm, R is still very high at 700 nm but has not been measured.  If the wavelength of interest is between 650 and 700 nm, I will attempt to test.  Note that this is HR for 633 nm so not many photons will get through.  These mirrors are NOT AR-coated.
  2. Deluxe Planar SFPI parts for YOR 594-700 nm: This adds an 8 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. Other frame lengths are available.
  3. Planar SFPI parts for YOR 590-650 nm: This consists of a pair of planar 19 mm diameter mirrors, 35 mm PZT with center hole and three similar PZTs without a hole for fine angle micro alignment, and a photodiode. The measured reflectance of a sample of these mirrors: 99.8%@594 nm, 99.8%@605 nm, 99.82%@612 nm, 99.75%@633 nm .  At 544 nm, R is around 93%; R is still very high at 700 nm but has not been measured.  If the wavelength of interest is between 650 and 700 nm, I will attempt to test.  These mirrors have planar windows bonded to their fine-ground rear surfaces (which is acceptable for the SFPI) and are NOT AR-coated.
  4. Deluxe Planar SFPI parts for YOR 590-650 nm: This adds an 8 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. Other frame lengths are available.
  5. Planar SFPI parts for BG 500-550 nm: This consists of a pair of planar 7.75 mm diameter mirrors, PZT with center hole and two additional PZTs without a hole for fine angle micro alignment, and a photodiode. The measured reflectance of a sample of these mirrors: 99.9+%@532 nm and 544 nm. I am listing this for green-blue wavelengths but will need to confirm if there is interest as it has not been measured below 532 nm. Note that this is HR for 544 nm so not many photons will get through. These mirrors are NOT AR-coated.
  6. Deluxe Planar SFPI parts for BG 500-550 nm: This adds an 8 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. Other frame lengths are available.
  7. Planar SFPI VB 400-520 nm: PLANAR mirrors with one PZT with center hole and 2 additional PZTs without for fine angle micro alignment, and a photodiode. Violet-blue wavelengths for diode, HeCd and argon lasers. Labeled reflectance: ~99.5%@442 nm, measured reflectance of a sample of these mirrors: >98.8%@410 nm, >99.3%@458 nm, >99.6%@488 nm, 98.7%@514 nm.  The distance between the mirrors isn't critical and only determines the FSR. Finesse should be greater than 250 over the wavelength range 410-490 nm or more and still greater than 100 at 410 and 514 nm. One photo shows the parts included in the Planar SFPI VB 400-520 nm. The diameter of these mirrors is 15 mm.
  8. Deluxe Planar SFPI VB 400-520 nm: This adds an 8 inch long frame using Thorlabs 30 mm cage components, adjustable mount at one end. Other frame lengths are available.
Electronics and Miscellaneous Parts:
  1. mLMA1 Electronic Parts ONLY: Components needed to construct Mini Laser Mode Analyzer but NO OPTICS.

     

  2. mLMA1+Dual Pol MS Parts ONLY: mLMA1 electronics parts as above (with or without YOR 590-650 dual polarization for the SFPI) and also dual polarization mode sampler parts adding a 45 degree sampler plate, 4x4x4 mm YOR 590-650 nm PBS cube, and 2 photodiodes. ONLY AVAILABLE FOR YOR 590-650 nm.
  3. Dual Pol Parts YOR 590-650 nm: 4x4x4 mm PBS cube for 590-650 nm and silicon photodiodes. These may be used for the SFPI and mode display of the mLMA1. A closeup of a completed dual polarization detector assembly on a Perf board is shown.  But an SG-DET2 PCB with sockets for the PDs, protection resistor, bypass cap, and 4 pin screw terminal block is shown on the right constructed for side entry (top) or back entry (bottom) and the SG-DET2 or similar blank PCB is included.

       

  4. Dual Pol Parts V 400-420 nm: 3x3x3 mm PBS cube for 400-420 nm, other parts similar to above.


  5. PZT with Center Hole ONLY: The same type of holey beeper "drum head" PZT used in all these SFPI kits. The standard version is 27 mm in diameter with a 4-6 mm diameter hole. Other diameters and hole sizes may be available. Those with a larger diameter and/or smaller holes are more sensitive in terms of V/FSR. Additional standard PZTs WITHOUT holes are also available at $2.50 each.


  6. mLMA1 BLANK PCB ONLY: All the parts are readily available and the firmware link is in the mLMA1 manual.
Additional information and options:

The values for finesse are estimates except as noted but should be very conservative. I've seen samples of the mirrors in SFPI Basic, Deluxe, and Mini Deluxe kits YOR 590-650 nm providing a confocal finesse of over 500 at 633 nm with careful mode matching and alignment. But your mileage may vary.

Confocal FSR is c/4L (c = speed of light, L= RoC) and confocal finesse is approximately 3/[2(1-R)] for R close to 1 (100% reflectance). Planar FSR is c/2L and planar finesse is approximately 3/(1-R). But for the planar SFPI, alignment is super critical and when perfectly aligned, there will be back-reflections directly into the laser, which may destabilize it.

The dual polarization option adds:
  • A small polarizing beam-splitter cube.
  • A second photodiode.
This capability is useful primarily for 633 nm random polarized HeNes where adjacent longitudinal modes are (usually) orthogonally polarized, and being able to view them separately is desirable. This is a capability that no commercial SFPI provides. ;-) The last photo shows a dual SPFI display of a 5 mW random polarized HeNe laser that has problems. If interested in this option for other kits where it's not an option, ask. It will be the same cost but the only PBSs available cover YOR 590-650 nm and V 400-420 nm.

The first (after the main photo) shows the typical 7.75 mm diameter mirrors, PZT, and PD provided in all SPFI kits EXCEPT the Planar. The mirrors are AR-coated on the other surface. The AR coating is optimum at the specified wavelength(s) but should be satisfactory over a range of values on either side. The mirrors shown are for the Basic, Deluxe, and Deluxe-Mini SFPI YOR 590-650 nm kits. The mirrors for most of the others are of similar size, though the curvature is not as pronounced and the color may differ. Exceptions are mirrors for the Mid SFPIs (~10 mm diameter) and Planar SFPIs (~7, ~12.7, or ~15 mm diameter depending on type).

The diagram shows the optical paths of a confocal SFPI. A typical SFPI display of the longitudinal modes of a 5 mW red HeNe laser built using the parts in the Basic, Deluxe, or Mini Deluxe kits is shown in the forth graphic. Other graphics show the completed Deluxe-Mini SFPI YOR 590-650 nm assembly. The focusing lens is on the left, the input mirror is in the center, and the output mirror on PZT is on the right. The photodiode is hidden behind that mirror. Some mechanical skills and assorted readily available materials will be required to construct the SFPI, which will enable the longitudinal modes of most TEM00 red HeNe lasers to be displayed in real time. These can also be configured with a smaller mirror spacing which may have some benefits. For example, with a mirrors at 1/2 the confocal spacing, while the finesse is slightly lower, the FSR increases to 2.33 GHz.

Shorter implementations of the spherical mirror SFPIs like the "Hi-RES" and "Long" SFPIs may be constructed that are more manageable in terms of space and stability requirements with some sacrifice in finesse. In the partial table below, the term d/r is 1 for the confocal spacing. Where the mirror RoC is 1 meter as with the Hi Res SFPIs, d/r then becomes the actual mirror spacing (though the actual RoC may differ from the spec and your mileage may vary). Using a lower value will permit the SFPI to be shorter, but the finesse also decreases. "Relative" is with respect to the confocal spacing. Here are the first 10 spacings which may be useful. There are also spacings that are longer than the confocal which may be useful for the 4.2 cm RoC mirrors, more info below.


Two example mirror RoCs are shown: 4.2 cm applies to the Basic, Deluxe, and Deluxe-Mini YOR 590-650 nm SFPIs; 100 cm applies to the Hi Res and Deluxe and Deluxe+ Hi Res and Hi Res SFPIs (both wavelength ranges). N=2 is confocal. N=3 is half-confocal with the advantage that it's FSR is 1/3rd larger which is beneficial for 633 nm HeNe lasers where the lasing bandwidth is 1.5-1.6 GHz.  For more information, see "Sam's Laser FAQ, chapter on "Laser Instruments and Applications", starting with "Scanning Fabry Perot Interferometers". Google will find it.

The mirror spacing for planar SFPIs is not restricted to specific values and determines the finesse by c/2L (c = speed of light, L= mirror spacing).  However, as noted, aligning planar SFPIs is much more challenging which is why planar SFPI kits include additional PZTs to be arrange around the periphery of the "holely" PZT for fine alignment which isn't essential but may make life easier.  Using them will require multiple variable voltage sources such as a 15 VDC power supply and potentiometers wired as voltage dividers (not included).

An electronic function generator with ramp or triangle waveforms may be used as a driver, or one can easily be built. An oscilloscope (almost any type) or data acquisition system (not included) will be required for the display.

The photo of the scan of a ~5 mW red HeNe is typical of what to expect with the Basic, Deluxe, and Mini-Deluxe YOR 590-650 nm kits.

For the Basic, Mini, Micro, Nano, and Selectable FSR 590-650 nm kits (Type 1-9), the Mini Laser Mode Analyzer (mLMA1) is an option to use in place of the scope and function generator, at least to get you started, though a real scope will still be better in the long run. mLMA1 is an Arduino-based system which replaces the ramp driver/function generator and oscilloscope. At present, it only provides basic functionality on a small screen including SFPI, MODE, and POWER functions (including dual polarization support with appropriate detectors in the head), but if you don't have access to test equipment, this may be acceptable. All parts are included except for a source of 5 V, which could be a USB port on a PC, laptop, a USB charger, a 5 VDC power supply, or backup USB battery (which has the lowest ripple and noise but may require an additional load to not shut down). The photos show the prototype electronic assembly displaying the modes of a short Zeeman HeNe laser tube and the PCB version displaying the welcome screen. That's it. Really! Cool, huh? ;-)  The mLMA1 kit includes the PCB and all other electronic components. The three-button interface/control panel is used to set parameters. But the firmware is public and documentation is on-line. So except for the PCB (which is quite simple), you can just do it on your own at much lower cost. Tech support may be a wee bit less friendly though. :) Search on the Web for "mLMA1 Mini Laser Mode Analyzer".

In my tests of one sample of the mirrors in SFPI YOR 590-650 nm kits, the reflectance was greater than 99.7% at 633 nm and the confocal finesse exceeded 500 which may actually surpass the performance of a $5,000 instrument. The finesse fell to around 250 at 594 nm (yellow HeNe), which is still quite exceptional. At 532 nm the finesse is very low, but still might be adequate to determine if a green laser is single longitudinal mode (single frequency) and suitable for holography. At 655 nm, the reflectance appears to be even higher than at 633 nm, possibly 99.9% or more, though greater finesse may be limited by other factors like coating losses and scatter. The reflectance is still around 99% at 680 nm for a finesse of 150. The performance above 680 nm is not known at this time, but the finesse should still be decent to 700 nm or more. However, I cannot guarantee that all mirrors will achieve these high finesses and careful attention to alignment (both of the mirrors in the SFPI frame and with respect to the laser) will be critical so your mileage may vary.

The finesse using the blue mirrors isn't that high, but is probably still sufficient to confirm single frequency/single longitudinal mode (SLM) operation of a laser intended for holography or interferometry.

All parts are new or like new. The PZT has been modified by drilling a hole in its center. And if that's all you want, buying just the modified PZT is an option also. You may even specify the approximately size of the desired hole. But the larger the hole, the lower the sensitivity of the PZT to the driving voltage. The default is 4-6 mm.

If there is a configuration that isn't here using any of the mirrors in this listing or any mirrors from my other listings, ask. For example, if adjustable mounts at both ends of the Deluxe or Deluxe+ SFPIs would be preferred, that can be arranged at just above the cost from Thorlabs (currently around net $85 since one cage plate is no longer needed). That's silly for the 4.3 cm RoC mirrors, but might make sense for the longer ones, especially the HiRes versions, and simplify the fabrication. Or leveling adjustments. Or longer or shorter cage rods. Or if you want the highest finesse possible using a 1+ meter frame for one of the Hi Res SFPIs, that can probably be arranged. ;-)

Much more information on SFPIs may be found in "Sam's Laser FAQ", chapter on "Laser Instruments and Applications". Construction guidelines specific to the parts in these kits may be found at "Sam's Electronics and Laser Kit Information and Manuals" in the Laser FAQ table of contents. A search engine will find these since eBay makes it impossible to provide useful information in listings. And lifetime (yours or the SFPI) email tech support will be provided.

The following options are also available (not covered by the selections above):
  • Set of adjustable front and rear mounting plates cut to size and rough-finished (translation: may be ugly), with adjustment screws to attach to the Thorlabs KC1 and front cage plate for deluxe kits that do not include them by default.  These are typically around 4x3/4x3/8 and 2x3/4x3/8 inches and provide height adjustments when the SFPI head is set on a table top.  Not required if the SFPI head will be mounted in some other way.  $25 additional.
  • Iris diaphragm that screws onto front cage plate as an aid in alignment and minimizing back-reflections.  $75 additional.
  • Blank ramp generator and preamp PCB: Up to 60 p-p triangle or sawtooth, variable frequency, amplitude, and offset. Also includes variable gain transimpedance photodiode preamp. A schematic and parts list will be provided. Uses all common through-hole parts available from any electronics distributor. The photo shows a completed sample. BLANK PCB ONLY is $25 additional.



  • Dual polarization blank PCB: This has a dual channel trans-impedance variable gain preamp with other features useful for the dual polarization option is also available but has NOT been fully tested. The photo shows a populated PCB. BLANK PCB ONLY is $30 additional.


Inquire for any of these or other options that may be available.  SFPIs can be configured with any suitable mirrors from my other listings or mirrors of your own.

If you have no idea what any of this stuff is, I can pretty much guarantee you don't need one or a dozen. Although the mirrors do make decent fish tank stones, there are much cheaper alternatives. ;-)

Due to the sensitivity of high quality laser cavity mirrors to abuse, there will be a 20 percent restocking fee if returned for any reason other than incorrect parts sent unless the sealed mirror package has not been opened, sorry.

The non-Deluxe SFPI kits (mirrors, PZT, photodiodes) will generally ship within 1 business day. But if Thorlabs parts need to be ordered for the Deluxe versions, the shipping time will be longer.

Thanks for looking!

--- sam