Optomechanics – SOLVED: Elastic Theory’s Differential Equations for the Tensile Stresses in Glass Lenses Mounted in Threaded Metal Rings


AEH has solved elastic theory’s differential equations for the tensile stresses in glass lenses mounted in threaded metal rings, and it’s good news.

Paul Yoder had originally proposed Delgado and Hallinan’s 1975 solution (Opt. Eng. 14) but their solution gave very high tensile stresses in the lenses, high enough that virtually all such lenses should have fractured.  None of my ring mounted glass lenses had ever suffered that fate.  I surveyed a number of my colleagues and none of them recalled a ring mounted glass lens fracture.

Delgado and Hallinan’s work was flawed.  To correct their flaw would require a new solution to the equations of elasticity that honored the appropriate contact geometry.  AEH finally made it happen and the result is surprisingly simple,

s = p(1-2u)/b,

where s is the peak tensile stress, p is the linear ring load, b is the radius of the contact ring and u is the Poisson’s ratio of the glass.  This stress is three-to-four orders of magnitude lower than that predicted by Delgado and Hallinan.

Using Nastran AEH was also able to verify the general shape of the stress distribution in spite of Nastran’s notorious difficulty at the point of load application.

Closed-form solution       >>>         Nastran solution

To learn more you have choices:  Either download AEH’s peer reviewed paper from SPIE [Optical Engineering 57(5), 055105] or go through the gory details with me in my tutorial,

“Optomechanical Analysis,”
SPIE’s Optics and Photonics Symposium in San Diego
8:30 AM to 5:00 PM on the 21st of August.Cheers!

Al H.

Optomechanics – Quick Checks for Stress in Glass


Well, Ok.  It’s not that AEH hasn’t seen broken glass this past year, it’s just that it hasn’t been AEH’s glass that broke.  Cemented doublets were the principal excitement.  AEH’s research indicates that, for a quick check,

tensile stress in the glass =~ (E1 + E2)/2 x (alpha1 – alpha2) x deltaT


shear stress in the adhesive =~ 2/3 x tensile stress in the glass.

If stresses are marginal the engineer may then want to adjust for the edge thicknesses of the lenses and the Poisson’s ratios of their glasses.  The peak shear and tensile stresses occur at or near the edges of the lenses.  The only dimensions that influence the stresses are the edge thicknesses.  Center thickness and diameter have little influence on the stresses at the edges.

  Radial Tension                             Shear                                 Axial Tension

Does it all seem spooky?  Well, I’ll take you through the gory details in my tutorial,

“Optomechanical Analysis,”
August 21st in San Diego at SPIE’s Optics and Photonics Symposium.

And, I’ll toss in, just for you, the latest details on the stresses in ring-mounted glass lenses including a close-form solution and a finite element simulation!

I’ll see you all in San Diego.  Bring your sun-screen. Al H.

Optomechanics – The Industry Needs to Know the Strength of Optical Glasses


Fall is coming in two weeks and the Great Pumpkin is right down the road.  It’s time to kick-back and just look around a bit at this Glorious Summertime…

I’ve had about four weeks on the road lately, touching base with all of you (or most of you, I hope).  Then I cruised around SoCal in my spare time chinning and jawboning with the local industries’ participants.  So, what are the “hot items” for optomechanical engineers today?  Well, how ’bout…

precision dimensioning and tolerancing of optical structures
repeatability and stability of instrument performance
broken optical glass

I’d have trouble identifying the most important of these, it all depends upon what’s happening NOW.  All three of these have kept me pretty busy since Valentine’s Day.  The greatest uncertainty for the engineer, however, is in the strength of optical glasses.  Its not just mirrors and windows. 

I’ve participated in two projects in which the optical design had to be revised (compromising performance) to replace glasses that could not pass the environmental tests.  Perhaps, someday, the glass houses will start to provide strength information on their data sheets near the Young’s modulus and Poison’s ratio.  Today the engineer can’t be sure until the tests are passed.

And we, all of us, managed to squeeze-in a terrific conference with SPIE in San Diego last month (32 papers published).  How we were able to pull that together, I just don’t know.  But, it would never have happened without you and the terrific staff at SPIE who keep us on the right track.

Here comes Guy Fawkes Day. Get your bonfires, and marshmallows, ready! All our prayers this day are with those who may be in harm’s way.

Al H.

Optomechanics – Using CodeV Prescription in Ivory and Jade to Find Structural and Thermal Weaknesses


I’ve been known to lecture my students and colleagues on the need to keep their tools sharp.  Some time ago AEH was invited to a design review as an observer and since I had no direct participation I sat at the back of the room, behind John, the systems engineer who was controlling the projector.  The technical sessions went well but about half-way through the schedule and budget sessions he suddenly blackened the screen and turned on the overhead lights.  He slowly turned and surveyed those of us sitting behind him.  His gaze settled on me!  “What, John?” I asked.  He stared at my hands which were holding my pen knife and its sharpening steel.  “Just keeping my tools sharp,” I declared sheepishly.

One of AEH’s sharpest tools, other than a pen knife, is Ivory’s Optomechanical Modeling Tools.  It’s been under continuous development incorporating many of my personal insights working as a mechanical engineer in the optics industry.  I recently put together an updated version and released it to all users of Version 3.  That’s another way I keep AEH’s tools sharp (and protect AEH’s Ivory subscribers, too).  Ivory is AEH’s prime tool for engineering thermally and structurally reliable optical systems.  It’s designed to work in both Excel and Nastran and its application early in the design process prevents much embarrassment and saves many labor-hours from preventable failures that may occur later in qualification tests and service.

Somewhat more recently AEH was invited to participate in a “Tiger-Team” review of a sub-contractor.  The initial issue was broken glass.  The first thing I did was get a copy of the physical optical prescription (CodeV) and read it into Ivory (for the structure) and Jade (for the broken glass).  I could then quantitatively infer where the principal structural and thermal weaknesses might be.  With that insight I was able to form an independent assessment of the completeness of the design team’s engineering effort, which undergirded my report to the prime contractor.

I hope to see all of you at SPIE’s Optics+Photonics in San Diego come August.  I’ll be teaching (Optomechanical Analysis), chairing (The Optomechanical Engineering Technical Group and Optomechanics 2017), presenting and publishing (on a new diffraction grating capability in Ivory) and begin planning our next SPIE Conference (Optomechanics 2019). 

That also keeps AEH’s tools sharp. 

Hasta luego, caiman.

Al H.

Optomechanics – SPIE


Well, the weather’s warming up here in SoCal.  The beach and surf await us all.

SPIE’s annual gathering in San Diego awaits us as well.  I’ll chair an evening meeting of the International Technical Group of Optomechanical Engineers (8 to 10 PM on August 30th).  Professor Tony Hull (UNM) will be our feature speaker.  He’ll discuss the recent advances in light-weight glass-ceramic mirrors for space (and other) missions.  And there’ll be Conferences, Equipment Exhibits, Tutorial Classes, Evening Receptions, the Grand Awards Banquet and great camaraderie.

Don’t forget to visit SPIE’s book display near the registration area.  There you’ll be able to leaf-through a copy of my new book, The Optomechanical Constraint Equations:  Theory and Applications.  I have bared all of Ivory’s secrets in this tome.  If you visit the SPIE Publications website:


you’ll get a quick glimpse of what you’ll find in the book.

And for the surfer-dudes among us the beach and the blue waves will be only a ferry-ride away.

I look forward to seeing you all in San Diego:  Hopefully, nearer the books than the breakers!

Hasta luego, caiman!

Al H.

Optomechanics – SPIE in 2016


Joy to the World!

While we wrap-up a glorious 2015 with parties and presents we should pause to recognize that the end of the year is not the end.  Rather, we look forward to a new beginning in a New Year, 2016.

Two events in 2016 require the immediate attention of optomechanical engineers and they are both conferences in San Diego during SPIE’s Optics+Photonics Symposium.

The first conference is “Optical Modeling and Performance Prediction VIII,” and is chaired by Mark Kahan of Synopsis Inc. and Marie Levine-West of JPL.  Real performance predictions are not possible without coupling the mechanical behavior to the optical surfaces, materials and elements.  Optomechanical engineering is central in assuring the desired performance in the final design and we make valuable contributions here.

The second conference is “An Optical Believe It or Not:  Key Lessons Learned V.”  This conference is also chaired by Mark Kahan and is unique in that it encourages engineers to share with colleagues what they have learned from their experiences, and other people’s experiences too.  Identities, individual and corporate, may be protected (shrouded by whatever means are considered appropriate by the speaker), encouraging discussions of problems and solutions without casting blame and damaging reputations.

The immediacy mentioned above is imposed by the due date for abstracts, February 8, 2016.  That may sound like a long time away, but with the Holidays and the New Year crank-up activity the time will slip away from us quickly and many days can be lost waiting for approvals.

The details of each conference are attached.  So plan to get your abstracts in early. 

Then, Have a terrific Holiday Season.

Al H.

Optomechanics – A Unified Optomechanical Model


The end of summer was a crazy time.  Whew!

On my return from our San Diego meeting I helped develop the structural design for a new optical system.  That seemed more important, at the time, than a biennial, “Thank you,” in a newsletter.  Optics had to stake its claim for structural resources (stiffness) competing with the other disciplines.  A Unified optomechanical model was the method.

We got it and the initial concept meets the specifications now.  So…

Now… I can take a moment to thank all of you for making this year’s gathering in San Diego, of the International Technical Group on Optomechanical Engineering, a resounding success:  Thirty-two published papers in a two-day conference, two outstanding invited speakers (one on optical tolerancing, one on readiness assessments) and an evening meeting on ground-based testing of space-based optical systems.  SPIE’s Optics+Photonics Symposium was the perfect host.  They and I look forward to organizing a similar event in two years, 2017, and we expect to see you all there one more time.

Thank you, thank you and thank you, my colleagues.  I apologize for having ignored you all these weeks. 

All is well at AEH and Autumn is safely here now.

School has started, the parents are on the loose again…

…and The Great Goblin awaits!!!

‘Tis time to keep your tools sharp!

Al H.

Optomechanics – Bad Behavior in Complex Systems


One of the challenges for a mechanical engineer is to determine the dominant drivers of bad behavior in complex systems.  The behavior may be observed during service, in environmental tests or system analyses.

In optical systems AEH segregates the effects of each degree of freedom (Tx, Ty, Tz, Rx, Ry, Rz) of each optical element (1, 2, 3, …, detector) and plots the cumulative sum which, in the case below, exposes the major offending elements to be 1 and 5 (see chart).  The engineer may then objectively recommend structural design changes that will stabilize the offending optical elements and improve the optical performance of the structure.

I’ll be presenting the details of this approach in a paper during SPIE’s Optics+Photonics Symposium in San Diego this August.  I hope to see you all there.

In the meantime, if you have questions just give me a call.  I’ll be here.

Happy St. Patty’s Day.

N’Blarney ‘ere, b’Gorah!

Al H.

Optomechanics – SPIE


Summer’s coming, and so is SPIE’s magnificent Optics+Photonics Symposium in San Diego, August 17th through the 21st.  The week will be loaded with optomechanical events and technologies.

On Monday the 18th I’ll be presenting a paper, “Use It Or Lose It,” in Mark Kahan’s conference, “An Optical Believe-It-Or-Not:  Key Lessons Learned III.”  That should be a hoot! 

Then, Bright and early Tuesday, the 19th, there’s a meeting with SPIE staff for planning next year’s Optomechanical Engineering Conference.  That conference will be your place in the sun, technologically speaking, so get your abstracts ready for submittal and spread the word to your friends and associates.

Tuesday evening, 8 to 10 PM, the Optomechanical Engineering Technical Group will hold their annual West Coast Bash.  Our speaker will be Tony Hull, Adjunct Professor of Astronomy and Astrophysics at the University of New Mexico.  He’ll be addressing the primary mirror material selection process for spaceborne telescopes and how it drives the architecture and planning of these systems. 

Wednesday, the 20th,I’ll be teaching my tutorial, “Optomechanical Analysis,” all day to a bunch of bright-eyed students.  This is aimed primarily at mechanical engineers and I try to give them some new tools to relate their mechanical engineering decisions to the optical behavior of their systems.  This material may also be of interest to other optics professionals, even structural engineers.

Wednesday evening is SPIE’s Awards Banquet where all of the elephants of the academy and industry gather to celebrate new honorees.  This is always a great event and I’m sure that Phil Stahl, our President, will put his usual high gloss finish on the whole program.  I may be weary from teaching all day but this is always a must-do event for me.

And Thursday, ahh… Thursday:  Finally, I’ll get to cruise the exhibits, mingle with colleagues, meet new people, and catch up on the technology in the conference rooms.  Then at the end of the day, after the exhibits close, a few of us will go out to a local bistro for a toast-n-roast dinner (maybe with some red meat, even!).

It’s all one great week-long event:  More material than you can ever hope to capture in real-time.

And I hope to see you all there.

Al H.

Optomechanics – SPIE


On the evening of May 6th, during SPIE’s Defens+Security+Sensors Symposium, I’ll be hosting a meeting of the Optomechanical/Instrument Technical Group.

Our speaker will be Steve Rummel, Director of Product Technology for II-VI Infrared of Saxonburg, PA.  II-VI is a major supplier of optics for CO2 laser applications.  Mr. Rummel will discuss new developments in highly stable, heat resistant materials for use in high power applications, especially where a high quality optical finish is required on the surfaces.  He’ll review the microstructure and property data II-VI’s reaction bonded silicon carbide, discuss diamond-containing formulations for ultra-high heat load capability and present B4C containing versions which compete with beryllium.

This is the East Coast meeting of the premier group of optomechanical engineers that design and analyze the world’s optical instruments and systems. This gathering is open to all attendees to the Defense+Security+Sensing Symposium. Anyone who wishes to put an item on the agenda should contact the Chair, Al Hatheway, at aeh@aehinc.com.

The meeting will be from 8 to 10 PM in the Hilton Hotel associated with the Baltimore Convention Center.  Check the Symposium Program or the registration desk for the room’s location.

The Baltimore DSS Symposium is a terrific gathering of the technologists that “make it all happen.”  It’s only two months away.  Set the time aside now, you’ll be glad you did.

I look forward to seeing you all there.

Al H.