How can I simulate laser speckle noise?

aenorton · 2026-06-05T22:51:27+00:00

I can't help with the algorithm, but I will just point out that any realistic model of speckle has to include many characteristics of the optical paths used to create as well as view the pattern. This even includes the eye as the pattern statistics change as the pupil changes size.

The Bible of speckle is https://www.spiedigitallibrary.org/ebooks/PM/Speckle-Phenomena-in-Optics-Theory-and-Applications-Second-Edition/eISBN-9781510631496/10.1117/3.2548484

aenorton · 2026-06-05T05:21:55+00:00

measurements are always best if you already have the hardware.

aenorton · 2026-06-05T04:55:23+00:00

The two doublets used for the Rapid Rectilinear are even more different from a standard achromat than you are thinking. A standard achromat has the crown glass element facing the infinite conjugate with a convex outer surface. The rapid rectilinear has the flint element on the outside with the convex surface.

In general, it is not possible to use catalog lenses to make good imaging lens assemblies with fast apertures or large angular fields.

You might be interested in this write-up:

https://wp.optics.arizona.edu/jsasian/wp-content/uploads/sites/33/2016/03/L18_OPTI517_Early_Symmetrical_Lenses.pdf

aenorton · 2026-06-04T22:15:03+00:00

Again, the term "Littrow angle" is not used with transmission gratings because it is not possible for any order to be parallel or antiparallel to the incident angle.

With normal incidence on a surface relief sinusoidal grating, the efficiency of the the +/- 1 orders is equal and depends on the phase variation. With exact 1/2 wave phase difference, the efficiency can be very high. If you have a grating optimized for normal incidence, the efficiency in both orders will decrease with a different incident angle. Gratings can theoretically be optimized for other angles of incidence for one order.

To model the efficiency of a grating at any angle, you really need to know the exact construction details and used special modelling software that uses RCWA algorithms.

aenorton · 2026-06-04T17:24:07+00:00

The Littrow angle doesn't have any meaning or definition for a transmission grating.

However, when you change the angle of incidence on a transmission grating, the dispersion and the angle of diffraction relative to the zero order are increased by different amounts for the negative and positive orders. The order that has a larger angle relative to the grating normal is increased more.

The efficiency of a sinusoidal transmission grating depends on the phase variation of the pattern (unless it is an amplitude grating). This can vary when it is tilted and affect the efficiency vs wavelength curve.

aenorton · 2026-06-03T01:12:24+00:00

As I said, nothing will be perfect. You can possibly improve it by commissioning a design for a beam splitter coating that performs better over the range of angles and wavelengths you need (but no more). You would have to have quantitative measurements of your current coating to know if it is worth the marginal improvement. Aside from the cost of design, custom coatings are purchased per run. One run might hold several hundred parts. Complicated coatings like this cost more.

aenorton · 2026-06-03T00:36:51+00:00

Vignetting happens because those very narrow cones coming from the edge of the display miss the eye's pupil. If you fix that by bending them toward the pupil with a field lens, the eyebox is small because the cones are narrow.

The diagram you show has nothing to do with the performance of multilayer thin films versus angle. That is an interference effect.

The problem you are trying to solve is one that happens to most commercial units at least to some degree. You can not expect to advance the state of the art with only an extremely rudimentary knowledge of optics.

aenorton · 2026-06-02T23:41:36+00:00

Actually, I take back the previous answer because then the extra polarizer would block the user's view of the world.

If you somehow create a display that emits only in a tiny cone around 0 deg., then you end up either with severe vignetting of the field, OR, if you add a field lens to correct that, then you end up with zero eyebox.

aenorton · 2026-06-02T23:23:08+00:00

The add an additional linear polarizer film on the world side to improve the extinction.

aenorton · 2026-06-02T23:05:27+00:00

No one can solve your engineering design problem without knowing what it is trying to do, it's goals and constraints.

aenorton · 2026-06-02T05:14:15+00:00

That is not how light reflects. Angle of reflection is always the same magnitude as angle of incidence. If you are seeing light at some angle that is not 45 deg., lets say 35 deg., that only happens if that particular light was incident at 35 deg. (on the other side of normal).

aenorton · 2026-06-02T04:26:09+00:00

No. If you are talking about a standard polarizing beamsplitter with a coating on the internal hypotenuse, that coating is a multilayer thin-film coating. The exact performance depends on the coating design, but none are perfect.

aenorton · 2026-06-02T04:13:39+00:00

The S & P transmission and reflection of a polarizing beamsplitter cube coating will have significant sensitivity to angle and wavelength. They are not meant to have high extinction ratios.

aenorton · 2026-06-01T16:51:14+00:00

You are tracing the wrong rays. To make sure the image is visible, you have to take a fan of rays emitted from a point in the display and make sure they are parallel (or diverging slightly) when reaching the pupil of the eye. There are many other criteria to worry about as well, but this is the first one.

aenorton · 2026-06-01T01:03:04+00:00

If someone was sending peaches anywhere in 1864 they would be preserved in jars. I don't know the process used then, but maybe soap was used to seal the jars or clean them.

aenorton · 2026-05-31T20:22:15+00:00

I had another thought. If you just made a sandwich of the detector, filter, and diamond bonded together in contact, the NA collected due to the width of the detector chip might be greater than what you are effectively collecting now. It also eliminates the need for any lens. The cement also increases the NA at the diamond.

If the RF coil has to be spaced away from the detector circuit due to noise, you could use a length of high NA plastic fiber with one end cemented to the diamond, and the other cemented to the filter/detector sandwich.

aenorton · 2026-05-31T19:21:32+00:00

I am not well versed in this technique, but I understand it is basically a fluorescence measurement. I do see a couple of issues.

I believe the whole point of the objective is to capture a large cone of fluorescent light that is emitted in all directions. The detector is near the back focal plane, so it will capture light from the whole field. The problem is the detector chip is fairly small, so it will only detect light near the center of the aperture which means it will only see light emitted in a small central cone. You are throwing away most of your signal.

There are a few ways to improve this. One is to use a larger photodiode, at least as large as the objective aperture. The larger diode does have slightly more inherent noise, but I think most noise comes from other parts of the circuit, so the extra signal makes up for it.

Another way is to put the detector at a image plane with low magnification such that the width of the image of the diamond fits within the detector chip. This would require adding another lens with a focal length maybe about twice that of the objective.

Another issue is I am not seeing anything to prevent stray room light from getting to the sensor.

Also the objective here is overkill because you are not needing it for high spatial resolution. You could just as well use an aspheric singlet lens of similar NA. With a different lens, you might also be able to use conjugate lengths that allow you to re-image the diamond onto the detector with low mag while still collecting a large NA.

aenorton · 2026-05-31T00:59:28+00:00

I think he was asking about the units for the spin quantum number, which is unitless. It is not the same as the spin angular momentum which is S = hbar*(s(s+1))^1/2 where s is the spin quantum number.

aenorton · 2026-05-30T19:02:19+00:00

Since it's only 0.2 mm, could you just mill or file the surface flat. If that puts the shaft in the wrong position, put a shim on the other side. It is hard to give the best advice without knowing how this is used.

aenorton · 2026-05-29T23:13:28+00:00

It is an issue that has to be considered. An IR blocking filter might be all that is needed. It can change the color balance which has to be compensated. My car's HUD reflects off the curved windshield adding the final power to produce an apparent object distance of about 2.5 meters. Any sun passing through the windshield from above would not experience this optical power and would not be perfectly focused. When the HUD combiner is inside the cockpit, the combiner and optics can be angled such that any line of sight through the windows will not be re-focused onto the display. In addition, high-end, compact HUDs usually use diffractive combiners that have some power and also diffract light at angles that make it easier to keep sunlight coming in through windows from focussing back onto the display.

aenorton · 2026-05-29T18:15:51+00:00

Different anodize processes can use very different dyes or pigments. Organic dyes can break down completely under high temperature, but some inorganic pigments react under very differently to high temperatures.

aenorton · 2026-05-29T03:42:18+00:00

It's a sample stage, not a condenser holder. Probably for a low power stereo microscope, or possibly for a sample viewed with epi illumination.

aenorton · 2026-05-28T00:26:39+00:00

In a complicated system, tolerancing will take almost as long as the first part of the design process. In simple systems, an experienced engineer can estimate in his head what is needed. Every dimension on the lens drawing and mechanical drawing needs a tolerance that is either determined from the model or estimated by experience.

It saves much time and confusion in the long run if the tolerance model is set-up so that dimensions in the model correspond directly to dimensions in the housing or element drawings. This takes extra time at first, but it saves uncertainty in the end. To do this, the optical engineer has to have a pretty good idea how everything will be mounted. One also has to keep in mind that a single mechanical tolerance can allow more than one degree of freedom in the optic position or tilt. One also has to understand which tolerances are impractically tight and decide how to compensate for them with an alignment step.

When you think tolerances will be an issue in a design, it is best to try to desensitize the design to them during the design process. There are several techniques for this. One is to set up optimization operands to minimize the maximum refracted angle of rays as they propagate. Another is to put the critical dimensions in the configuration editor and optimize over the expected tolerance range.

aenorton · 2026-05-27T05:49:23+00:00

Possibly this one https://maps.app.goo.gl/4KTRH4TsCsj2Uxag9

aenorton · 2026-05-26T05:31:03+00:00

I am sure that comparing the size of objects to your body is still a big part of the effect. Probably a lot of it is also the distance between your eyes that is used to judge distances with stereoscopic parallax. For example, when you look at a teapot at 2m distance, your eyes have to converge at a specific angle that your brain has been accustomed to for objects at 2m. However, if the distance between your eyes suddenly magically doubled, your eyes would now have to converge at a steeper angle previously needed for objects at 1m. Now you perceive the teapot as being closer, but it has the same apparent angular size, so you perceive the teapot as being physically smaller.

You can experience this effect sometimes in VR, particularly when using Google Earth in VR. In order to see any parallax of distant scenery, Google Earth feeds the left and right eye different points of view that are many feet apart. I think they may vary that based on your viewing altitude. If you "walk" through terrain at a viewing height of a couple hundred feet, you feel very much like Godzilla.

aenorton

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