a Poor man's allo-fluorescence

[iconoclastica]

I thought I might get surface shadows when in epi-mode I'd light the object with a laser beam from the side. I got no shadows, but the spores lit up brightly in the red laser light, reminding of fluorescent imagery. Pity you cannot see the glistening of the red stars, probably caused by my hand holding the laser pointer not too steadily. A Christmas card come early

Hard to see on the photos but clear in direct view: the spore walls seem to be clad with a network of mirroring elements, their lumina highly specular, the reticulum deep black.

The glistening is not (entirely) due to my shaking hand. After I wrote the above and forgot to hit the submit-button, I mounted the laser pointer on a tripod. The glistening continued, albeit seemingly more regular now. Also, there's a clear interference pattern over the whole image now:

laser mounted on tripod

I now could picture the netted surface:

detail of the image above (60x)

more detail (60x)

[rjlittlefield]

In your spore images, I notice that you are working at 60X, but nothing in the red pattern appears to be grossly out of focus.

This suggests to me that what you are seeing is almost entirely laser speckle, not a correspondingly fine structure of the subject.

See for example https://www.photomacrography.net/forum/ ... 14&t=16847 , and note my comment at the bottom of that post:

What's particularly interesting to me about these images is that due to the height of the inclined cover slip, I couldn't get the objective down low enough to focus so the subject is just a complete blur in normal light. I would show you the view, but basically there's nothing to see -- it's like looking at clouds through fog. What we're seeing here is entirely a speckle pattern, formed by the laser beam interfering with itself before and after reflection from the beetle. Sort of like a hologram, I guess, though I'm far from clear that it would be possible to reconstruct anything from a capture like this.

(Edited to add...)
I see that in a later post in the same thread I wrote:

When the lens is focused on the specimen, laser illumination is a disaster compared with conventional diffused incoherent illumination. At best I can still see structure of the specimen, but it is overlaid with a strong speckle pattern that makes it impossible to tell what's real texture and what is just speckle.

--Rik

[iconoclastica]

I never heard of 'laser speckle' before, but searching the web immediately produced much similar patterns. Still quite nice to see. I spent the better part of the day mixing it with transverse aand incident lighting but accidentally threw the photos away.

[Lou Jost]

You can get rid of the speckles and see the real subject textures by shining the laser pointer through a very dilute nearly transparent solution of milk. Generally this (or the equivalent) should always be done when illuminating with lasers.

viewtopic.php?f=8&t=36178&p=224498&hili ... lk#p224498

viewtopic.php?f=25&t=38802&p=243400&hil ... lk#p243400