[UVC SAFETY WARNING] Microscopy at 254nm - build and images

[Andy Perrin]

Alas, I think I disproved my Newton ring hypothesis. This is what the radial distribution of the rings looks like, and the vertical lines are where the Newton rings SHOULD be. They don’t align well at all. The lines should be going through the peaks.

 

 

 

NEW THOUGHT: could you be seeing an Airy diffraction pattern from the light going through a pinhole somewhere?

https://en.wikipedia.org/wiki/Airy_disk

 

[JMC]

Thanks for checking Andy. As I am feeling better now, unfortunately it means I am back to work with a load to catch up on, so further microscopy testing will have to wait for now. Not sure where there could be a pinhole in the system, but I will have a think. Next thing for me to try though will be to add some diffusion to the light source - this is a major difference between the lamp for 254nm and the other setup (which doesn't produce the rings).

[Andy Perrin]

Diffusion might help even if it’s not the cause of the problem because it randomizes the phase of the light, which tends to destroy any interference pattern, regardless of origin.

 

ETA: Possible plot twist? If I try regressing the wavelength from the Newton ring formula instead of assuming it's 254nm, it spits out 313nm and a very nice fit:

Is there any way that some 313nm light could be making its way into the results?

[JMC]

UPDATE

It's been a year since the last post on here, and work on this build has been slower than hoped.

 

My monochrome d850 was able to image at 254nm, but exposure times were really long, and I had no way of focusing with live view as it was not sensitive enough. Also the fused silica window which had been used to cove the sensor had loads of very visible marks. Dan at MaxMax said that this is not unusual and the fused silica he uses has more issues than the WG280 he'd normally use for his conversions. For normal photography this is less of an issue, and with mine it only became a huge issue when using it for the microscope (with the tiny 'f stop' of the lenses). I've now had the d850 window put back to Schott WG280 which means I cannot use it below 300nm, but it is great for 313nm imaging.

 

I bought a Matrix Vision machine vision camera with the UV sensitive Sony IMX487 chip, and with that I was able to get images at 254nm in seconds rather than minutes, and it allowed me to focus. Bit of a writeup here - https://jmcscientificconsulting.com/mini-uv-camera-initial-diatom-images-using-254nm-light/

 

However I still had issues with rings in the 254nm images, and now I had vertical banding if I used high gain on the machine vision camera. The horizontal bands were associated with high gain, and ideally I don't want to be using high gain anyway, so while these are a concern, they're not my biggest problem.

 

That was at the end of last year, and I put the project to sleep for a while to have a think.

 

The 3W mercury xenon lamp I was using gave a nice sharp 254nm peak, but still needed optical filtration for imaging, even with the highly sensitive UV camera. Also, it gives out light at 360degree and putting a lens next to it still only captured a small amount of light. Ideally I needed a focusable UVC light source. Early this year I invested in a Thorlabs deuterium lamp, as I could use it for this as well my as a source for spectroscopy. Initial testing was promising, although peak power was well down on the 3W mercury xenon lamp at 254nm which was disappointing.

 

This got me wondering if a broad band UVC filter, letting through plenty of light between 250nm and 300nm might be the way to go, in combination with the deuterium lamp. I approached Asahi about their XUV0310 filter. This was March and I was told they'd be ready some time in May. This ended up being the end of June. I bought one which turned up recently, and this in combination with the deuterium source should give quite a bit of light. Whether it is enough remains to be seen (literally).

 

Work on it is on hold at the moment. To do UVC experiments I need to make some modifications to my imaging system, and while I am working with it regularly I don't have the time.

 

By the way, that little 3W mercury xenon lamp, which I was running on 10V DC is apparently supposed to be used with AC (although it will work with DC). Guess what, the information I got from the seller was incorrect. Who'd have thought it.....

 

Anyway, a bit of rambling thread, and I hope to return to this again when i get the time and the passion for it.

[colinbm]

@JMC what deuterium lamp are you using, model number & watts please ?

[JMC]

1 hour ago, colinbm said:

@JMC what deuterium lamp are you using, model number & watts please ?

Thorlabs SLS204, 30w - https://www.thorlabs.com/thorproduct.cfm?partnumber=SLS204

 

I wouldn't rush out and buy one for UVC one just yet though. I still think the mercury lamps with a good strong 254nm line are a good option for general UVC imaging. Deuterium lamps give a broader emission, but not as intense.

[colinbm]

2 minutes ago, JMC said:

Thorlabs SLS204, 30w - https://www.thorlabs.com/thorproduct.cfm?partnumber=SLS204

 

I wouldn't rush out and buy one for UVC one just yet though. I still think the mercury lamps with a good strong 254nm line are a good option for general UVC imaging. Deuterium lamps give a broader emission, but not as intense.

Yes, Thanks, Jonathan, that is why I asked.

[JMC]

1 hour ago, colinbm said:

Yes, Thanks, Jonathan, that is why I asked.

No problem Col.

[dabateman]

The spectrum for that instrument is interesting:

 

I usually see a filter or cut-off at 350nm/400nm for these bulbs in the instrument. 

 

Jonathan,  are you using it as a free light with the fiber optic removed and the 30mm cage?

[JMC]

14 hours ago, dabateman said:

Jonathan,  are you using it as a free light with the fiber optic removed and the 30mm cage?

 

I remove the fiber optic connector and just screw an SM1 tube into the front (with a fused silica condenser lens to try and roughly collimate the beam). I've not bothered with the 30mm cage setup as I need to get the SM1 tube inside where the light goes into the microscope.