Did someone put a curse on you?

I know the tweet is Al generated when they use " ," before and.

“I will NOT sacrifice the Oxford comma. We've made too many compromises already; too many retreats. They assimilate the em dash and we fall back. They capture ‘not just X but y’ and we fall back. Not again. The line must be drawn here! This far, no further!”

Presumably saying “everybody loves raiment”

Great work from @scrobarts.bsky.social!

Tagging for interest @captain1haddock.bsky.social @purpleswimbunny.bsky.social @jctravs.bsky.social @johnmdudley.bsky.social @fabiobiancalana.bsky.social @hwuphysics.bsky.social @eallan.bsky.social

Numerical simulations give specific outcomes; SCEM gives the entire possibility space. Congratulations to Seb for this amazing work, and thank you to @derryckreid.bsky.social for providing some historical data for comparison.

End 🧵

Top, the combined SCEM result for our chosen crystal and pump, showing SPDC, SHG, SFG and DFG outputs simultaneously. Bottom, the output from a numerical simulation showing strong agreement.

Spiderman pointing at himself meme, captioned "analytical SCEM" and "numerical simulation"

Final test: compare SCEM (top) to numerical simulations (bottom). Result? Excellent agreement!

12/

"Voltron" toy combining together from different components. The components read "SHG", "SFG", "DGF", and "Cascaded Interactions", and combine to give "full SCEM framework"

SCEM isn’t limited to SPDC. It generalizes naturally to SHG, SFG, higher-order QPM, and cascaded χ² processes, all combined on a common spectral basis. This is perfect for building full multi-stage interaction maps.

11/

Man tapping his head with a caption saying "compute once, reuse forever"

Nice bonus: you only need to compute the crystal-only efficiency map once for a given material. Store it, and then reuse it with any pump spectrum or system design. That means rapid exploration without new QPM calculations every time.

10/

Final SCEM for this combo of pump and crystal. The gain is not uniformly distributed, but is concentrated in key wavelength bands.

a meme saying "behold, the SCEM!"

Put it all together and we get the final SCEM. This reveals the true accessible gain regions for this pump–crystal combo.

The key insight: gain is not uniform across the SPDC band. Some regions dominate; others are weak despite being phase matched.

9/

Power conversion efficiency scaled by pump spectrum

"Epic handshake meme". The left arm reads "Intrinsic conversion efficiency". The right arm reads "pump spectral weighting". The combined hands read "full SCEM predictor map"

When we combine the intrinsic efficiency, the extrinsic intensity scaling, and crystal length we get the full SCEM prefactor map. This is everything except the phase matching term, and it sets realistic limits on conversion potential.

8/

Futurama "good news everyone" meme. The caption reads "the real pump profile gives us the actual SCEM weighting"

Then insert the actual measured pump spectrum. The real pump filters the gain landscape dramatically, highlighting which phasematched regions are fed with power.

7/

Power conversion efficiency of PPLN

"galaxy brain" meme. The small brain is captioned "using only sing-squared'. The normal brain is captioned "including prefactors". The galaxy brain is captioned "mapping the crystal power-conversion efficiency"

Now let’s add the intrinsic power-conversion efficiency. This shows which frequency pairs the crystal itself can efficiently convert, independent of the pump envelope - a major upgrade over pure sinc² models.

6/

Phase-matching curves using a top-hat pump instead of monochromatic. The broadband nature of the phase matching space starts to emerge.

Happy and sad views on a bus meme. Sad view is captioned "Monochromatic pump". Happy view is captioned "Broadband top-hat pump".

Next: switch to a broadband top-hat pump – now many pump wavelengths contribute simultaneously. The gain concentrates where QPM curves run steeply across the pump bandwidth – the first real “SCEM-like ” behaviour emerges.

5/

An image of the phase matching across many grating periods

Spongebob "old faithful" meme, captioned "Nonlinear optics community" and "monochromatic pump since-squared curves"

Let’s start simple, using a monochromatic pump and densely sampled grating periods. This reproduces conventional sinc² QPM curves, revealing a 2D gain map.

4/

An image of the parametric gain equation.

Charlie from "It's Always Sunny in Philadelphia" in front of his conspiracy board. Caption reads "It's more than just a sinc-squared term, I swear!"

At the heart of SCEM is the parametric gain. This includes two crucial prefactors that are often ignored: the extrinsic: crystal length and spectral intensities of pump/idler, and the intrinsic: material-dependent power-conversion efficiency.

3/

"Guy walking with his girlfriend getting distracted by a woman in a red dress" meme. The guy is tagged "nonlinear optics community"; the girlfriend is tagged "old sinc-squared monochromatic model"; the woman in the red dress is tagged "SCEM"

Standard sinc-squared QPM gain assumes a monochromatic pump & ignores frequency-dependent efficiency.

But real ultrafast systems use broadband pulses with complex spectra!

SCEM combines crystal properties and the real pump spectrum to map all possible conversion pathways in one picture.

2/

Leonardo Dicaprio meme where he's pointing at the TV. The caption says "Me seeing a new nonlinear optics technique"

PhD student Seb Robarts introduces Spectral-Crystal Efficiency Mapping (SCEM) – a new analytical tool for understanding broadband nonlinear conversion.

1/

New paper out in @physrevapplied.bsky.social!

If you use QPM crystals, OPOs, SPDC, or broadband pumps, this is very relevant.

doi.org/10.1103/bpxv...

Let’s dig in! 🧵

Fern Brady wearing a camera helmet on Taskmaster and opening the task, which has a red wax seal, and reading the contents. She has a purple set of coveralls on as well, which is just fun.

"Open the Strait of Hormuz. You may not receive the help of any other sovereign nation. Fastest wins."

This appalling fat cat wants to shut the door on all my mature students, many of whom left school after GCSE and give up a lot to go to university. I can tell him that they’re the hungriest for education and far from being unable to graduate, they regularly get the highest grades. Hateful man.

A picture of Heriot-Watt University's loch.

I prefer this one :)

I think about this Tony Benn speech much more than I used to

I think it’s a bot account…

what even is the fucking point

Isn’t that what Abstracts are for?

Researchfish — Information for Researchers Regarding Researchfish Sunsetting After careful consideration, Elsevier have made the difficult decision to sunset Researchfish on July 31st 2027, when the product will no longer be availab

OOOOH

Researchfish

Is going extinct 🐡🐟🐠

help.researchfish.com/en_US/resear...

Donate to Help me fund a month volunteering trip to Cambodia, organized by Daniel McCracken My school is partnered with Camps International to organise a mont… Daniel McCracken needs your support for Help me fund a month volunteering trip to Cambodia

My son is fundraising for a trip to Cambodia with Camps International, where they will help build schools, teach English and explore the rainforest. Donate if you can ❤️ #GoFundMe

gofund.me/fcec11da8

The application deadline of 30th January 2026 for the CDT in Applied Quantum Technologies is fast approaching.

We have up to 18 fully-funded PhD places across our three themes of Quantum Measurement and Sensing, Quantum Computing and Simulation and Quantum Communications.

Apply Now at aqt.ac.uk