
World’s Shortest Wavelength Laser Diode Emits Deep UV Light at Room Temperature - bookofjoe
https://iopscience.iop.org/article/10.7567/1882-0786/ab50e0
======
rubidium
In the atomic research world, diode lasers are great because they’re cheap and
fairly tunable.

Many of atomic cooling studies done 20 years ago were done using rubidium
because it had a primary absorption wavelength that matched what commercial CD
players used. This made the 780nm diodes dirt cheap.

Having new wavelengths of diode lasers makes certain basic research more
accessible. I’ve been out of the field too long to know where this one may
help but it’s exciting to see progress.

~~~
fsh
Nowadays in atomic physics frequency-quadrupled diode lasers are commonly used
for accessing DUV wavelengths. They produce a lot of power and have narrow
linewidths, but are very expensive (>> 100k€). Here is a chart from one
manufacturer that shows commonly accessed transitions:
[https://www.toptica.com/fileadmin/Editors_English/15_downloa...](https://www.toptica.com/fileadmin/Editors_English/15_downloads/TOPTICA_Laser_Absorption_in_Physics_Chemistry_Biology.png)

In the paper the authors only demonstrate pulsed operation of a bare laser
diode. To make it usable for atomic physics, they would have to achieve
continuous-wave operation with feedback from an external cavity. This might be
pretty difficult to do.

------
Zenst
This is good, the usage for UV is huge and anything that reduces costs will
only help.

Whilst many don't need it, I'm sure having a UV filter of your water would not
go amiss.

~~~
m-p-3
Or maybe for photolithography hobbyist.

~~~
jjoonathan
Yeah, especially because that hinges on having coherent light, whereas
sterilization does not AFAIK.

As for incoherent UV light, I wonder how this laser compares in efficiency to
arc lamps. Is that still how incoherent UV is generated? Deuterium and mercury
vapor? Or have LEDs taken over?

~~~
fsh
DUV for lithography is usually produced with excimer lasers at 248 or 193 nm.
While they are technically lasers, they are barely coherent and have horrible
beam quality.

For other applications such as sterilization or curing adhesives, mercury
vapor lamps and LEDs are popular.

------
howardD
Normally, in LEDs and solid state lasers, there is a direct relation between
wavelength(energy quantum) (electron-Volts) and operating voltage (Volts).

For example Red = 660 nanometers = 1.8 electron-Volts = 1.8 Volts, which is
the typical operating voltage for a Red LED.

Blue = 470 nm = 3.3 eV = 3.3 Volts operating voltage.

So: Deep UV (270 nm) is supposed to operate on ~4.6 Volts.

But article mentions 13.8 Volts. I wonder why there is such a huge gap?

~~~
fsh
The bands of laser diodes are not necessarily sharp, so there can be a
significant difference between the injection voltage and the photon energy.
The paper mentions that their particular doping method produces a step-less
valence band profile.

Furthermore, they need a fairly large current (0.4 A) to get this thing to
lase. The "knee" in the U-I curve is at around 9 V and 0.05 A, so there seems
to be a fair bit of voltage drop due to internal resistance of the device.
This is probably also why they have to pulse the laser with a 0.01 % duty
cycle in order not to produce too much heat.

~~~
MayeulC
By sharp, do you mean a direct band-gap?

I recall that you sometimes want to pump your atoms in a higher energy state
than the one that corresponds to the output energy, but I forgot its
usefulness. Could someone enlighten me on this? Or is it just for optically
pumped mediums (thus pumped with higher energy photons than the emitted ones)?

~~~
fsh
It is impossible to achieve inversion (and therefore gain) by optically
pumping a medium exactly at the emission wavelength. Therefore, optically
pumped laser gain media are at least three (usually four) level systems.

------
api
Does this have any implication for chip fabs? Right now EUV requires crazy
Rube Goldberg machines using tin plasma or something like that, which is
insanely expensive.

~~~
hwillis
EUV is 20x smaller wavelength, 10000x higher power, and far larger area

------
rahimiali
it's noteworthy that even when it's on, this laser is mostly off. its duty
cycle is 0.00001% (50 ns at 2khz).

------
balaclava9
Who is the lead writer of this paper? According to google Ziyi Zhang is a
famous Chinese actress.

~~~
rubidium
Likely not the same person. From the article:

Author e-mails zhang.zc@om.asahi-kasei.co.jp Author affiliations 1 Innovative
Devices R&D Center, Corporate Research & Development, Asahi Kasei Corporation,
Fuji, Shizuoka 416-8501, Japan

2 Center for Integrated Research of Future Electronics, Institute of Materials
Research and System for Sustainability, Nagoya University, Furo-cho, Chikusa-
ku, Aichi 464-8601, Japan

------
xellisx
But can I use it to burn things?

~~~
dhabxkxbx
What does “Burn” mean?

Break the bonds of just about anything except fluorides and metals? Probably.

Deposit enough energy I locally heat the material above it’s auto ignition T?
Well that’s a flux question

~~~
dang
This looks like a great HN comment, but could you please stop creating
accounts for every few comments you post? We ban accounts that do that. This
is in the site guidelines:
[https://news.ycombinator.com/newsguidelines.html](https://news.ycombinator.com/newsguidelines.html).

HN is a community and we want it to remain one. For that, users need some
identity for others to relate to. Otherwise we may as well have no usernames
and no community, and that would be a different kind of forum.
[https://hn.algolia.com/?query=by:dang%20community%20identity...](https://hn.algolia.com/?query=by:dang%20community%20identity&sort=byDate&dateRange=all&type=comment&storyText=false&prefix&page=0)

You needn't use your real name, of course.

~~~
dhabxkxbx
“ This looks like a great HN comment, ”

Thank you. I thought it was rushed w/out the explanation that it deserves (it
has fascinating implications about the lack of the color blue in nature).
Also, I felt it came out as snarky or arrogant, which I didn’t intend. But I
was juggling other things :S

Unfortunately, I’m afraid you’ll have to ban me. I’ve abused the site far too
long but I also have no intention to expose myself w/ a profile (any user with
a karma > 1000 is trivial to dox).

~~~
deogeo
> any user with a karma > 1000 is trivial to dox

How so?

