Grimeton laser

This may be of some interest. I wonder how far away it can be seen? 

https://www.instagram.com/p/Ch9cQ8xtH5J/?igshid=MDJmNzVkMjY=

English translation below

Worldheritagegrimeton Light in the autumn darkness... What is it? Catch our green laser - and #tag your photos! Maybe you've never seen it? Maybe you have seen something and wondered? From the antenna tower of the world heritage site, the #artwork #Transmission glimpses from time to time. Green laser that sends secret (or loving) messages at Morse code intervals. The light that can be seen from several miles away conveys messages based on @UNESCO's work for peace and the equal value of people. Peace. Friendship. Freedom. Equality. Life. Love .... It was set up in 2020 by the light artist Aleksandra Stratimirovic and is a permanent work owned by the municipality of Varberg.  If you capture it on picture with your camera, don't forget to post your experience on social media, tagged with #transmissiongrimeton and @worldheritagegrimeton and we'll see your message! Who collects the most "transmission" spits during the fall. In a few days we will send the first one, and then three every month. If you still miss them all, you always have the chance at midnight on New Year's Eve! Photographer: Natalie Greppi # konstpålandbygd #konst #artwork #laser #greenlaser #Grimeton #artspotting #communication #morsecode # höstmörker # ljusimörkret # worldheritage #workdheritagegrimeton #UNESCO 

Laser information

In the past, I only tried 481THz (red light) transmissions with LEDs, but Peter Thornton G6NGR kindly sent me a useful link. There is lots of other interesting stuff on that website too.

See http://maxmcarter.com/lasrstuf/concentrator2.html

Commercial optical communications

Many years ago, before my stroke, I did some work at 481THz, red light. I used LEDs as the TX element, but I see that there are some commercial optical links using LASERS. Light has the advantage of being very secure. I expect these commercial units are expensive. My own optical kit was very inexpensive and great fun.

At some point I hope to get back to this work. Amateur optical work is both fun and inexpensive. It is certainly at the frontier of experimentation.

See http://www.lightpointe.com/laser-radios.html .
See https://sites.google.com/site/g3xbmqrp3/optical .

Optical DXing at around 460THz

Until I read the webpage below I didn't know that the record for optical morse DX goes back to 1896 and was an astounding distance of 183 miles using a Heliograph between Colorado and Utah in the USA. This link about the heliograph makes fascinating reading. The heliograph is essentially a keyed mirror that reflects sunlight and uses it to send morse code over long distances.  Modern versions of heliograph mirrors are available on eBay for emergency communications. See for example eBay item 250681260168. A good article about heliographs is on Wikipedia, see http://en.wikipedia.org/wiki/Heliograph.

Modern amateur optical DXing uses either lasers or high intensity LEDs. There is a piece about this on p51-52 of the Feb 2011 RSGB RadCom in Sam Jewell's "GHz Bands" column with further links including http://www.lasercomms.org.uk/index.htm which looks like a useful resource.  There was also a funny article in the RSGB Bulletin of April 1962 called "Getting Going on Bottom Band".  

Lightbeam communications

Before I became a radio ham, a friend and I had our first phone wireless QSO using a small torch bulb modulated with a couple of germanium transistors. The DX was across the road, about 20m at most. At the far end the receiver was based on an OC71 with its black coating scraped off, which made quite an effective photo transistor. These days there are much better ways. For some examples, see some of the fascinating links at  http://www.carolinaflashers.org/ . One of these days I must revisit optical communications. The picture on the right is from http://www.laud.no/ww2/lispr/index.htm and shows a WW2 lightbeam communications device used by the German Army.

Optical DXing - mirages

Andy Young has an excellent page about optical mirages which is worth reading. Land has been seen hundreds of kms over the horizon as a result of this phenomenon. Indeed there is some evidence that the discovery of Greenland may have been as a result of a mirage off the coast of Iceland. I'm not aware of radio amateurs exploiting fleeting mirages for optical frequency laser DXing.