Went on an excellent dive trip to the remote Rowley Shoals in Western Australia between 30/11/20-05/12/20 – Rowley shoals is about 300km northwest of Broome in Western Australia. Went with the dive boat the Great Escape The boat sets off from Broome and travels overnight to Rowley shoals. We encountered some rough seas and some of the passengers were seasick but arrived safely at our destination.
Day1
It’s a very remote location and the fish don’t get many visitors so they are curious about the SCUBA fish that blow bubbles. Check out this puffer fish.
I had the very annoying experience with my Atomic Cobalt 2 dive computer failing again after it had been “repaired” by Atomic. The Great Escape crew were excellent and quickly came up with a workaround. They lent me a simple pressure gauge.
Heres’ a white tipped reef shark resting on the sandy bottom and being cleaned
Day 2 of the great escape
Another view of a white tip
There were a lot of massive bump head parrot fish and reef sharks.
Day 3 & 4 of the great escape
A bump head getting cleaned by two cleaner wrasse
The eye of the clown fish
The coral rhino head
The dazzling smile and impressive, coral munching, teeth of the bumped parrot fish
The Clown fish don’t like to leave their anemone and so they are easy to photograph and video.
We headed back to Broome after the 4th day. We just missed a storm which arrived the day after we got back to Broome.
Authors:
Charlie Ironside,Department of Physics and Astronomy, Curtin University, Bentley, Western Australia
Bruno Romeira,Department of Nanophotonics, Ultrafast Bio- and Nanophotonics group,
INL – International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga s/n,
4715-330 Braga, Portugal
Jose´ Figueiredo,Department of Physics of the Faculty of Sciences at University of Lisbon, Campo Grande,
1740-016 Lisboa, Portugal
Morgan
Check out :-https://iopscience.iop.org/book/978-1-64327-744-8
The second edition of my book “Semiconductor Integrated Optics for Switching Light” has just been published (May 2021). Check out:-https://iopscience.iop.org/book/978-0-7503-3519-5 It’s a book on using semiconductor optical waveguides for controlling light. It provides a concise description of the physics and engineering of semiconductor optical waveguides for photonic and electronic switching with a focus on optical communication applications. It provides Python notebooks that illustrate the concepts discussed in the book. The book includes the following topics: linear and nonlinear optics, linear electro-optic effect electroabsorption and electrorefraction, nonlinear refraction, nonlinear optical devices.
There is supporting material in the form of a youtube video
There are are Python and Mathematica notebooks that can be used to help with the design of some of the devices discussed in the book.
Python notebooks at :-https://doi.org/10.5281/zenodo.4506293
Mathematica notebooks:-https://doi.org/10.5281/zenodo.4448672
Enjoy!
thick Al0.25Ga0.75As. The active layer is thick Al0.18Ga0.82As. The cladding layer is thick Al0.25Ga0.75As. The mesa strip is wide and in height. The approximate position of the guided light at the facet is indicated by the red area.
Dewi Nusantara is a liveaboard SCUBA diving boat operating in Indonesia. We were on this boat in September 2019 on a Raj Ampat trip out of Sorong in West Papua, Indonesia. Top of the range dive boat and trip – exceptionally healthy reefs.
Here are some highlights
Pygmy sea horse on fan coral
Manta ray just passing by:-
Feeding fish – I stirred up some sand for the benefit of the bottom feeders:-
The symbiotic relationship between a Goby and a Pistol Shrimp -very happy couple:-
A big bump head fish feeding on coral.
This is a picture taken underwater looking up at the sky and it shows the Snell’s window effect. The Snell’s window is the bright central region of the photograph- it is quite a well-known phenomenon and the dark region at the edge of the photograph is sometimes called Snell’s blanket and that’s when the angle of incidence of the light on the surface of the water is such that no light penetrates the water. It is related to the critical angle for total internal reflection. An easier way to understand this problem is to envisage a point source of light at a depth z in the water -so this inverts the problem but that is ok because the laws of optics are reversible.
The inverted problem about how light escapes from a high refractive index material to a low refractive index material is related to the extraction efficiency of light emitting diodes (LEDs) – in the LED the light is generated inside a semiconductor typically with a refractive index, n1~3.5, and has to escape from the semiconductor into the air with n2=1.0003. Extraction efficiencies can be low because of the large refractive index of semiconductors.
The amount of reflection and transmission at a surface is governed by Fresnel equations. The input parameters into Fresnel equations are the angle of incidence, the refractive index of media and the polarisation of the light. The other consideration is Snell law that gives the relationship between the angle of incidence and the angle of transmission (or refraction) and from Snell’s law, the critical angle for total internal reflection can be determined.
The photograph was taken with a surface between the water and the air which was not perfectly smooth there are ripples on the surface of the water. But to apply Fresnel’s equation to get an insight into the physics behind Snell’s window we are going to assume a perfectly smooth surface. Further in the photograph, we are looking up at the sun and the rays of light are coming in from a particular direction – in our modelling we are going to assume that the light is coming with equal probability from all directions in the celestial hemisphere. The kind of condition approximately by a very cloudy sky what I am going to call a Lambertian sky.
So Fresnel equations, give the fraction of light reflected at a surface between to media with refractive index 
So to explain the Snell’s window in the photo we need to take account of the fact that the angle incidence at the surface (the x-y plane) for a viewer from a depth of z is given by :-
To help visualise the Snell’s window we can use the density plot function in Mathematica and we code the above equations to get the following :-
This for unpolarised light (an average of s and p polarized light) looking up from a depth of 5 meters (the x and y scales are in metres) the refractive index of the water is n1=1.33 and air n2 =1.00 – we assume a perfectly flat surface and light coming from all -directions with a Lambertian sky. It sort of captures the essence of the Snell’s window effect – although it might be more appropriate to call this the Fresnel’s window. Brewster’s angle is the angle at which p polarised light is transmitted with zero loss – there is no equivalent for s -polarised light and it means that under the sea the light is partially polarised.
If you would like to play around with different refractive indices and depths then check out the Snell’s Window simulation So the different refractive indices are appropriate to figuring out the extraction efficiency from LEDs and indeed the injection efficiency into solar cells.
Below is a movie of how Snell’s window at the surface changes as depth increases – it assumes n1=1.33 the refractive index of water:-
The movie below shows how Snell’s window at the surface changes as the refractive index n1 increases – so that it shows how less light escapes from the material as the refractive index increases – it relates to how light escapes from an LED – the depth is 4 microns and the x-y scale is in microns.
Should you ever find yourself having to calculate the refractive index of the semiconductor alloy Aluminium Gallium Arsenide, AlxGa1-xAs – so that’s the alloy with an Aluminium fraction of x. Then click here to see the refractive index as a function of wavelength.
VCSELs (see Brtiney Spear’s take on VCSELs http://britneyspears.ac/physics/vcsels/vcsels.htm )are components in the 3D face recognition system used in the later versions of the iPhone – the VCSELs generate the structured light required to obtain the 3D information from a scene see https://appleinsider.com/articles/18/03/08/apple-vcsel-supplier-suggests-truedepth-coming-to-multiple-iphones-this-fall. They are also used in miniature atomic clocks https://www.photonics.com/Articles/VCSEL-driven_Atomic_Clock_Available_to_Consumers/a46948
The VCSELs include an electrically insulating oxide layer that is used to channel the current in the device. Fabricating the oxide layer is an important part of the VCSEL manufacturing processes and by using a nanoanalysis technique called FIB-ToF-SIMS the atomic species in the device can be 3D mapped with a resolution down to a few nanometers. At the John De Laeter centre of Curtin University, we used FIB-ToF-SIMS to analysis the atomic species in a VCSEL manufactured by Compound Semiconductor Technologies. With FIB-ToF-SIMS we can precisely map out the oxide layer in the VCSEL and determine if it is up to specifications.
When we map out the atomic species of interest in even a small volume we end up with a lot of data – in the movie shown below we show the Gallium, Aluminium and Oxygen atoms in cube volume device 2x2x2 microns – of particular interest is the lower Oxygen atoms -shown in red in the Aluminium oxide layer – the oxide layer on top is a SiO2 protection layer – not really that important for device operation.
Enjoy the movie:-
Bremner bay , Western Australia -there be dragons!
In March 2019 went diving with Craig Lebens of https://bremerbaydive.com and made a video of a Weedy Sea Dragon feeding.
There was also leafy sea dragons but see how well camouflaged:-
but here is a leafy dragon out in the open:-
We were diving at Rottnest http://www.rottnestisland.com, on 3rd April 2016 with the Perth Diving Academy’s https://www.perthdiving.com.au dive boat Lionfish and saw a cute octopus which I think was a frilled pygmy octopus (FPO). Check it out :-
If it was a FPO then it’s the first time it’s been seen on the West coast of Australia according to the Atlas of living Australia :- http://bie.ala.org.au/species/Octopus+superciliosus
But the trouble with identifying octopuses ( or is octopi? http://grammarist.com/usage/octopi-octopuses/) is that because of their ability to change colour to suit their background it’s very difficult to compare photos from different locations.
We were on the SCUBA diving liveaboard Thailand Aggressor for a seven day trip Saturday 10/10/15 until Friday 16/10/15. We did the South Andaman Sea itinerary the details are at:- http://www.aggressor.com/captainlogsview.php?log=4521
On board was an excellent photographer, Gary, he partnered us on many of the dives and he has a web site with the photographs from trip at:-
http://www.naturalexpressions.com/cgi-bin/photo/search.pl?Type=Andaman
Generally, this was a good trip and the crew and dive staff were exceptional in ensuring a fun diving experience. However, there was a lack of big stuff we just saw 1 shark and 1 turtle. There was plenty of evidence of commercial fishing – every night the horizon was crowded with fish boats with very strong lights to attract squid and prawns. Also, from the lack of even small reef sharks, I suspect there was a lot of shark fishing for shark fin soup. The reefs, although still interesting to dive, are showing signs of overfishing.
Below is
On the first day we saw a school of barracuda:-
Also from the first day diving here’s a couple of photographs in our spot-the-fish series first spot the flounder :-
and then spot the stone fish – a bit more important to spot than the flounder because of the highly venomous spines:-
on the topic of venomous spine here’s a lion fish:-
back to more friendly fish and a group of easy to spot finding Nemo clown fish:-
Day2: ever seen a cucumber have a crap:-
And here’s a video of a stone fish blinking – the fish is difficult to see until it blinks:-
Day3: this parrot fish is getting cleaned by small blue wrasse fish – seems to be enjoying it and certainly it was reluctant to move which made it easy to film:-
Below’s a video of a shoal of yellow snappers and if you look at it closely you will see some Blue cleaner wrasse touting for business but none of the yellow snappers stop to get cleaned – I guess some days the cleaners just strike out.
This is a big dog faced puffer fish – check it out:-
Here’s a video of a cuttle fish mating behaviour, according to Clive the dive master “they are always at it” – the video shows a large male protecting the female in contention from challengers – they are flashing to each other signalling no doubt the cuttle fish equivalent of “are you looking at my girl friend”. They are four “Fs” of animal behaviour, fleeing, feeding, fighting and reproduction and is this video we have fighting and reproduction.
I always like the way sea snakes move – looks silky smooth and sinuously sensual – this video shows a banded sea krait checking out the nooks and crannies on the reef looking for prey. The sea krait has a very poisonous bite but, fortunately, it means of delivery, its fangs, are small and designed only for killing small fish – but don’t let a sea krait chew on you because if it does manage to deliver its poison it could ruin your whole day or at least the 3 minutes of it you have left.
charlieironside 