OpenSPAD

OpenSPAD (Single Photon Avalanche Diode - fotodioda lawinowa do pomiaru pojedynczych fotonów) to otwarty detektor światła, działający na zasadzie zliczania fotonów przez fotodiodę lawinową pracującą w tzw. układzie Geigera z układem aktywnego gaszenia lawiny.

Projekt stworzony został przez elektroników z GaudiLabs [1], jako prosty w wykonaniu detektor zdolny do detekcji pojedynczych fotonów. Zastosowania takich detektorów są ogromne, głównie stosuje się je w nauce - w spektrometrii, mikroskopii, fizyce kwantowej etc. Dzięki temu, że układ ten jest w stanie wykryć pojedynczy foton i dokładnie zlokalizować go w czasie, diody tego typu stosować można także w eksperymentach czasoworozdzielczych, takich jak na przykład TCSPC (Time Correlated Single Photon Counting - czasowo skorelowane zliczanie fotonów) do mierzenia czasów zaniku barwników itp. lub HBT (Hanbury-Brown-Twiss, od nazwisk twórców metody) do korelacji emisji fotonów np. w celu wykrywania źródeł pojedynczych fotonów. O tych metodach bliżej może kiedy indziej. Teraz - kluczowy element - sam detektor fotonów.

Impedance spectrometer

Some time ago I was showing 3D render of my impedance spectrometer project. It was planned for a competition on Elektroda.pl, but of course I massively misjudged the amount of time needed to finish the project (it is still not finished). So I cab shed some light on the device, I guess...

Impedance spectrometer is a device that measures the complex impedance - real resistance + imaginary reactance as a function of frequency. It is widely used in sensor applications, biosensing, electrochemistry and material sciences. We will talk about some of the applications later on, when the device will be finished and ready to perform some test measurements.

Setup for optoelectronic characterization of nanostructures

So I managed finally to put together the setup for optoelectronic characterization of nanostructures, consisting of a wide-field fluorescent microscope that we have at work in the institute and my set of devices, namely the precise ammeter and electrode holders together with two power supplies (one for powering the ammeter, second one for polarizing the sample. Sorry for the low quality of photos, but I have only ma cellphone camera here at the moment.

Electrode holders are placed on a metallic plate (in order to fix them to the microscope using small neodymium magnets). The electrodes are made of sewing needles (cheap, easy to get and with a  sharp tip).

Here is the operator view of the whole setup. On the right there is also an PC that is collecting the data from the CCD camera in the microscope and from the picoammeter, using an National Instruments USB DAQ. On the right, next to the microscope, is the PSU used for polarizing the sample. It is capable of outputting up to 200 W or 40 V, whatever is lower at the current moment.

And here is the side view of the setup with the bug PSU powering the ammeter on the right, the ammeter and USB DAQ behind it. The computer controlling the whole thing is not shown here.

So stay tuned for some preliminary results (as soon as I obtain anything that is worth showing).

Electrode holder for a microscope

Today I finished making the blueprints of an electrode holder for an wide-field fluorescence microscope that we have at work. Nest week I'll take this to the workshop and I hope that they will quickly make the whole thing, so I can present it to you ;). And do some cool science of course.

I hope you like it. The electrode holder/manipulator consists of a base plate and top plate connected with springs and a micrometer head for controlling the height of the electrode that will be attached to the insulating teflon holder.

Box for ammeter

Only a samll update today - a full metal enclosure for the ammeter I'm making at the moment. A nice render for the end of the day:

This will be milled from aluminum. You can see three holes for output, power and sample polarization voltage. There is also a hole for input connector on the other side. For input, output and sample polarization I plan to use BNC connectors, and for the power connector a dedicated three pin military-style connector. I hope to have this machined soon, so I can finish mounting the whole thing.

Also a dedicated sample holder will be milled from non conductive Teflon:

On this image you can see an additional set of clamps with golden needles attached. The needles are used to make an electrical contact with the sample.

Vacuum chamber for optical spectroscopy part 3

Okay, so I've got all the parts for the vacuum chamber and assembled the whole thing.

I've started by assembling the window. It is a 3mm quartz plate, sealed with two rubber o-rings (that will be later replaced with fluoride rubber ones)

After that I've screwed down the windows part to the chamber body, sealing this joint with another o-ring. To the vacuum flange an vacuum valve was fitted (Leybold full metal manual valve).

So assembly is done, now for testing it we attached the chamber to pumping station consisting of a rough vacuum pump and turbomolecular drag pump. Pumping station is attached via an metal flexible hose. The pump was left for ~1h to evacuate the chamber.

After one hour of pumping we achieved pressure equal to 1,6 *10e-5 mbar. It is quite good result for that pump. On a normal cryostat pumped for an hour we achieve 5,4*10e-5 mbar, so the results are comparable (the cryostat is slightly bigger). The only one thing to test is the vacuum tight sealing. I'll take a look at the chamber after some time to see if it's still under vacuum.

Some new stuff just arrived

So, I've got some fresh stuff from the workshop. Still in as-received state, but this is a big step for now. Just see how blue-prints turn into reality:

PCB for the ammeter arrived! Not yet populated, as I'm still waiting for the ICs (should be here next week). I hope that everything will fit, as some drills are smaller than expected

Sample holder is also ready. It turned out very nice. Maybe not exactly as in the render, but the crucial parts are ok. Also it is blackened, to limit light scattering from it.

Also the vacuum chamber parts are done, but I still have to put it together - expect some pictures soon.

Sample holder

Some viewers say that I'm getting lazy. To prove them wrong, recently I've drawn a sample holder, that I need to fix my samples in my measurement setup. When everything will be finished I post some pictures of the whole thing, but now - only a drawing from Autodesk Inventor :).

This thing will be used to fix an microscope slide (3" x 1") in a 3 axis stage from Thorlabs. The stage is motorized using linear motorized actuators, also from Thorlabs. This will allow me to automatize a big part of my measurements. Stay tuned.

Reduction ring

I love showing nicely rendered pictures of my projects :3 so here is a small, yet very important thing - an ring with threads, for thread reduction. Outer ring is SM1, and inner is M18. It will allow me to mount a prism in my spectroscope, and this means that I will hove to show it to you as soon as I finish constructing it.

Making these one made me learn how to configure a new thread in Autodesk Inventor, because the SM1 thread is not defined in the software. I anyone would be interested I could make a simple tutorial for that.

Spectrometer will consist of a prism, mounted via this adapter, an an iDus CCD camera. This device is a 1024x256 px camera, designed for use as an spectrometer. I will post some specs later on, when I will show the whole device.

Vacuum chamber for optical spectroscopy part 2

I've got some input from my friends and, what's more important, bosses approval of this project. Here it is how the chamber project looks like now (nice render isn't it?)

Now I'm making technical drawings from this to have it turned and milled at the workshop. This will be made from aluminum (unfortunately, as this is vacuum equipment and should be made from stainless steel), with quartz window and fluor-rubber o-rings for sealing.

Vacuum chamber for optical spectroscopy

I started designing an vacuum chamber for our spectroscopy setup at work to measure fluorescence at low pressure. I would like to share with you some early plans of it. This is an image that I made using Autodesk Inventor to show how it may look finished.

The body will be made of aluminum, the windows (far on the left) probably quarz. The NW25 flange on top is for connecting a vacuum valve and pump.

I hope my boss will like it :).