Author Archives: loiro

Paul Soleillet, again!

If Paul Soleillet has a special section in this website this is probably because I have spent more time reading an understanding his PhD thesis than any other scientific paper. And I have to confess that at the beginning (my first contact with his work was 2011) I understood very little of it. However, this last two years I have been  rereading this work several times, understanding more and more of it.  And every time I was more amazed.

Last year I published how Soleillet pioneered the differential polarization calculus in the third part of his thesis. This year, together with my colleague Shane Nichols, I have published a new paper that emphasizes the contributions of Soleillet to the description of coherence and polarization in 3D (first and second part of his thesis).

Oriol Arteaga and Shane Nichols, “Soleillet’s formalism of coherence and partial polarization in 2D and 3D: application to fluorescence polarimetry,” J. Opt. Soc. Am. A35, 1254-1260 (2018)

I think that some of the results that we emphasize in this paper, originally discovered by Soleillet but that we put in a more recognizable, format  are very important for the  fluorescence polarimetry. If you are interested in the topic, I think our paper will be very useful.

Note about Soleillet’s biographical information

I am still looking for a photo of Paul Soleillet. I cannot believe that a person who died in 1992 and worked in major French scientific institutions for many decades has NO photo! I contact every place where he worked, without any luck.

However a couple of weeks ago I visited the  Archives Nationales in Paris and I was able to access to several original documents of Paul Soleillet from when he  enrolled the École normale supérieure. See below some of them.



The Fresnel triprism, an almost forgotten wonder?

Recently I have become interested in the Fresnel triprism (sometimes also simply known as Fresnel prism). It is a prism made of quartz cemented in between two other half prisms also made of quartz, but with  opposite handedness than the central prism. See below a drawing of this prism from the book “Concepts of Classical Optics, by J. Strong (1958)”  which was republished by Dover in 2012.

Fresnel demonstrated as early as in 1822 that an incident beam of unpolarized light could be separated into its circularly polarized components (by multiple refraction through a composite prism of alternating left- and right-handed quartz segments). Fresnel was describing a phenoma of double refraction in Quartz along the optic axis, based on the the difference in phase velocities of states of opposite circular polarization. The interesting point is that this double refraction is an interface effect at the prism’s interfaces, because left- and right- circular polarization present differential refraction and they are refracted (i. e. deviated) by a different angle.

The triprism produces rays of perfect LCP and RCP, with an angular separation dependent upon the dimensions of the prisms and the wavelength, from a collimated incident beam of unpolarized or plane-polarized light. It seems that the there was a time when the Fresnel prism (or variations of it adding even more prisms with alternating handedness to magnify the effect) was quite popular, and the properties of this Fresnel prism are mentioned in many books. However, nowadays is mostly a forgotten optics relic and, apparently nobody is manufacturing them any more. They can probably still be found in some old laboratories, but I have never had the chance to see one (yes, I am searching one!).

I think that the Fresnel triprism could really helpful to teach concepts about the polarization of light and optical activity, because it is the most clear experimental demonstration that unpolarized or linear-polarized light can be decomposed in LCP and RCP contributions. And more importantly, I also think that the Fresnel triprism could have today many applications in chiroptics, as it is probably, one of the most elegant (and argueably better) ways to generate good circularly polarized light. Remember that current methods to generate circular polarization are almost always based in the use of quarter-wave retarders, optical components that tend to be chromatic and with a non-ideal polarization response. In contrast, crystal-based polarizers tend to be very achromatic and with an almost ideal polarization response because, like the Fresnel triprism, are based in the beam splitting due to double refraction. 

The only paper known to me where the Fresnel prism was used for a chiroptical application is R. Manuel Echarri, The fresnel prism as polarization interferometer, Microwave and Optical Technology Letters 6(7):403-407,1993. See below a figure from this paper. The author of this paper recently told me that the prism he used was lost among old materials and probably was more than 100 years old.

Somebody wants to make Fresnel triprisms again?

Blog recommendation: Skulls in the Stars

Every year I am getting more interested in the history of optics, particularly during the XIXth century and first half of XXth century. The blog Skulls in the Stars  by Gregory J. Gbur contains really interesting posts about the history of optics during this period, with very rich and enriching explanations  than are not found in optics books.

For François Arago fans like myself I cannot avoid recommending the following three posts:

Announcing the 8th International Conference on Spectroscopic Ellipsometry

I am part of the Organization Comittee of the Eight international conference on Spectroscopic Ellipsometry (ICSE8). It will be held in Barcelona in May 26th – 31st, 2019.

You can save those dates in 2019. The abstract submission will start later this year.

Click on the image to access the Website of the ICSE8 Conference

Clicking HERE you can also get the first circular in PDF.

Thoughts about the situation of research in Catalonia and Spain

During the last months international news have reported vastly about the pro-independence movement in Catalonia, which crashed against  the fierce negative of the Spain government to hold an official referendum about the subject, as it was done in Scotland not long ago. These months the controversy has escalated to a new level and, sadly, now part of Catalan Government is in prison and another part is in Brussels and they would be arrested if they entered Spain. I will not write more about this, as I want to focus on about how research is handled in Spain and Catalonia, but maybe this is demonstrating how a country that cannot handle politics cannot handle either research.

The following graphs show the evolution of investment in research in Spain in the period 2009-2016 and compared to other EU countries.

Source: elpais

Continue reading

Young’s double slit experiment analyzed with Mueller matrix polarimetry

Young’s double slit experiment is one of the most famous experiments in Physics. It played a major role in the discussion of the wave-particle duality of light and it is also usually used to explain several basic concepts of Quantum Mechanics.

When the experiment is made with polarized light, the well-known result is that the interference pattern fades out if the slits are labeled with orthogonal polarization states. Beyond this simple statement we have developed some tools that allow for a complete understanding of Young’s double slit experiment from the perspective of Polarimetry. I have summarized this topic in a presentation I recently made in the AVS 64th international conference.  You can visualize or download it here.

Download (PDF, 4.28MB)

This presetantion is (at least partly) related to our recent papers:

The history of the differential Mueller-Jones formalism

Sorry I have not been very active updating this website lately, but research has continued and I have authored several publications since I last updated. You can see them in my Google Scholar profile and others are now under submission.  Anyway, in this post I want to highlight one of my recent publications which is titled Historical revision of the differential Stokes–Mueller formalism: discussion. This paper that was published last month in J. Opt. Soc. Am. A 34, 410-414 (2017).

This paper (which is classified as a “discussion paper” in JOSA-A) in  makes a historical revision of several early contributions to the differential Stokes–Mueller formalism that have been totally overlooked. Most importantly it demonstrates that this formalism was pioneered by Paul Soleillet in 1929, almost 50 years earlier that it was assumed.

Photos of early pioneers of the optical polarization calculus during the first half of the 20th century. From left to right: Francis Perrin (1901–1992) (AIP Emilio Segrè Visual Archives), Hans Mueller (1900–1965), and R. Clark Jones (1916–2004) .

Despite many attempts, I have been unable to find a photo of Paul Soleillet (1902–1992). So let me make here a public call in case anyone is lucky enough to find a photo of him, do not hesitate to share it with me.

Nature (the Journal) and chirality

I am concerned by the way the leading journal Nature deals with the subject of chirality and its relation with optics. I would say that this journal is becoming notorious for publishing papers containing  confusing (and sometimes wrong) statements about chirality. Unfortunately this is not new.

In 2013/2014 I sent to Nature Photonics a short letter titled “A note on optical activity and extrinsic chirality” questioning the concept of extrinsic chirality and explaining how it could lead to very unfortunate confusions. Very long time after the submission the Editor told me that I was right but he argued that everything I was saying was well-known. I was not very satisfied with this response but at least I hoped my note had served as a heads up for the Journal.

A couple of months ago I saw that Nature had published a paper with the surprising title: Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials by AB Khanikaev et al. . This title is already not very promising because two-dimensionality and circular dichroism are, in principle, incompatible concepts, but unfortunately what comes inside can only be described as a  confusing and confused understanding of circular dichroism. This time I wrote another short letter to Nature titled “Circular dichorism and two-dimensional materials” and I submitted it as Brief Communication arising to the paper by  Khanikaev. The editor this time said that this discussion is clear to the metamaterials community and it does not challenges the conclusions of the paper for this community. Sure?

Again, I hope that this second letter has served as a heads up for Nature, but  at this time I can only advise caution when reading a Nature paper dealing with these topics.

Image result for caution advised

BIOAM Workshop, Palaiseau, France , 14-15 November 2016


I participate in the organization of this BIOAM Workshop that will be held in the Ecole Polytechnique (close to Paris) on 14-15 November 2016.

The main subject of the workshop is Biophotonics and Optical Angular Momentum, but it will also cover many aspects about polarimetric theory, imaging.

This is the complete list of topics:


  • Higher order Poincare sphere, generalized Mueller matrix formalism
  • Interaction of spin and orbital angular momentum of light
  • Topological states and scattering
  • Chirality and Optical Angular Momentum
  • Propagation of vector light beams in complex media


  • Generation and analysis of vector light beams
  • Polarimetric instrumentation
  • Super-resolution imaging
  • Biomedical photonics

There are not many workshops or conferences focused on more fundamental aspects about the polarization of light, so I think it will be a great opportunity to gather people interested in this topic.

The workshop Chair is Tatiana Novikova, from the LPICM

On the Ramon y Cajal failure

Currently, the Ramon y Cajal program is almost the only “official” way to get into a sort of tenured-track position in Spain. The “Ramon y Cajal” 5-year contracts are funded by the Spanish Government and are addressed to professional researchers in possession of a PhD degree who have presented a line of research. Applicants must have obtained their PhD degree in the last 10 years and have carried research abroad for at least two years or have their PhD abroad at least two years before the call.

This year, as I had already done the two previous years, I applied for a “Ramon y Cajal”. I submitted my application for the “Material Science and Technology” panel (my last year’s application was in the Physics panel). I have just known that my application has been denied and, according to the evaluation I have received, I have ranked 55 in the panel. Only the 14 top candidates have been awarded with a  “Ramon y Cajal”. So I was not even close to get it.

The evaluation I have got has made me angry enough to to make me want to share it here. These contracts are scored from 0 to 100 point, 50 points depend on the contributions in the CV (i.e. basically publications), 25 point in the participation of international activities, 5 points in other CV merits. The final 20 points depend on the capacity of the candidate to lead an independent research line (this is a sort of more subjective area).

My worst score comes from my CV contributions. From the 50 points I could get here  I have got only 40 and the following comment:

Since the start of the PhD approximately in 2005 the candidate has achieved a good publication record which amounts to more than 50 publications and a relatively high h-index. The candidate is also a recipient of a M-C IIF. The candidate reports 6 papers as the only author and 31 as first author. There is one very high impact journal among all the publications, but several of the publications have and index below 2. The candidate has been invited to several conferences and seminars.

So is the evaluator basically suggesting that I should be ashamed of having several publications in journals with impact factors lower that 2? Should I hide them from my CV and only show those with IF higher than 3? It is true that I have several publications in OSA journals such as Applied Optics or JOSA A with impact factors around 1.5-1.6. But this are fairly good journals and I am quite proud of those publications. Also the reviewer seems to be omitting that in fact I have more publications in journals with IF greater than 3 than lower.

We have reached a point where it makes no sense that a publication in Nature Photonics as 6th author (to say something) becomes more relevant to the (trained?) eyes of the evaluator than a whole  original research trajectory.

In the “participation in international activities” section I have scored 23/25 with the comment: International experience at NYU ( 2 years). The candidate has participated in several international projects. For other CV merits I have scored 5/5 with the comment: R&D 100 Award for Instrument Development issued by the Editors of the R&D Magazine

From the final 20 points that, in theory, evaluate the capacity of the candidate to lead an independent research line I have scored 15 points  and got the following comment:

The candidate has proven the capacity to set an independent research program demonstrated by, for instance, co-ordinating a few projects. However, the level of impact remains an open question given the impact received by the candidate during the 11 year research period reported. The large number of publications as first author and about 6 papers as the only author may indicate lack of interest in carrying out a synergetic effort towards the goals. Recently (according to the candidate himself) has the candidate began a widespread collaboration with several research groups.

So in a section that is supposed to evaluate your independence and your capacity to lead your own research  I am criticized for having some “only author” publications and many first author publication? This makes no sense. I highlighted this as a positive thing in my application to precisely stress that my publication record was self-earned and not because I had been making marginal contributions to research carried or leaded by other people. Obviously the evaluator did not like my remark.  The last sentence of the report I do not know exactly how to take it. All I put in my application (literal words) is: “Currently I am collaborating with the following international research groups:” and I wrote a list of the groups that I am currently collaborating with. Is the evaluator then suggesting that I have not collaborated with anybody in the past?

Anyway, despite being disappointed, I cannot not say I am too surprised. I already knew that what matters most is the “luck” you have with the evaluator you get.  Apparently each application is reviewed by one single person. As at the end, for a given scientific panel, the number of active scientist in Spain is not so large, there are also widespread rumors of evaluators favoring candidates that directly or indirectly know (the human factor!). The list of Ramon y Cajal awardees is available here.  By checking names in Google Scholar is easy to realize that there are very strong candidates, although many  of them do not seem stronger than me (at least in terms of publications). Many top positions are given to researchers that tend to have several (more than 1) publications in a high impact jounal (such a Nature materials, Nature, Science, etc ) even if they are only listed as 5th author of such publications. Is this the way to establish a research career?