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?

Paul Drude Award

Last week I was in the 7th International Conference on Spectroscopic Ellipsometry celebrated this time in Berlin. This is a very nice series of conferences celebrated every 3 years (in earlier days it was every 4 years). My first participation was in Stockholm 2007 as fresh new PhD student and, later, I also participated in all the following editions: Albany (2010), Kyoto (2013) and in Berlin (2016).

In this conference I was honored to win, together with Christoph Cobet, the  Paul Drude Award. The Paul Drude Award is named in honor of Paul Karl Ludwig Drude (1867 – 1906), who invented and first applied ellipsometry. Reflecting Drude’s work related to the electron-conductivity model, emphasis is also placed on spectroscopically determining and understanding the interaction of light with matter.  The Paul Drude Award is given at each International Conference of Spectroscopic Ellipsometry (ICSE) to a young scientist for exceptional contributions to the development and application of spectroscopic ellipsometry.

Some new publications

Relation between 2D/3D chirality and the appearance of chiroptical effects in real nanostructures, Opt. Express 24, 2242-2252 (2016)getImage

Natural optical activity vs circular Bragg reflection studied by Mueller matrix ellipsometry, Thin Solid FilmsFig-3-Spectroscopic-Mueller-matrix-ellipsometry-in-the-cuticle-of-the-beetle-Macraspis

Reconfigurable chiroptical nanocomposites with chirality transfer from the macro- to the nanoscale, Nature materials.nmat4525-f1

Structure vs. excitonic transitions in self-assembled porphyrin nanotubes and their effect on light absorption and scattering, Nanoscale 7, 20435-20441 (2015)Capture3

Optical activity in reflection

When I was a PhD student I remember  I often wondered  why circular dichroism (CD) was measured only in transmission.  At that time I was already familiar with ellipsometry measurements (in reflection) that are typically used to determine the dielectric function of materials and I did not understand why optical activity, arguably also a optical property of material, seemed to manifest transmission but not in reflection.

It took me some more time to realize that all was a mater of scale. I learned that optical activity can (in some occasions) have some effect on the specular reflection of light onto a surface but, this effect, was too subtle to be “seen”. The literature about this topic was very scarce, and this question was only properly analyzed in several helpful papers published by Mark P. Silverman in the 80s and 90s.

Last year I had the intuition that I would be able to sense optical activity in reflection if I chosed the adequate material and had the right instrument (I had it!). I discovered that this suitable material should have a large optical activity (this is not too surprising!) but also have a very anisotropic gyration (i. e. with its values changing a lot with the orientation). This is why I started measurements on a AgGaS2 crystal. All these steps eventually ended in this recently published paper: O. Arteaga, “Spectroscopic sensing of reflection optical activity in achiral AgGaS2,” Opt. Lett. 40, 4277-4280 (2015).

Fig. 5.

This measurement is more than an anecdotal verification of an idea because it proved to be also practical. It allowed the study of optical activity in spectral regions that cannot be studied in transmission.

A note on optical activity and extrinsic chirality

“Optical activity produces a differential absorption or refraction according to the handedness of circular polarized light, but the inverse is not necessarily true: a differential absorption of refraction of circular polarized light does not imply optical activity”

This simple statement has been sometimes overseen and there exist some confusion among researchers studying optical activity in several fields of science, from chemistry to material science.

Last year I  wrote a short comment addressing this topic and with the focus on metamaterials and nanostructures.  It was under consideration in Nature Photonics for a long time, but finally they decided that  this topic was already clear and had been discussed elsewhere. Just in case I make it now available as a preprint at:

Abstract: It has been assumed that optical activity can be measured by illuminating alternatively a material with left- and right- handed circular polarized light and analyzing the differential response. This simple and intuitive approach is in general incorrect, and has led to misleading idea that extrinsic chirality involves optical activity.

Evolving Mueller matrix microscopy

For over a year and a half I have been working on Mueller matrix microscopy.  Now I can say that I have no doubts that, when it is properly implemented, Mueller matrix microscopy is nothing but the perfect upgrade for polarization microscopy. I know polarization microscopy is not the most trendy technique in these days, but polarization microscopes are so widespread that even if only a tiny fraction of core polarization microscopy users become aware of what Mueller matrix microscopy can offer, the usage and the applications for Mueller matrix microscopy will grow exponentially.


Detail of the scale of a Morpho butterfly captured with a Mueller microscope.

With this objective in mind we have been working in the last few months on a compact, table-top prototype of a Mueller matrix microscope. The skeleton and the optics of the instruments are based on commercial polarization microscope, but it has been heavily modified to work as a fully-automatized Mueller matrix microscope. The aim was to keep all the advantages of polarization microscopy, with a very compact instrument in which it is very easy to manipulate the sample and find a focus but, at the same time, all the power of Mueller matrix analysis is just available after a “click”. The working principle of this Mueller microscope was described in Oriol Arteaga, et al. “Mueller matrix microscope with a dual continuous rotating compensator setup and digital demodulation,” Appl. Opt. 53, 2236-2245 (2014).


Photo of our benchtop Mueller matrix miscroscope. It is based on classic ZEISS Jenaval microscope that has been modified.

The project is being carried with the technical collaboration of  A.COLOMA Microscopios y Aparatos Ópticos and we work together to offer complete solutions for Mueller matrix microscopy. At this early stage, you can contact me ( or Francesc Gomez (  in case you are interested on getting a Mueller matrix microscope or if you would like to make a custom modification on your  polarization microscope.

 UPDATE! Click on the following image the pdf version of a presetation about MM microscopy that I did some time ago.