Thursday, June 30, 2011

Celebrating the 50th Anniversary of Nonlinear Optics

During NLO 2011 there will be a symposium celebrating the 50th anniversary of nonlinear optics.

I don’t want to emphasize the well-known speckle which was removed from the famous paper in Physical Review Letters by P. Franken, et al., demonstrating nonlinear optical effects for the first time appeared in 1961. I do want to pay tribute to the great scientist Raman here.

Let us start with a question: When Raman observed Raman scattering in 1928, there was no laser. What was his light source?

(I wish I had prizes for correct answers!)

The answer----“The apparatus used by Raman for the discovery consisted of a
mirror for deflecting sunlight, a condensing lens, a pair of complementary glass filters,
a flask containing benzene and a pocket spectroscope. the total cost not exceeding $25 ” [1]

Raman observed not only the Stokes radiation, which has the lower photon energy than the incident photon, but the extremely weak anti-Stokes radiation.

Below are a few notable things that I know about the symposium invited speaker:

Plenary session speaker Steve Harris discovered optical parametric fluorescence (Wonder why it is called parametric oscillator? ). What less known is that he is inventor the acousto-optic tunable filter. He filed the patent “Tunable acousto-optic method and apparatus” in 1970. Now one type of pulse shaper--Dazzler made by FastLite in France--is based upon this. Whenever we disucussed the acousto-optic tunable filter, my thesis advisor, who was Professor Harris’s graduate student, always made sure the audience know about this history and gave Professor Harris the credit.

Professor Bloembergen, who was awarded a Nobel Prize for his contributions to the field of nonlinear optics and to the development of laser spectroscopy in 1981, will give a talk on the birth of nonlinear optics. I look forward to that talk.

Robert Byer probably will speak about the history of the nonlinear optics. I had a glimpse of his talk from his website, which shows a lot of pictures and fascinating stories. For example, he has a funny picture about “Who Invented This Crazy Idea (of laser driven fusion), Anyway? ” By the end of the 85-page-pdf-talk file there is a picture of Surfing Ocean Waves at Poipu Beach, Kauai. The video is great. I know it will be event better to hear the talk in person!

Algis Piskarskas, the Head of Department of Quantum Electronics and Laser Research Centre at Vilnius University, serves as the one of the advisory board member of the Virtual Institute for Nonlinear Optics (VINO, where they promote open sharing of know how, infrastructures and resources. They have a logo which is a beautiful picture of conical waves:

GĂ©rard Mourou, the inventor of the chirped pulse amplification and the famous book Quantum electronics author Amnon Yariv are also among the invited speakers.

Inspired by another principle of VINO: wider concept and visualization based on the search for truth and beauty in the world that surrounds us, I would like to show a picture that I took during my experiment but have not published.

Above, three sets of sidebands generated in a 160 micro meter fused silica with a pair of fs IR pump lasers.

Without lasers, or without nonlinear optics, we will never see this beauty.

If time allows I will write a follow up blog after I hear talks from the invited speakers.

If you have any comments, please email me at

[1] R. S. Krishnan and R. K. Shankar, Journal of Raman Spectroscopy 10(1), 1

Friday, June 24, 2011

Frequency Combs and Waveform Synthesis---Toward synthesis of arbitrary optical waveforms

(Please click on the images for a high-resolution one.)

You may be familiar with the function generator, which is available in most of the physics labs and the simplest version of an electronic waveform generator [1]. It is much more difficult to synthesize arbitrary optical waveforms since the optical frequencies are much higher. The electronic synthesis is generally limited to ns time scales while the optical synthesizer is in the femtosecond range.

Synthesizing optical waveforms requires both broadband coherent light and precise control over the phase and amplitudes for the frequency components. Therefore it is natural to combine the frequency comb technology with the pulse shaping technique, which may enable optical arbitrary waveform generation (OAWG), as discussed in a progress article written by Steven Cundiff, the session presider and A. Weiner, one of the invited speakers in the same session and the most famous person in the pulse shaping area [2]. The application, as pointed out by the authors, “are still a matter of speculation,” as "OAWG is still in its infancy." It can be used for coherent control, generation of attosecond pulses etc.

Currently most of the research is focused on only a small number of comb lines. The results, however, are very exciting. For example, Kung’s group recently demonstrated synthesis and measurement of ultrafast waveforms such as square and saw-tooth fields by using 5 frequency harmonics [3]. The result is similar to the following figures. Due to copyright issues I can’t put the original figures here. Kung is giving a talk in this session as well.

Our group also just achieved pulse-shaper-assisted phase control of 5 Raman frequency combs, which is what I am going to present in the conference. The difference of our work from Kung’s is that our comb itself has broad spectrum. So we not only need to correct "local" phase distortions on each spectrum, but also need to "globally" adjust the relative phases of the sidebands. We manage to make the sidebands "dance" in unison, as shown below.

The SHG spectrum of the 5 sidebands after the BBO crystal as we vary the AS 3 phase from 0 to 9 pi, after we adjust the relative phase among all sidebands to be equal.
A: SHG of AS 1; B: SFG of AS 1&2 ;C: SHG of AS 2;D: SFG of AS 1&4, and AS 2&3; E: SHG of AS 3, SFG of AS 1&5, and AS 2&5; F: SFG o AS 3&4;G: SHG of AS 4.

Session presider Steve Cundiff is the 2011 NLO program chair. Many people probably know him through his work and the book “Femtosecond optical frequency comb technology” book, which is edited by him and Jun Ye, who will give an invited talk at this session.

I am not so familiar with C. Fabre’s work. As I Google him I only found his website in French. When I use the Google translation, I get the following----which is almost as funny as if you put an ancient Chinese poem and use the Google translation to get the English version. I love the last sentence---“to measure travel time fine”.

At last, I would like to mention somewhat related work---Multiple independent comb shaping (MICS) by Marcos Dantus. The comb is not “frequency combs” but more strictly speaking “pulse shaper pixels." as explained to me by Dmitry Pestov, who works with Marcos Dantus. The similarity lies in that it does phase shaping of a pulse to generate complex waveforms [4].

[1] Toward Synthesis of Arbitrary Optical Waveforms, Deniz D. Yavuz, Science March 2011, Vol. 331.
[2] Optical arbitrary waveform generation, Steven T. Cundiff & Andrew M. Weiner,Nature Photonics, Volume: 4,Pages:760–766, Dec. 2010.
[3] Synthesis and Measurement of Ultrafast Waveforms from Five Discrete Optical Harmonics, H. Chan, Z. Hsieh, W. Liang, A. H. Kung, C. Lee, C. Lai, R. Pan, and L. Peng,Science, vol. 331, 1165-1168 (2011).
[4] Generation of Complex Optical Pulse Sequences by Multiple Comb Shaping, Dmitry Pestov, Vadim V. Lozovoy and Marcos Dantus, OPN, Dec. 2009.

Friday, June 17, 2011

Women in optics

Most of you who read this blog probably have received an email newsletter from OSA yesterday. I was offended when I read the first sentence of the message from the president (President’s message, JUNE OPN): “If you’re reading this, the chances are you’re male.” I am a female yet I am reading this, I said to myself. As I read on I realize that the president tried to help women in optics. He mentioned that “our best estimate is that fewer than 1 in 10 of our regular and Fellow members are female.”

There will around 150 participants for the 2011 NLO. I wonder how many of them are female? 20 years ago I started college in the department of optical engineering department in Zhejiang University, which is the first institute for optics education and research in China. The ratio of female and male students is 1 to 7. After we graduated, I am the only one of the 8 who shared the same dormitory who continues to be in optics.

As one of the very few in the Quantum optics group here lead by Dr. Scully, I realized that I need to do something to stand out the female dominated workplace. Most of the times, I am the only woman in a meeting. I started to wear pink shirts, in an effort to light up the dark color dressed men during a meeting or conference. I wear pink so often that one of the professor once called me “pink lady”.

A picture of me standing in front of my poster in last year Ultrafast Phenomenon conference

I do feel what the OSA president Chris Dainty said in the message “Women in optics…somehow feeling that they are neither a 'proper woman' nor a 'proper scientists.'” The reason, however, is different from he stated that women in optics being isolated or treat differently. My supervisor has three female Ph. D. students (out of a handful women who received Ph. Ds in the whole department) graduate in his lab the last few years. He is very supportive of my work and has offered me flexibility of working part time in the lab. I have been here in almost 10 years (due to family reasons I stayed here as a postdoc after I get my PhD.) so now being a senior member in the lab I am pretty well respected by my colleagues. Yet, the feeling of not a “proper woman ” is due to the constant feeling of I don’t spend enough time with my kids, while the feeling of not a proper scientist arises from I can’t work many long hours as an experimentalist because I want to be at home at kids’ bedtime.

When I was 4 month pregnant with my 2nd baby I met Paul Corkum (Canadian physicist specializing in attosescond physics and laser science) at a conference in Canada. I mentioned to him my concern of being a mom of two and working full time. He said he actually liked his female PhD students. The reason: although they can’t be physically in the lab many hours but they think more while they are away from work. Many times when I am frustrated with not having enough time to work, I always remember his encouraging words.

The president mentioned mentorship in his newsletter. In 2006, USC started the first Conference for Undergraduate Women in PHYSICS. Now there are northeast conference (Yale-MIT), California Conference , Midwest Conference and Southeast Conference. Next year, for the first time, Texas A&M University is possibly going to host the southwest conference. I, as one of the organizing committee member, try to help other women in physics. There are many great talks by successful women in this conference. Hopefully this will also promote more women undergraduates study optics as well.

At the end of the message, the president referred to excellent resources on this subject. For those of you who are interested please have a look.

Wednesday, June 15, 2011

presentation and communication skills

Recently OPN Career Focus column published two articles by Jean-luc Doumont on the subject of "Creating Effective Presentation Slides" (click here for a podcast and "Communication Skills for Researchers ." both of which give great advice on the art of science writing.

Sunday, June 12, 2011

Military Globalisation

Tarak Berkawi’s excellent short piece for Aljazeera reminds us that Military Globalisation is Nothing New. It outlines the historical principle that colonial and imperialist ambition projects military might abroad, circulating soldiers from place to place or training indigenous militias to suppress popular uprisings. The piece also shows the seldom connected back story to those positive narratives of global free trade and economic liberalism, a world in which the military act as the ‘steel frame of globalisation’. Much of this may seem obvious, but it is refreshing to read something that doesn’t root military activity simply to territory or ‘national defence’ but exposes the trans-national complexity of current military activity.

Friday, June 10, 2011

Good books---The craft of scientific writing/ presentation by Michael Alley

I am currently writing a paper. When I compared the current version with the abstract I submitted to the conference, I saw a huge difference. I recieved a comment on a review paper--at the end, the reviewer said:

“it may help with a little more polish on the English, especially on the use of articles (a, the, etc.) in a few places.” I am not a native English speaker.

When I visited Dr. Rick Trebino’s lab, he mentioned the book “The Craft of Scientific Writing”.

I tried to get it from our library but it turned out it was a very popular book. It was on course reserve. (Like all the good books!)

Then I found and read another of his books, “The Craft of Scientific Presentations: Critical Steps to Succeed and Critical Errors to Avoid.” This book was instrumental in helping me give a persuasive job interview talk.

During spring semester I tried to borrow “The Craft of Scientific Writing” but it is still on course reserve. I don’t want to buy it because I have several shelves of books at home already. Someday, the book shelf may fall down.

Once I asked a librarian when the book will be free to public. He said it is possible it will be always on reserve.

“Then can you order another copy?” I asked.
“No, you know the economy.”

But, he said, you can use the “get it for me” service. It works like this, you submit a request, they will get one for your from another library. I did it. Soon I got the book from Texas Tech. (Thank you, Texas A&M librarians!)

There are many good tips, but I would like to focus on the language aspects:

There are six language goals:
Precise: you must say what you mean
Clear: avoid things you don’t mean
Forthright: convey a sincere and straightforward attitude
Familiar: Anchor your language in the familiar
Concise: every word should count
Fluid: smooth writing, writing with transition, writing that moves from sentence to sentence, paragraph to paragraph without tripping or tiring the reader.

All these are quite useful for revising my paper.

But maybe using “a the that which” is indeed a difficult subject so the author avoided it. I didn’t find any description to this confusion. The book refer to Richard Feyennan’s writing very often (He actually used Richard Feynman on his book cover to "The Craft of Scientific Presentation).
From the reference I found Richard Feynman’s article published in Physics today Feb. 1988 (he died at the same month)--- “An Outsider's Inside View of the Challenger Inquiry”, in which he wrote: "I finally got it through to the point where it was, at last, in the hands of a real editor, a capable man by the name of Hansen, who changed all my whiches to thats and thats to whiches."

I feel optimistic!

Finally from the, I find this useful article:
"A, An, The" definite and indefinite articles in English .

Thursday, June 9, 2011

Rick Trebino

Since I knew I will be giving a talk at the 2011 NLO I keep checking the website, not so much for the program but to look for updates on the exhibit vendor information. The reason---I hope to see Rick Trebino again.

Last year, after I came back from visiting his lab, I looked back and realized that I actually have interactions with him for many occasions in the past few years, although I didn’t meet him until last year at the 17th international Ultrafast Phenomenon conference.

I heard about Dr. Trebino by somehow getting to know his FROG website. I loved his lecture notes and his book. I like the name he gave to his product--- FROG. Once I even tried to use his lecture notes to give a study talk at Texa A&M Univ. in 2003 or 2004. It didn’t go very well because I just started in ultrafast optics and so many things are beyond my explanation.

Then in 2005, a team of us was working on the Hybrid CARS for the anthrax detection project. We had trouble looking for four wave mixing manually using a translation stage. I was brave enough and directly emailed him asking for advice. Surprisingly, he replied to my email and also asked his student to write to me more. That’s the first time I experienced his kindness and generosity.

After that, I repeatedly returned to his website and studied his book. I read many of his papers. Then in 2010 I unexpectedly met him and his wife during the 17th UP conference. We talked. I wrote a blog about him last year.

Linda, his wife, suggested me come to visit his lab and discuss the question of measuring “holey spectra” (spectrally separated peaks, Nicolas Forget is the one started to call it this way. I think it is funny) we have. She also helped me tremendously before and during the visit.

My supervisor Alexei approved the visit. In Aug. Ben, a graduate student who is working on the femtosecond filamentation, and I went to Georgia Tech. Linda arranged an office for us. Dr. Trebino’s graduate student Jacob Cohen helped us get all the paperwork and a yellow wasp ID (buzz card) and finally a key to the lab. We lived in a hotel and went to school every day, had discussions and looked around the lab. We also tried to work on one small project—using striped fish to characterize filamentaion.

In between I wrote this email to Alexei:

The lab overall is an ideal lab a person can imagine. Many bins for putting different things. Plenty of overhead shelf space. Tons of different mirrors, mounts, etc. Everything are labelled well and in drawers if not used. Everyone has his/her own project and laser. They have 1 amplifier and several oscillators. many Cameras, spectrometers in the beam to monitor the beam. Fixed, no need to move around. Lab is very clean, many optical tables. Students work on their own schedule. They have a book shelf with many optics books. a lunch room (also the showroom, or conference room, has computer, projectors), which is close to the entrance of the lab, have an office space. Jake said every morning they come and discuss first. They normally on each other’s papers and they help each other with experiments. After graduation, anyone can work in Rick’s company if they want. They have extra office spaces. Me and Ben have 2 offices but we stay together in one so we can discuss. They even prepare a computer for us. Here everything is so open and everyone shares. His wife is not a scientist but she is administrating for Rick’s professorship and company.

Rick's lab

(If you want to read more, please click here Rick’s lab)

By the end Rich had a party for us at the night before we left. We visited his house. From 6pm to 10:30pm Rick talked for a few hours, almost non-stop. I felt his hospitality, his enthusiasm toward life and his energy. Linda also talked in between, a typical of a couple in harmony when one will help each other remember things and describe. When I asked how many countries have you been to. Linda thought for a little bit and said” maybe you should rephrase the questions as: Which country I have not been to”.

Rick's home

Later from his website, I learned he even hosted class party for the students who take his class by the end of the semester. I wish I were one of his students.

By that time we had just learned about his funniest ever essay “How to Publish a Scientific Comment in 123 Easy Steps”. That night, Rick mentioned he is writing an essay book. The essays are available on his file sharing website listed under stories. I especially like the Hawaii one. I hope it get published soon so that more people can know his wonderful life.