‘Yesterday i had the honour of drinking coffee with Madam Joliot-Curie’. Those were the words of my father, who was an engineer in charge of the electricity network of The Three Valleys in Savoy. He went on to say that she was a very important personality who had received the Nobel Prize. I was about five years old and it was the first time that I had heard the Nobel mentioned. The rapid electrification of France after the war made it necessary for my father to travel. I was born in 1944 in Albertville, Savoy, with my two sisters, Jacqueline and Michèle. A few years later we moved to Moûtiers, the gateway to the Tarentaise and The Three Valleys, with its well-known skiing resorts, Courchevel, La Plagne and Val d’Isère, etc … I keep in mind an unforgettable memory of the town of Moûtiers, braced between those majestic mountains. Its cathedral and medieval bridge spanning over the tumultuous Isère were impressive and fascinated me. I learnt how to ski at Moûtiers on the slopes of the Champoulet hill. In springtime there were walks with the schoolmaster or priest on Thursdays in the mountains, so high up for the child that I was. In summertime my parents sent me to a boarding house with an authentic Savoyard family living in a chalet in which the main room was divided by a curtain into two parts separating the cows from the inhabitants. This was pure bliss, and those moments will always remain with me. I was nine years old when my father was transferred to La Voulte-sur-Rhône.
The Rhône valley replaced my beautiful mountains. I had to leave my skis and my sledge behind. It was heartbreaking for me, reminiscent of the child Kane’s Rosebud scene in the magnificent film “Citizen Kane”. La Voulte, with its famous rugby team, was very sports-oriented and I replaced skiing with swimming, which I loved.
My father, being an electrical engineer, knew about electro-magnetism, which is a starting point for many fields in physics. He enjoyed sharing this knowledge with me in the way of small problems. I was fascinated by light and the speed of light, which travelled distances seven times the circumference of the Earth or the distance from the Earth to the Moon in one second. That is how he came to explain that we were nowhere near seeing Martians on Earth, contrary to what sensational newspapers were announcing. He taught me how to play chess, which we often did in the evening.
The summer holidays were either spent in Provence with my grandparents on my mother’s side or in the Aude at Espéraza near Carcassonne. In Provence we spent our holidays with our cousins in the medieval village of St Martin-de-Pallières where the castle dominates the village and its park offered us a marvellous playground. The rhythm of our daily life was set by our grandmother, Mané, who we all loved and respected. It was a simple and modest way of life. We would go and retrieve drinking water from the fountain at the bottom of the village. The village school-teacher was my uncle, a voracious reader with an enormous library. Before the advent of television, he along with the school-teachers from the neighbouring villages had created a cinematographic club which regularly featured what today are the great classics. This period certainly awoke in me my deep interest in classic films. Sometimes we would have a visit of one of my mother’s first cousins who had two daughters: Andrée and Marcelle. Marcelle, with whom I had much in common, was later to become my wife.
In the Aude at my grandparents’ on my father’s side, my grandfather was a fascinating character due to his joviality, his kindness, his talent for story-telling and his dexterity. My grandparents were very endearing, and it was a pleasure to spend my holidays with them. My grandmother was an excellent cook and as to my grandfather, he was a brilliant do-it-yourself man with golden hands. He had a workshop where we spent a lot of time together inventing and innovating. Although he had only received a primary education, he loved history and we spent many hours visiting Cathar castles or talking about how the locks along the marvellous Midi Canal worked. He was also an excellent gardener with two gardens at both ends of Espéraza, Fa and Couiza. As we left the table after one of those Sunday meals prepared by my grandmother, my grandfather would invariably ask which way we would prefer to go? To Fa or to Couiza? This was to amuse me a few years later when reading Proust and Madame Verdurin would also invariably ask her hosts the same question: a walk on the Swann side or on the Guermantes side? I was overwhelmed to stay with our relatives, hearing their typical and irresistible southern accent and expressions. It was a bliss to be soaked with my cousins during few weeks in a medieval town like Carcassonne or in a cathar city like Fanjeaux, where I had my first taste of cassoulet de Castelnaudary and blanquette de Limoux the ancestor of champagne.
My father wanted his son to have a technical education, and a very renowned school near Grenoble at Voiron offered advanced technical studies in preparation for the School of Arts et Métiers. It was the Voiron National Technical Lycée, in the Grenoble region, commonly known as the Nat. We sat a difficult exam in order to gain entry to the school in the fourth year. We studied general subjects: mathematics, French, English or Italian but also a number of technical subjects such as industrial design, mechanics and workshops. I was an average pupil, a dreamer and easily distracted. At that time these defects terrified my parents, especially my mother, but they would become precious assets later on in the course of my career as a researcher.
After a Technical High School Diploma and the baccalaureate, in 1963 I entered the University of Grenoble, where I passed a Master’s degree in physics in 1967. Meanwhile Marcelle, who was an excellent gymnast at a national level, entered the École Normale Supérieure of Physical Education (ENSEP) which was then at Chatenay-Malabry near Paris. In the same year we married and went up to Paris, Marcelle in order to complete her training at the ENSEP, and I to start a postgraduate degree in physics (DEA) in order to do a Ph.D. We were living in Chatenay-Malabry near Sceaux. It was predestined. Our apartment belonged to the same landlord family that rented to Pierre and Marie Curie in Sceaux, south of Paris. The landlord was a charming talkative man who was proud to tell me that he had manuscript letters from Mme Curie. One day as we were in the garden, I asked him if it would be possible to see the letters. He went back to the house to bring me a note written by her, complaining of a leaking faucet that needed to be fixed urgently. The great couple was not working only on lofty problems. They had also their pedestrian moments. As I was in search of a post-graduate subject, I came across Jacques Ducuing, who had just come back from Harvard and who was starting a post-graduate degree in Non Linear Optics. That was in 1967 and it was the first time I had heard this term which, associated with the laser, immediately captivated me. I applied for this post-graduate degree straightaway.
Now I had to find a research laboratory. At the Optics Institute I came across an advertisement looking for a researcher in the laser field. It offered a position in research at the Ecole Polytechnique in Professor Vignal’s laboratory directed by Alain Orszag. My career as a researcher was launched.
My first scientific works at the Ecole Polytechnique
Of course, during the first months I was very impressed to find myself at the very spot where so many great scientists such as Ampère, Fresnel, Fourier and many others had distinguished themselves.
This was only 7 years after Theodore Maiman’s laser demonstration. The work I was assigned was in fact a prelude to the work that led to the Nobel Prize. It consisted in the analysis of the frequency of a Q-Switch laser. The latter was not constant and varied during the pulse time. It presented a frequency drift, which in English is called a ‘chirp’, during the pulse time. The idea of this project was to exploit this ‘chirp’ in order to reduce the duration of the pulse by compression. This experience in the nanosecond regime did not present much interest, the ‘chirp’ being too weak and unable to lead to spectacular results. However, it was very important for my experimental formation and would be demonstrated 10 years later with success and thus permit the production of the first femtosecond pulses corresponding to a number of optical cycles. Combined with amplification it would be the basis for CPA (Chirped Pulse Amplification), for which I was awarded the Nobel Prize in 2018.
After passing my DEA in 1968, in conditions complicated by the May demonstrations, in 1970 I passed my doctoral thesis of the 3ème cycle (equivalent at that time to a Masters thesis) on the drift frequency of Q-switched lasers. During this period we also had our first child, Julien.
The call of North America, my first steps in the picosecond field
In 1970, I began my military service. At that time, it was possible to serve as a scientific cooperant in French-speaking countries. My thesis director Georges Bret, who founded the Quantel company, introduced me to Professor Marguerite-Marie Denariez-Roberge from Laval University. She was one of the first people in North America to have a picosecond laser. For three years I studied the kinetics of dye in the picosecond field. I was passionate about this field. I was still enrolled at the University of Paris and in contact with Professor Guy Mayer, with whom I prepared and passed my doctoral thesis (Doctorat d’État, which is equivalent to a PhD) in October 1973. During this period our second son, Vincent, was born.
After my thesis, I, together with my little family left for a post-doctoral year at the University of California in San Diego. Employed by Professor Michael Malley, an extraordinary man who had a picosecond laser but above all also had one of the first Optical Multichannel Analysers, OMA. The OMA allowed us to do away with photographic plates. It was far more sensitive while permitting the recording of light signals in real time.
Equipped with a detector well-suited to the task, I was the first to discover the manner in which to observe the movement of molecules or to measure the fluorescence time of the latter in the picosecond field. Personally, I consider this to be my first major discovery. I was experiencing epiphanic moments which attracted me to the field of ultrafast physics in a definitive and irreversible way.
Return to France, introduction to ultrafast physics on the Palaiseau plateau
Ever since I had left France, I remained on very friendly terms with Alain Orszag. We agreed that after my post-doctorate year in California, I would return to the Laboratory of Applied Optics, the LOA. We thus returned to France in 1974 and I introduced ultrafast optics to the LOA with the help of André Antonetti and also Gilbert Bourdet. At the same time the École polytechnique (’X’) was moved to the Palaiseau plateau and the LOA relocated to the ENSTA (Ecole Nationale Supérieure de Techniques Avancées) premises. We were living in this nice town of Dourdan in the south-west part of Paris. Our house was at the foot of the beautiful castle built by Philippe August in the XIV century. Julien and Vincent had a wonderful time.
At that period, I read David Auston’s article about the use of the picosecond laser for electronic switching with just a gap on intrinsic silicon. The switching was realised by the creation of carriers, produced by the laser photons in the silicon gap. I marvelled at the simplicity and the elegance of the device which could produce perfectly synchronised high voltage pulses without any laser ‘jitter’. Among the applications, I saw the switching of streak cameras which had a serious ‘jitter’ problem.
The first experiments on switching were realised at the LOA with Antonetti but also Alain Migus who had joined us with financial help from the CEA (Commissariat for Atomic Energy). During this period, we had the pleasure of welcoming Michael Malley on a sabbatical year at the ENSTA. Michael was assembling the first femtosecond ‘dye’ laser with Alain Migus and Jean-Louis Martin, who had joined us, bringing with him information and advice given by Erich Ippen from the Bell Laboratories. Our switching experiments were presented in 1978 to the Conference on Lasers and Electro-Optics (CLEO) in Washington. My results attracted the attention of Wolf Seka from the Laboratory of Laser Energetics (LLE) at Rochester, NY. After an animated discussion, Wolf understood the interest of introducing femtosecond pulses in inertial fusion to diagnose implosion. A few months later, I received a phone call from Wolf telling me that the LLE was offering me a position as a scientist. I had thoroughly enjoyed my sabbatical year in the US and also had the feeling that I would evolve more easily in this field that appealed to me in the US. After talking it over with Marcelle, a few weeks later we decided to accept the offer and in September 1977 we left for Rochester along with our two children. However, both of them were sad to leave beautiful Dourdan.
The LLE had just been built. This laboratory was financed essentially by the Department of Energy (DOE) and dedicated to inertial laser fusion. My first impression was that I had made a big mistake. Laser fusion was not my field. I preferred smaller projects, less programmatic ones. However, a few months later my opinion was to change radically.
The University of Rochester in the 1980s played an important role in the development of the field of ultrafast science and technology. The Institute of Optics and the Laboratory for Laser Energetics (LLE) occupied centre stage. The Institute of Optics provided exceptional students and LLE a unique technical platform. Many of the techniques that the researchers in the field use today, like THz generation, picosecond electron diffraction (PED), electro-optic sampling (EOS), chirped pulse amplification (CPA), and jitter-free synchronization, were conceived and demonstrated by the ultrafast science group. The Institute of Optics students – Wayne Knox, Theodore Sizer, Irl Duling, Janis Valdmanis, James Kafka, Donna Strickland, Maurice Pessot, Jeffrey Squier and John Nees – formed the core. Their enthusiasm was infectious and contributed much to attract students from physics, such as Steve Williamson, Theodore Norris, and Kevin Meyer, and from electrical engineering, Daniel Blumenthal, John Whitaker, and Doug Dykaar, as well as faculty like C. W. Gabel, Robert Knox, Charles Stancampiano, Thomas Hsiang, Roman Sobolewski, Adrian Melissinos, Joseph Eberly, and David Meyerhofer.
In the early 1980s ultrafast science was dealing with eV energy-level phenomena. Our group extended its range into the meV on one side, with the introduction of THz beams and electro-optic sampling (EOS) techniques, and to the MeV-GeV on the other side, with chirped pulse amplification (CPA) and its ability to produce relativistic intensities. Work in this area mainly started at LLE in 1978 after my arrival. LLE was running a highly programmatic effort on inertial confinement fusion. At that time the director and founder, Moshe Lubin, and later Robert McCrory understood the importance of creating and supporting in parallel to the main research activity a group that would work on weakly related laser fusion projects,which could offer the flexibility and the type of environment that PhD research demands. I would be in charge of this group, known as the ultrafast science group.
I was impressed by the work of Dave Auston at AT&T Bell Laboratories, which demonstrated that electrical signals could be switched with picosecond precision. Here I had the opportunity to demonstrate that this simple technique could find some important applications in laser fusion because of the need for synchronised high voltage pulses for active pulse shaping or for jitter-free streak cameras.
An exceptional undergraduate student, Wayne Knox, shared an understanding of the importance of this line of research. At Wayne’s high speed of progress, we extended Auston’s work to very high voltage and applied it to the synchronisation of streak cameras. For the first time the streak camera could be used in accumulation mode. Weak luminescence signals could be accumulated, improving their signal/noise ratio. The jitter-free streak camera found immediate applications in photobiology with the group of Wayne’s father, Professor Robert Knox. This technique is now routinely used in synchrotron-based femtosecond x-ray diffraction experiments. High voltage switching also has applications in active pulse shaping, as demonstrated in collaboration with John Agostinelli (student of C. W. Gabel), and in contrast improvement with Wolf Seka. This technique is still used today in high field science.
A streak camera is a beautiful photon-electron transducer. It makes an electron replica of the photon pulses. The electrons are deflected across the phosphor screen, leaving a phosphorescent track. I was mesmerised by the thought that we could use this perfectly synchronised photoelectron pulse to perform time-resolved electron diffraction in the picosecond time scale by simply locating a sample under study in the camera drift region. We could study solid-liquid transformation simply by using a short optical pulse to produce the phase transition and the electron pulse to probe the structural change that would follow.
I asked a new student with great passion for research, Steve Williamson, if he would be interested in this project. This was an enormous challenge, as none of us had any kind of electron diffraction experience in steady state let alone in the transient regime. But Steve was a superb experimentalist, and in one year he built a complete “streak camera” and demonstrated the concept. We applied it by performing the first time-resolved structural transformation in the picosecond domain. It was the solid-liquid phase transformation of aluminium. Further work was conducted by Hani Elsayed-Ali, notably on surface melting. The activity was extended later to gas electron diffraction by Ahmed Zewail (Nobel Prize in Chemistry 1999). More recently – twenty years later – our picosecond electron diffraction experiment on aluminium was repeated by Dwayne Miller from the University of Toronto with a superior laser and shorter pulses. Note that Dwayne was at the University of Rochester in the chemistry department with a joint appointment in Optics when, in 1982, Steve did his seminal experiment. Today, time-resolved electron diffraction is becoming a very active field, rivalling time resolved x-ray diffraction.
First step of single cycle THz generation
We knew that the picosecond rise time produced by photoconductive switching could be used to produce THz transients, either from the gap itself by putting a switch in a coaxial waveguide transition or by exciting a microwave antenna. This simple experiment was performed by a dedicated undergraduate student, Daniel Blumenthal, from the electrical engineering department in collaboration with his adviser, Charles Stancampiano, and André Antonetti from the Ecole Nationale Supérieure de Techniques Avancées in France. The THz field became a very important domain once it was realised by Auston that the electric field could be time-resolved by the laser pulse itself. The field amplitude and phase could be measured, and a new THz spectroscopy technique was born that would replace infrared Fourier-transform spectroscopy. Besides spectroscopy, applications of these transients include THz imaging. Also, the methods of generation have been vastly advanced as demonstrated by X-C Zhang.
Electro optics sampling: measuring electrical signals with subpicosecond resolution
We could switch electrical signals with rise times in the subpicosecond domain, but it was difficult to measure them. Wide band sampling oscilloscopes could only go to 25 ps and the only way to measure the picosecond pulses was to use a second photoconductive gap with a fast photoconductive semiconductor. Of course, one solution was to try to use the electro-optic effect. The EO effect can have a purely electronic reaction with a sub-femtosecond response. But there is no free lunch, and this ultrafast response is paid for in terms of sensitivity. Kilovolts are usually necessary to detect a signal. So, it appeared the EO effect could not be a contender for fast measurements, as it was not sensitive enough. Janis Valdmanis, who had the idea to use lock-in detection in conjunction with the electro-optic effect, demonstrated this to be false. With his “golden hands,” Janis showed that sub-millivolt, subpicosecond signals could be measured. The EOS technique became an indispensable tool to visualise THz electrical signals. For the first time, direct propagation of picosecond electrical pulses on transmission lines, both normal and superconducting (with low and high-Tc) could be investigated. EOS was also used in the measurement of the fastest transistor rise times and the switching of Josephson junctions. It was also used in the direct investigation of subpicosecond carrier dynamics in semiconductors, such as velocity overshoot. Most of the activity was coordinated by D. Dykaar and involved many students, like J. Whitaker, visiting scientist Roman Sobolewski and Professor Thomas Hsiang, from electrical engineering, as well as Kevin Meyer, a student from physics.
Chirped pulse amplification
The generation and amplification of short pulses was, however, our main activity. Short pulses were used for everything. At that time, Ti:sapphire had not been invented, and dyes like rhodamine 6G were the main amplifier media. The leading laboratories were at AT&T Bell Laboratories with the group of Charles Shank, and with Erich Ippen and Hermann Haus at MIT. In our group, outstanding students were working on dye-based generation and amplification of ultrashort pulses. They were Theodore Sizer, Irl Duling, James Kafka and Theodore Norris. During one of our constant and endless discussions about novel ideas and concepts, we discussed in 1982 with Steve Williamson a possible way to get larger energy per pulse by using better energy storage media. Strangely enough, 1982 also marked the birth of our daughter Marie, which convinced me that I could do two very different things at the same time: generate a Nobel Prize-worthy idea and engender with Marcelle an adorable girl. From a bandwidth point of view, Nd:glass can in principle amplify subpicosecond pulses. However, unlike in dye, Nd:glass is almost too good of an energy storage medium. The major problem is that the pulse energy becomes too large, leading to high intensities and nonlinear effects. The nonlinear effects contribute to destroying the beam quality and ultimately lead to the “destruction” of the optical amplifier. Dyes, on the other hand, do not have this problem. They are mediocre energy storage media, due to their large amplifying cross-section. Therefore, the pulse energy stays below the critical intensity level where the nonlinear effects dominate. We were greatly influenced by the work of Dan Grischkowsky (IBM Yorktown Heights) and Anthony Johnson (AT&T Bell Laboratories) that demonstrated that by propagating a relatively long pulse in a fibre, the pulse will be the subject of broadening and stretching by a combination of self-phase modulation (SPM) and group velocity dispersion (GVD). As a result, the pulse is stretched with the spectral content of a much shorter pulse. It exhibits a linear chirp. At this point it can be compressed by using a Treacy grating pair, which exhibits a negative GVD to a value one hundred times the value of the input pulse. It looked to me that it would be simple to try to amplify the pulse in order to extract the amplifier energy and compress it later when the energy would be fully extracted. I asked a new student, Donna Strickland, if she would like to do this experiment. Donna was excited about it but also concerned that it might not be good enough for a Ph.D. thesis. She quickly demonstrated that this concept was working to the millijoule level.
It was at this time that Marcel Bouvier from Albertville joined the group. He was a shrew electrical engineer who made some impressive contributions. Notably by inventing a key device, called 1kHz Pockels cell that revolutionized the field. This laser component is now in the exhibit of the Nobel Museum. He also started the company MEDOX Inc. with Phillippe Bado a laser scientist in the group.
The key to CPA: the matched stretcher-compressor. The first approach to CPA was rudimentary and relied on an unmatched stretcher-compressor system. It was not perfect. After a certain amount of stretching, the compressor could not compress the pulse without causing significant wings on the pulse. The fibre-grating pair system was not matched over all orders. What we needed was a matched stretcher-compressor system so we could extract the energy better and compress it better. The matched stretcher compressor became our “Holy Grail.” I was continuously thinking about it. One day I was skiing at Bristol Mountain with my wife Marcelle, and on the chairlift, I started to think about a paper I read the day before from Oscar Martinez. This paper was describing a compressor for communication applications at 1.5 mm. At this wavelength the GVD in fiber is negative and the pulses exhibit a negative chirp where the blue frequencies lead the red ones. To recompress the pulse at the fiber output, Martinez proposed a compressor with positive GVD that was a combination of a grating pair and a telescope of magnification unity. I realised that the Martinez compressor in the positive GVD region was in fact the matched stretcher of the Treacy compressor. This was exactly what we were looking for. I interrupted my day of skiing and went back to the laboratory, where I met Maurice Pessot, a new student in my group. I asked Maurice to drop what he was doing and show that the Martinez stretcher and the Treacy grating pair were matched. In a beautiful experiment, Maurice showed that an 80 fs pulse could be arbitrarily stretched 1000 times by the Martinez device and recompressed by the same factor to its initial value. A major hurdle in CPA was overcome. Fifteen years later, this stretching-compression system is still part of the standard CPA architecture.
En Route to the Petawatt. The stretcher-compressor was integrated in our first Joule level Nd:glass system by a visiting scientist, Patrick Maine, and a post-doctoral fellow, Philippe Bado. With Donna they demonstrated a pulse with one joule in 1 ps., i.e. 1 terawatt on a table top – called the “Maine event” since. It was at night and we were jubilant. Robert McCrory, the LLE director, was as usual working late and heard our noisy celebration. He poked his head in the laboratory curious to know what was going on. I told him that we had just demonstrated the generation of one TW with a new amplification technique. It was a thousand times improvement in power over standard techniques, and moreover, this technique could be scaled to a much higher energy than the kJ level using the glass development laser (GDL), a prototype chain at LLE. At that time, we paused and asked ourselves what the next scientific prefix after “tera” was. Nobody knew. We went to Bob’s office and discovered that it was “peta.” So, from now on, our next goal would be the petawatt. The first article on the possibility of producing petawatt level pulses was described in a French scientific journal, “En Route Vers Le Petawatt” and the first petawatt pulse was demonstrated by Michael Perry at Livermore ten years later. At that time, we decided with Patrick and Donna to call this new amplification technique chirped pulse amplification (CPA). Of course, Wayne, who was at AT&T Bell Laboratories by that time and always has something to say, called me to argue that people would get the acronym mixed up with “certified public accounting.”
It was a great time with visits from bright people, like Michael Campbell and Michael Perry from LLNL who understood immediately the revolutionary nature of CPA. We had big plans to go together to the PW level. Also, we had See Leang Chin who came for a sabbatical and was the first to propose with Joseph Eberly to use T3 for the study of light matter interaction in the high intensity regime. With Henri Pepin and his group, Mohamed Chaker and Jean-Claude Kieffer, the contingent of Quebecois from INRS was growing. INRS would play an important role later in our decision to move to University of Michigan. Also, I don’t want to forget the group of Adrien Mellinos who had the first the idea of using T3 on SLAC to demonstrate pair generation on SLAC.
We worked a lot to extend the technique to other materials, such as Alexandrite with Jeff Squier and Don Harter. That was before Ti:sapphire. Alexandrite was at that time the only broadband high-energy storage material available. A lot of the CPA work continued after our move to the University of Michigan with Ted Norris, Jeff Squier, François Salin and Gary Valliancourt producing the first kHz Ti:sapphire source – the workhorse of many ultrafast optical laboratories today. Let’s also not forget Marcel Bouvier, our indispensable and reliable electrician.
However, by inventing CPA we created a new field with characteristics diametrically opposed to the fusion field, the LLE main mission. Our success was highly appreciated but it created some tension. One day I received a call from Duncan Steel and the dean of the College of Engineering from the University of Michigan, Charles Vest, inviting me to move all my group and their families to the University of Michigan Ann Arbor. After one month of negotiation, in August 1988, my group moved to Michigan. This coup was apparently perceived very positively by the MIT search committee looking for a new president. A few months later, Chuck Vest became President of MIT, a position that he held for 16 years. With me, Henri Pépin’s group followed with their equipment. They were the initiator of the ultra-high intensity field at Michigan.
In 1990, two years after our arrival we had been able to attract prominent scientists/professors like Janis Valdmanis, Donald Umstadter and Philip Bucksbaum from Bell Labs. We responded successfully to a call from the Natrional Science Foundation to build an NSF Center. We named it the Center for Ultrafast Optical Science (CUOS) based on femtosecond optical pulses that can provide the shortest controlled bursts of energy, yet produce and enable the highest laboratory peak-power densities ever generated. These two characteristics have opened access to a number of new fields of research not previously available to basic science and applied technology. In the original establishment of the Center, it was pointed out that “ultrafast optical science is an inherently interdisciplinary effort implying scientists and technologists working on laser and optical physics, atomic and condensed-matter physics, chemistry, optical fibres, and electronics.” The first important results on high field physics in gas and solid were obtained by the group of Don Umstadter and J.C. Kieffer with high energy electrons acceleration … It was at CUOS in the early 1990s thanks to M. Bourier Pockels cell the kHz Ti: Sapphire was demonstrated by Jeff Squier and François Salin. This system became the workhorse of femtosecond research. As I was presenting in Bayreuth the kHz laser, Georg Korn introduced himself and expressed the desire to come to CUOS. I accepted and Georg stayed a few years with us where he participated in many important experiments. CUOS now includes researchers in all fields, as well as in plasma physics, accelerator physics, materials science, biophysics, and medicine, all working closely with scientists developing new ultrafast laser sources and measurement techniques – in short, in a “centre mode” of research.
In 1994, we spent 4 months on sabbatical at the University of Tokyo Roppongi at the laboratory of Shantaru Watanabe. We enjoyed immensely the time in Japan. We were hosted by Professor Hiroshi Takuma. It gave me also the opportunity to meet Professor Toshiki Tajima, the inventor of the wake-field accelerator, whom I did not know before. It was an epiphanic moment that started a fruitful collaboration between us that has had few discontinuities since. Marcelle started to take some Ikebana classes and later became a sensei of the SOGETSU Ikebana school.
Femto-micromachining and eye surgery
Ultrashort laser pulses offer both high laser intensity and a precise laser-induced breakdown threshold with reduced laser fluence. The ablation of materials with ultrashort pulses has a very limited heat-affected volume. The advantages of ultrashort laser pulses are applied in precision micromachining of various materials. Ultrashort-pulse laser micromachining have a wide range of applications where micrometer and submicrometer feature sizes are required.
With Ron Kurtz, Tibor Juhasz and students, we investigated refractive cornea surgery in vitro and in vivo by intrastromal photodisruption using a compact ultrafast femtosecond laser system. Two students, Detao Du and Xinbing Liu, demonstrated that in the femtosecond regime, photodisruption is associated with smaller and very deterministic threshold energy as well as reduced shock waves and smaller cavitation bubbles than with nanosecond or picosecond lasers. Our reliable all-solid-state laser system was specifically designed for real world medical applications. By scanning the 5 micron focus spot of the laser below the corneal surface, the overlapping small ablation volumes of single pulses resulted in contiguous tissue cutting and vaporisation. Pulse energies were typically in the order of a few microjoules. Combination of different scanning patterns enabled us to perform corneal flap cutting, femtosecond-LASIK, and femtosecond intrastromal keratectomy in porcine, rabbit and primate eyes. The cuts proved to be highly precise and possessed superior dissection and surface quality. Preliminary studies show consistent refractive changes in the in vivo studies. We conclude that the technology is capable of performing a variety of corneal refractive procedures at high precision, offering advantages over current mechanical and laser devices and enabling entirely new approaches for refractive surgery.
Back to France
In 2004 I was invited for the scientific evaluation of the Laboratory of Applied Optics (LOA). I was approached by the research director of the École Polytechnique, Maurice Robin, who asked me about the possibility of returning to France. Although I was very happy at Michigan with CUOS, it was an excellent opportunity for us to come back and almost 30 years later I returned as the director of the LOA in 2005.
The same year, ESFRI was in the process of updating its roadmap of large-scale research infrastructures. I took advantage of the opportunity to propose the Extreme Light Infrastructure (ELI) as a Pan-European facility. At the same time the Ile-de-France region also had a call for major instruments and so we proposed the Apollon laser facility as well. These laser facilities, for me, were the extension of the ultra-high intensity at CUOS by seeking the tens of PW level almost 100 times more powerful than the Hercules laser at CUOS. It was a beautiful opportunity to fulfill our dream with Tajima. We succeeded in obtaining both projects. I was the initiator and PI of the ELI Preparatory Phase that started in 2008.
After an agonising debate between the École Polytechnique, CEA, CNRS and the Institute d’Optics, it was decided to build the Apollon laser at the CEA site at L’Orme des Merisiers in an old accelerator facility that had been dismantled. It was decided also that the LULI would build and run the facility by 2019–2021.
The ELI project has as its goal to build an infrastructure of facilities providing the most advanced peak power laser systems in the world. This gargantuan power will be obtained by producing kJ of power over 10 fs. Focusing this power over a micrometer size spot, will bring forth the highest intensity. By producing, firstly, the highest electric field, secondly the shortest pulse of high energy radiations in the atto/zeptosecond regime and thirdly, electrons and particles with ultra-relativistic energy in the GeV regime, the laser signalled its entry into Nuclear Physics, High Energy Physics, Vacuum Physics and in the future Cosmology and Extradimension Physics. More precisely, ELI will be the first infrastructure dedicated to the fundamental study of laser-matter interaction in the ultra-relativistic regime (I > 1024 W/cm2). The infrastructure will serve to investigate a new generation of compact accelerators delivering energetic particle and radiation beams of femtosecond (10−15 s) to attosecond (10−18 s) duration. Relativistic compression offers the potential of intensities exceeding greater than 1025 W/cm2, which will challenge the vacuum critical field as well as provide a new avenue to ultrafast attosecond to zeptosecond (10−21 s) studies of laser-matter interaction. After long debate it was decided that ELI will have three pillars located in three European emerging countries. Each countries will work on coordinated different topics: Czech Republic for the development of high energy particle radiation Beam Line, Hungary for Attosecond Source and Romania for Nuclear Physics.
In 2010, following the advice of Alexander Sergeev, I applied for a Russian Megagrant and was one of the winners. I had a joint appointment between the Institute of Applied Physics at Nizhny Novgorod and the University of Nizhny Novgorod. We were housed in a studio next to Sacha and Marina sharing our breakfast and meals together. We had long and friendly discussions between us on all subjects, sometimes exposing our French and Russian differences. Our collaboration started with the Russian Excel Laser and still continues with fine scientists like Efim Kazhanov and Sergey Mironov.
IZEST: orbital debris, going beyond the horizon
For ELI, 2011 was the end of the preparatory phase and the beginning of the construction phase. The respective countries managed the three facilities. I was 67 and had to become professor emeritus. With Toshiki Tajima, we proposed to create a unit to explore the prospective for Extreme Light, IZEST for International Zeptosecond Exawatt, Science and Technology. IZEST is devoted to the investigation of Extreme Light beyond the Horizon set by the ELI infrastructure.
Among IZEST’s achievements, we note: The International Coherent Amplification Network (ICAN) project, a laser system characterised by a novel architecture, based on the coherent combination of many CPA fibre lasers. ICAN, provides the laser with high peak power, high average power and good wall-plug efficiency. This is paramount to applications such as particle colliders, nuclear waste transmutators and space debris mitigation. The development of the working prototype is the XCAN program and is directed by Jean-Christophe Chanteloup.
After seeing the movie “Gravity”, it occurred to me that the ICAN system could play a key role in space debris mitigation. The first conceptual demonstration was made by Rémi Soulard and Mark Quinn.
Finally, my future goal is dedicated to the increase of peak power towards the Schwinger regime. Here with Toshiki Tajima and Jonathan Wheeler, we are aiming to test a new paradigm: instead of producing high peak power by increasing the laser energy, we will increase the peak power by shortening the laser pulse to the atto and subattosecond regime. In this way we could produce high energy, attosecond single cycle pulses in the x-ray regime. The peak power could be exawatt, the wavelength in the x-ray and the intensity in the Schwinger regime, enough to produce PeV particles and vacuum materialisation.
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/ Nobel Lectures/The Nobel Prizes. The information is sometimes updated with an addendum submitted by the Laureate.
See them all presented here.