Over the past two decades there has been a significant growth across the world in the abundance of laser facilities capable of producing peak powers on the order of petawatt (PW) levels. In these systems, for a fleeting moment, a laser pulse can be produced that has an instantaneous power that dwarfs the global electricity supply, which can be focused to power densities about 22 orders of magnitude greater than sunlight. Consequently, any matter that the laser interacts with is rapidly subject to extreme change, generally becoming transformed into its fourth state—plasma. Depending on the configuration of the interaction, a diverse range of science and applications emerge from this extreme environment.
This section contains a review of high-power petawatt-class systems globally. There are many high-power laser systems and facilities, and for clarity and the purposes of this survey a cut off is applied below 0.5 PW. A comprehensive list appears at the end of the chapter. The review is organized by laser technology class, as in general this also provides a natural demarcation between the science and applications that can be accessed. Finally, a distinction is made between systems that are currently in existence and operational, systems that are under construction (i.e., funded), systems that are not yet funded but are clearly and formally defined by the report and the national roadmap, for example, and finally other systems that are aspirational in character.
Given the scope of research made possible by PW-class lasers, there are a number of large-scale facilities internationally that host such systems. At the time
of writing, there are over 50 PW-class lasers worldwide in operation, under construction, or in the planning phase. A comprehensive description of these facilities at the end of 2015 was published by Danson et al.1 These range from smaller commercial systems that can fit into a large laboratory up to building scale systems like the National Ignition Facility (NIF) in the United States.2 The global spread of these facilities is shown in Figure 4.1, which shows a record of systems identified by the International Committee for Ultra-Intense Lasers (ICUIL), an Organisation for Economic Co-operation and Development (OECD) sub-committee, and their host facilities on a world map. A detailed discussion of worldwide petawatt-class facilities is given in Appendix E.
Attaining high peak power relies on the correct combination of two properties—energy and time—specifically, a high energy laser pulse delivered over very short time scales. This is the essence of a high-peak-power laser, whether designed to generate tens to millions of Joules of energy in a pulse that is femtoseconds to nanoseconds long. The application and relevant science depends heavily on the exact nature of the parameters of the laser and the geometry of the interaction; the number and scope of applications are many and are described in Chapters 5 and 6.
The introduction included Figure 4.1, the ICUIL world map, which shows the broadly global distribution of high-power laser facilities and research centers. A more informative representation of Figure 4.1 shows the global, aggregated distribution of peak power that is currently either operational or under construction. It is clear that significant concentration occurs in Europe, owing principally to the self-organization of the various institutes and countries involved via European Union programs that have supported and brought a strategic aspect to the field over several decades. The United States is notably behind. The full listing of the PW-class systems and their key parameters are included at the end of this review in Appendix E.
If one considers systems that are planned, in the sense that they are at an advanced stage of definition and appear in (inter)national road maps or from major (inter)national infrastructures, etc., then the general position globally does not change significantly. This is reflected in Figure 4.2.
The leading position, in terms of total peak power, currently held by the European countries has developed only recently. In fact, if one looks at the growth
1 C. Danson, D. Hillier, N. Hopps, and D. Neely, 2015, Petawatt class lasers worldwide, High Power Laser Science and Engineering, 3: e3.
in the number of operational PW-class laser systems by date (see Figure 4.3), the United States has been superseded by Asia and Europe only in the past 2 years. This is due to a rapid increase in the number of systems under construction in these regions, while the United States has remained level since 2012. This has not stopped the global trend showing significant growth in the number of systems—the dashed line in Figure 4.3 shows the continuation of this growth by systems that are planned but that currently have no published completion date. Again, here there is a sharp increase in the number of systems within Europe.
To more clearly see the number of systems coming online, Figure 4.3 shows the number of systems brought online each year by North America (green), Europe (blue), and Asia (red). Systems that are expected to be operational beyond 2020 or whose completion dates have not been published are combined in the TBD column. This graph shows that initial development of PW-class lasers was dominated by North America in the mid-2000s, but that this lead has slowly shifted towards Asia and then Europe in the present day and up to 2020. Even if one includes systems that are only proposed, North America is notably behind.
At the time of writing, North America has 9 PW-class systems either operational, under construction, or planned; Asia has 12; and Europe has 32. The
significant increase in development within Europe can be broadly attributed to key European-wide projects such as the Extreme Light Infrastructure (ELI)3 and Laserlab.4 (See Figure 4.4) These projects and others like them will be discussed in more detail in Section 4.3.
Changing focus to the distribution of PW-enabling technology within each major region shows another difference between North America and Europe. Figure 4.5 is a compilation graph that shows the number of systems in each region and the technology used for the main amplifier (refer back to Chapter 2 for the main technology types) and their respective numbers. For example, North America is shown to have 9 PW-class systems operational, under construction, or planned. Of these 9 systems, 4 are glass-based; 3 are Ti:Sapphire-based, 1 is a megajoule system, and 1 is based on the optical parametric chirped-pulse amplification (OPCPA) technique. This shows a heavy weighting towards the older glass-based technol-
ogy compared to the newer Ti:Sapphire technology, and only one planned system utilizes the latest OPCPA technology. In contrast to this, the distribution of technologies within Europe is large. The most common type is Ti:Sapphire, but there are a number of operational/under construction or planned OPCPA and diode systems. The diverse range of technologies in development highlights the fact that PW-class laser development has garnered much support within Europe and that funding exists to further develop and exploit these new technologies.
The substantial growth of PW-class OPCPA systems over the coming years compared to other technologies is highlighted in Figure 4.6, which shows the peak power versus operational date of all systems included within this review. Each system is represented by a symbol representing its main technology type: glass (diamond), Ti:Sapphire (triangle), OPCPA (square), diode-pumped (cross), megajoule (circle), and fiber (plus). Additionally, the status of the system is indicated by color: decommissioned (black), operational (green), under construction (orange), and planned (red). This somewhat complicated graph contains a strong message;
the technology of choice for PW-class systems is changing from the original glass systems, through the established Ti:Sapphire systems, toward OPCPA systems, which enable much higher peak powers.
In addition to the move toward OPCPA-based technology there has, in recent years, been a concerted effort to increase the average power and hence repetition rate of large-scale facility lasers, with the aim of developing new areas of application for the unique sources produced. This trend towards higher average powers is illustrated in Figure 4.7, which shows the expected operational dates for the Ti:Sapphire lasers in this review with a repetition rate of > 1 Hz. All but two use flash lamps as the primary means of optically pumping the system.
One of the most important recent technological advances in this area is the use of diode laser pumping architectures. Here, efficient diode pump lasers replace inefficient flash lamps that generate large amounts of excess thermal energy, which must be removed or managed. The highest repetition rate that has been achieved using traditional flash-lamp technology is the Advanced Laser Light Source (ALLS)
in Canada. This system operates at 0.5 PW at a repetition rate of 2.5 Hz,5 with diode-pumped technology opening an enhancement path to 10s of Hz, although commercial systems at slightly less power and higher repletion rate are available.
In terms of diode-pumped Ti:S systems, there are only two systems currently planned or under construction in the world—the ELI Beamlines L3 laser,6 which is being constructed by Lawrence Livermore National Laboratory (LLNL) in the United States, and the 10 Hz PW system currently planned for construction by the CLF in the United Kingdom. At its current schedule, L3 is likely to be operational for users in 2018. In the United Kingdom, Rutherford Appleton Laboratory (RAL) has developed a diode-pumped solid-state laser (DPSSL) system called DiPOLE (100 J @10 Hz)7 as a Ti:S driver and has a planned project PULSAR to establish a 10 Hz PW capability. All other Ti:S systems that operate at 1 PW or above have repetition rates limited to 1 Hz or lower.
The Extreme Light Infrastructure (ELI; Figure 4.8) is a unique development, scientifically, technologically, strategically, and politically. It is a large scale international laser infrastructure of approximately $1 billion capital cost that is being constructed in the European Union, made possible via the use of European Regional Development Funds (ERDF). It boasts a technical specification that is beyond anything that currently exists.
ERDF - Historically, ERDF have been used to support public infrastructure development such as roads, railways, airports, etc. throughout the European Union, but the application of ERDF to scientific infrastructure, while always possible, had never been used before. ELI fundamentally changed that and furthermore developed a truly unique implementation plan that has seen the physical infrastructure actually constructed in three different Eastern European countries—The Czech Republic, Hungary and Romania. These so called “pillars” of ELI despite being located in different physical locations will be operated as if they were a single entity via an EU device known as a European Research Infrastructure Consortium (ERIC). A 4th pillar, a 200 PW capability, was identified at the time of its proposal but its implementation has been held until a sufficiently robust technological basis
5 Advanced Laser Light Source, Canada, “Specialized Labs and Equipment,” https://navigator.innovation.ca/en/navigator/advanced-laser-light-source-alls, accessed January 30, 2017.
6 B. Rus, P. Bakule, D. Kramer, G. Korn, J.T. Gren, J. Novak, M. Fibrich, et al., 2013, ELI-Beamlines laser systems: status and design options, Proc. SPIE 8780: 87801T.
7 P.D. Mason, M. Fitton, A. Lintern, S. Banerjee, K. Ertel, T. Davenne, J. Hill, et al., 2015, Scalable design for a high energy cryogenic gas cooled diode pumped laser amplifier, Applied Optics 54(13): 4227-4238.
for its development exits. Opportunities for U.S. involvement in the fourth pillar depend on future investments as discussed in Section 7 of the report, particularly Conclusions 6 and 7 and Recommendations 3 and 4.
ERIC - The ERIC is a form of intergovernmental agreement among EU nations, enshrined in European law, that has been specifically developed to support pan-European research infrastructures, where arrangements are needed that transcend national boundaries. Traditionally this has required specific inter-governmental agreements or treaties to be individually developed, negotiated, and enacted, which is a time consuming and cumbersome process. As an international organization, ERIC has its own legal personality and enjoys a number of significant benefits. A pre-cursor organization, known as the ELI Delivery Consortium (ELI-DC) has been created to establish the ELI-ERIC and to secure the necessary financial backing from the various EU member states interested in participating in ELI-ERIC. Currently the membership of ELI-DC stands at CZ, RO, HU, IT, DE, FR, and the
UK. The legal status of an ERIC allows for the participation of non EU countries as members (that would have to accept the jurisdiction of the European Court of Justice), and the individual statues of any ERIC can allow for partnerships with non EU countries. ELI is due to come online to users from around 2018.
ELI in many ways is the product of the many coordinating actions of the European Commission, which over a series of “Framework Programs,” including the ESFRI Roadmap, structured the research landscape in Europe. These programs promoted cooperation, interconnection, and mobility of people, which led progressively to a more strategic character in the way scientific communities formed and acted. The history of high power laser research in Europe is a prime example of this European cooperative strategy.
Estimating the scientific productivity of the field, and indeed the size of the scientific community involved, is a challenge as there are no centralized records that can be consulted. This study has estimated the size and productivity of the community of interest using Web of Science (WoS)8 using various search terms in an attempt to provide some general indication. A full listing of the search terms and the method used for the search is described in Appendix C1.
The search resulted in approximately 21,000 publications spanning 45 years and contributed by 91 individual countries. The number of publications released per year was very low up to 1990, when publications in the field of PW-class lasers began to climb significantly each year. This coincides with the development and commissioning of the first PW-class facility, Nova, as shown in Figure 4.9. The yearly increase in publications in this field is continuing to grow, in line with the number of operational facilities.
There are three continents that have contributed to the vast majority of publications in the field; these are North America, Europe, and Asia. However, if one separates this search down to individual countries, as shown in Figure 4.10, then the United States is shown to be the most active single country in terms of total number of publications. The percentage shown is the fraction of publications that include at least one author from that country. For example, if a publication has two authors from the United States and one from the United Kingdom, both countries get a single point for this publication. The United States has authors on 28 percent of all publications within this search, more than twice that of Germany, the second highest publisher.
8 Clarivate Analytics, “Web of Science,” http://ipscience.thomsonreuters.com/product/web-of-science, accessed January 30, 2017.
Due to the complication of duplicates from individual countries within a continent, it is not possible to extract meaningful data on the continental distribution of publications from this particular search.
From a facility perspective, there are over 2,000 organizations that have an author within this search. The total number may be somewhat lower due to misspelling, but this, coupled with the fact that 91 countries appear in this search, shows the global reach of the user community in this field. Of the organizations, the top 15 are shown in Table 4.1 for reference. As with the countries, these are facilities that have at least one author on a paper. Again, one can see that the United States and its facilities and departments appear high on this list. The “enhanced” organizations list is produced by combining results which appear to be same institute (i.e., change of name or same postcode given).
What this data shows clearly is that while North America does not have the same diversity or number of PW-class facilities as Europe or Asia, the United States is producing a proportionally large number of publications in this field, highlighting how active the user community here is. If this interest from the user community
TABLE 4.1 The Top 15 Organizations within the Publications Search, the Number of Publications with Associated Authors, and Their Percentage of the Total Number
|Organizations (Enhanced)||Number of Records||% of Total|
|UNITED STATES DEPARTMENT OF ENERGY DOE||1677||7.773|
|CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS||1046||4.848|
|RUSSIAN ACADEMY OF SCIENCES||999||4.63|
|LAWRENCE LIVERMORE NATIONAL LABORATORY||945||4.38|
|CHINESE ACADEMY OF SCIENCES||824||3.819|
|UNIVERSITY OF CALIFORNIA SYSTEM||768||3.56|
|UNIVERSITE PARIS SACLAY COMUE||666||3.087|
|MAX PLANCK SOCIETY||487||2.257|
|STFC RUTHERFORD APPLETON LABORATORY||391||1.812|
|UNITED STATES DEPARTMENT OF DEFENSE||355||1.645|
|PIERRE MARIE CURIE UNIVERSITY PARIS 6||355||1.645|
|CZECH ACADEMY OF SCIENCES||334||1.548|
SOURCE: WoS analytics.