We are 60! Free

To say that APL is my home journal is by no means an exaggeration. I started subscribing to APL in the late 80s while I was doing postdoc at Berkeley. I believe that I have browsed through almost every issue since then (thankfully, I have been receiving the hard copies for free since 2003). This habit has helped me to stay informed in the large field of applied physics. I still remember vividly when I was offered a faculty position in the MIT EECS Department, the EE Associate Department Head told me that the department was not hiring someone only working on superconducting devices (that was my entire research career by then), but an “Applied Physicist.” That departmental wish perfectly aligned with my own research plan. I did my Ph.D. research on Josephson junctions, focused on basic physics. My postdoctoral research was on quantum-limited superconducting heterodyne receivers, which naturally dealt with the applied aspect of physics and also involved heavy engineering. Going forward from there, my inclination was to choose projects with a strong physics flavor but with potential applications. Looking back over more than three decades, that has been the pattern of my research career.

With the focus on applied physics and developing novel devices based on new physics, APL naturally became the journal of many of my key publications. Back in 2003, MIT EECS Department was celebrating its centennial (after a group of physicists was kicked out of the Physics Department 100 years ago because their work was considered too applied, this group formed an EE Department that instantly became the largest one in MIT). A book came out of this centennial celebration. At its end, each of the >120 faculty member was asked to list a single publication that he/she considered the most impactful. Coincidentally, our group just developed terahertz quantum cascade lasers (THz QCLs) based on resonant phonon scheme, and that APL paper¹ was my natural choice for the centennial book. After that breakthrough, rapid-fire developments followed and several of them were published in APL.^2–4 

With so many of my key papers published in APL, after the promotion to full professor, I decided to return the favor to the journal. At the time, my colleague—the late Prof. Millie Dresselhaus—was the President of the American Institute of Physics (AIP), so I expressed to her my interest to volunteer my service to APL. Shortly after, Nghi Lam, the Editor-in-Chief (EiC) of APL at the time, invited me to join the editorial board of APL/JAP and I served for the term of 2003–2006. At the end of my term, Nghi invited me to become an Associate Editor working in the trenches. I happily accepted the invitation. The journal then was transitioning to electronic version, and I may be the first remote editor hired during this transition. In 2014, Reuben Collins (Nghi's successor) convinced me to take on a larger role of Deputy Editor, which has been my role to this day. As a reader, author, editorial board member, and Associate/Deputy Editor, I wholeheartedly say happy birthday to APL on its 60th birthday. It has made a huge impact in the field of applied physics, and it will continue to do so indefinitely.

Quantum Cascade lasers (QCLs), a field that Deputy Editor Qing Hu has been so instrumental in developing, have remained a critically important area of technology in the intervening years. QCLs operate in the mid-IR and THz region of the spectrum and sources play an important role for areas such as biological sensing, trace gas spectrometry, and industrial process control. APL remains the journal of choice for leading papers in QCL research including those from Qing Hu himself. See, for example, his paper on split-well direct phonon THz QCLs⁵ and examples such as thermoelectrically cooled QCLs operating at 210 K,⁶ room temperature surface emission on large area photonic crystal QCL,⁷ narrow linewidth characteristics of power efficient mid-IR interband cascade lasers⁸ route to carrier leakage suppression for high power QCL operation,⁹ THz¹⁰ and mid-IR frequency combs,¹¹ theoretical treatment of double longitudinal intra-well depopulation,¹² properties of rf mounted interband cascade lasers,¹³ high responsivity quantum cascade detectors,¹⁴ electroluminescence from Ge–SiGe quantum cascade structures,¹⁵ and last but not least external cavity QCL with graphene opto-electronic mirror.¹⁶ These papers demonstrate that QCL research remains a vibrant area of applied physics research that is of high relevance to a number of societally important technologies. Looks like an area ripe for a new special topic collection.

APL's 60th Anniversary gives me the occasion to reflect on its 50th Anniversary, when I also had the privilege to be a member of APL's editorial team and to realize what a difference 10 years makes. APL's 50 years were celebrated by an evening symposium at the Fall 2012 MRS Meeting in Boston in which distinguished representatives of seven especially topical fields were invited to give a presentation “covering the progression of their field in general with some specific examples of APL articles that had impact in modern technologies.” The topics in question were as follows:

• Luminescent Nanoscale Silicon (Leigh Canham, Birmingham, UK)

• Bandgap Engineering, Quantum Cascade Lasers, and Wavefront Engineering (Federico Capasso, Harvard)

• The Light Emitting Diode (Russell Dupuis, Georgia Institute of Technology)

• Programming Nanoscale Assembly (Oleg Gang, Brookhaven)

• Glassy Metals (William Johnson, California Institute of Technology)

• Metal Spintronics (Stuart Parkin, IBM Almaden)

• Organic Electronics (Ching Tang, Rochester)

Like everything else in the world, applied physics has evolved dramatically over the last 10 years, and the choice of topics for such a symposium today would look very different as well as our gender and geographic representation. To meet the considerable changes in science and the scientific publishing landscape, APL has seen many developments since 2012. The page limit has been dropped in favor of a 3000-word limit, the review process has been made more rigorous with acceptance now predicated on two positive recommendations, and the categories in which authors suggest to place their papers has evolved considerably, with the titles changed to emphasize current scientific directions and two new items added in January: Phononics, acoustic and thermal properties, and metasurfaces and metamaterials.

As a result of these developments, the quality of the journal continues to rise. Thanks to its vigorous community of authors and reviewers, APL can look forward to being a major player in the world of applied physics for the next ten years and beyond.

I joined Applied Physics Letters as an Associate Editor in January 2020, and I enjoy applying my interdisciplinary research experience in this role. A solid-state physicist by training, I spent my Ph.D. and early postdoctoral research career investigating semiconductor nanostructures (quantum wells and quantum dots) in the coherent nonlinear light–matter interaction regime. Realizing that the instrumentation involved in those experiments had much in common with multiphoton microscopy for bioimaging, and with a passion for developing novel technologies, in 2004 I started switching my research direction toward biophotonics. The development of innovative optical microscopy technologies for bioimaging is an area gaining increasing attention within the Applied Physics Letters community, and I am pleased that our 2008 paper on coherent anti-Stokes Raman scattering (CARS) microscopy¹⁷ contributed significantly to the field. Upon joining the CARS community, we soon realized the importance of simplifying microscope setups to facilitate their widespread use in the life sciences. To that end, we designed a method whereby broadband femtosecond laser sources, commonly used in, e.g., two-photon fluorescence microscopy could also provide a spectrally narrow CARS excitation, using glass blocks of known group-velocity dispersion to chirp pulses in a simple and efficient way.¹⁷ It is exciting to see that this idea has been taken up by many labs and is applied not only to CARS but also stimulated Raman scattering (SRS) microscopy.

When looking at the list of recently published works, I find particularly interesting the paper entitled “How many photons does it take to form an image?,”¹⁸ which addresses a fundamental question in imaging. The authors offer a short perspective, ranging from using quantum states of light to adopting machine learning approaches. These are fascinating considerations, and their application in the context of biophotonics is highly appealing.

As an Associate Editor for Applied Physics Letters, I manage manuscripts across several sections in biophysics, interdisciplinary physics, semiconductor materials, and photonics. I have particularly enjoyed the “brainstorming” discussions in the Editor's meeting days, where we can suggest new special topics and launch new sections. It is exciting to be able to support scientific dissemination of the highest quality in such an editor role, and I was pleasantly surprised by the creative process in it. I am very much looking forward to next steps in this journey.

Paola has also been instrumental in suggesting the special topic collection in Advances in Optical Microscopy for Bioimaging, open for paper submission until 30 September 2022.

Hongping Zhao has been an Associate Editor with APL since 2016. In the last few years, she has suggested three exceptionally successful special topic collections associated with the emerging area of wide bandgap semiconductors.

See Ultrawide bandgap semiconductors, which closed September 2020; Wide- and ultrawide-bandgap electronic semiconductor devices, which closed January 2021, and Ultraviolet and deep-ultraviolet light emitters, which has just launched for submissions. Here, Hongping talks about the first of these special topics and the papers in the collection.

Ultrawide bandgap (UWBG) semiconductor materials and devices are considered as the building blocks for next-generation electronic, optical, sensing, and quantum device technologies. Advancements in the field evolve rapidly that require prompt dissemination of research findings. Known for rapid publication of new experimental and theoretical papers in applied physics, APL launched the Special Topic on “Ultrawide Bandgap Semiconductors” (UWBG) in 2020, with the support from the external guest editors, including Drs. Masataka Higashiwaki, Robert Kaplar, and Julien Pernot.¹⁹ This Special Topic attracted the submissions of about 200 manuscripts with three representative UWBG material systems: AlGaN and related UWBG nitrides, gallium oxide (Ga₂O₃) and alloys, and diamond. More than 20 papers published on AlGaN considering the growth, crystal structure, doping, and defects of AlGaN; AlGaN/GaN-based high electron mobility transistors; and AlGaN-based UV LEDs and laser diodes. Studies of UWBG nitrides other than AlGaN, such as BAlN and ScAlN, are also reported. Over 40 papers on Ga₂O₃ are reported in this Special Topic, covering a broad spectrum of novel epitaxial growth technologies (molecular beam epitaxy, metalorganic chemical vapor deposition, and halide vapor phase epitaxy) of Ga₂O₃, defects and doping in Ga₂O₃ and AlGaO, and Ga₂O₃-based field effect transistors (FETs) and diodes. Fifteen original papers dealing with research challenges on diamond are reported, including the realization of large size diamond substrates, defects, doping and charge transport in diamond, and diamond-based FETs. The collection of articles captures the recent advancements in UWBG materials, physics, and devices, serving as a platform to stimulate more research interest and thus further advancements in the field. I would like to take this opportunity to thank all authors for their submissions to this special topic as well as all reviewers for their tremendous efforts and time.

I am one of the new faces in the editorial team, but I have been a reader and author of APL since the beginning of my scientific career in spintronics. It was, therefore, with great enthusiasm that I joined the team in 2021, to experience what it is to be on the other side of APL. It was a great pleasure to discover how close the editorial team is to the real research world. All decisions are taken by active scientists who understand what it is to be a young Ph.D. student or PostDoc who, like me, has often spent more time than I care to admit refreshing the “article-status” page of the submission website.

In terms of the scientific milestones that have been communicated to the scientific community through APL in 60 years, there is obviously plenty to talk about. I will choose to mention one paper that came out when I was busy being an 11-year-old girl but was going to define the start of my career in spintronics many years later: “(Ga,Mn)As: A new diluted magnetic semiconductor based on GaAs.”²⁰ (Ga,Mn)As is one of the most well-studied ferromagnetic semiconductors because it provides an exceptional playground for physics enabled by the existence of hole-mediated ferromagnetism. Bringing together semiconductor properties and magnetism was, and still is, of enormous technological interest, and (Ga,Mn)As presented an exciting path toward linking charge carrier density and ferromagnetism. The observation and study of the link between carrier density and magnetism in (Ga,Mn)As gave a boost to the quest for efficient gating of magnetism in spintronics devices. The paper has been, and continues to be extremely influential to the spintronics community with over 3000 citations and is part of the “classics” paper collection from APL and well worth a read. Today, electrostatic and ionic gating of magnetism in nanostructured metals constitutes a fast-developing field with promising perspectives for energy efficient spintronics, for which APL has just launched a dedicated special topic.

As an editor, I'm excited to have the privilege and the responsibility of handling some of the potential APL classics of the future. As an author and reader, I hope APL will continue bringing excellent science and innovation to the spotlight for many more years to come.