I first met Angus (Fig. 1) in the U.K. in 1990 through his daughter Eleanor. Right off the bat, Angus and I shared a common interest in physics, engineering, and software. Eleanor and I were married in 1991 and what had started as a great personal relationship between Angus and me shifted into a professional collaboration very shortly thereafter. Angus possessed a unique combination of intelligence, kindness, and empathy, and he had a killer sense of humor. He had a knack for remembering a multitude of interesting anecdotes and facts that he could call upon at any given moment. He was a terrific business partner in every way—so giving and generous with his time and his knowledge. His personality determined the core values with which he ran, and with which we still run, Thin Film Center. To me, personally, Angus was a father, a teacher, a colleague, and a friend. His legacy is vast. In the next few pages, I will do my best to identify the enormous contributions that Angus made to the field of thin-film optics over the course of his extraordinary lifetime.

 

Fig. 1. Professor Angus Macleod at home in 2007.

Download Full Size | PDF

Angus was born on 20 June 1933, in Glasgow, Scotland, the elder son of Dr. John Macleod and his wife Agnes. His childhood was a very happy one. He grew up with a younger brother, John, and dog Coco (a cocker spaniel) in Stoneyetts, just outside of Glasgow. Angus was a diligent student who enjoyed learning from a very young age. According to Angus, “John was the fun one and I was more serious and hard-working.” Angus completed his secondary education at the Lenzie Academy in Glasgow, and it was Lenzie that gave him his first introduction to physics. His interest was piqued, and he went on to study Natural Philosophy (now physics and astronomy) at the University of Glasgow where he was awarded an honours degree in 1954.

After completing his degree, Angus relocated to the south of England and joined Sperry Gyroscope in London, where he worked as a graduate apprentice. The graduate apprentice program gave students experience in practical skills that were not always taught at universities, and in this environment, Angus thrived. He was one of few people at Sperry to be working on complex problems of vibration and nutation because of his solid understanding of rigid body dynamics. At that time Angus lived in a room in a boarding house close to his work, and at a weekend badminton match he met Ann, a seasoned badminton player whom he fell for immediately. The two were married in 1957, and their first baby, Hugh, came along in 1959.

By 1960 Sperry Gyroscope was facing an uncertain future so Angus began the search for a new job. He applied for and landed a position with Williamson Manufacturing Company—an optics company well-known for high-altitude reconnaissance cameras and survey cameras. Within Williamson’s Angus created and headed up an advanced design and production facility which immersed him in the world of optical systems design. It was during this period that Angus first worked with interference filters, and it was here that he came across Oliver Heavens’ book, The Optical Properties of Thin Solid Films, which would prove invaluable in future endeavors.

In early 1963 Angus took an opportunity to join Mervyn Instruments, a small company whose employees referred to themselves as “manufacturing physicists.” Mervyn’s had recently won a bid to build a leak detector for the British Army: they were looking for something that could check the sealing of their electronic equipment. What was needed, in essence, was a nitrous oxide gas analyzer. One morning at work Angus found himself literally being handed a 12-inch vacuum chamber with nothing in it and was told to use it to make interference filters. Fortuitously for Angus, Oliver Heavens (Olly) was based just down the road at the Royal Holloway College, so Angus took full advantage and arranged a meeting. Once reassured that his ideas were correct, Angus drew up plans to turn the vacuum chamber into a coating machine for manufacturing infrared multi-cavity filters. Production was successful, and Angus’s thin film career was launched.

In 1964, after a takeover of Mervyn’s by Gulton, Inc. had left the company severely depleted, Angus left Mervyn’s for Grubb-Parsons in the northeast of England to run their thin film activities. The company had built a superb reputation for building astronomical telescopes and was poised to expand into the production of scientific instruments and the manufacturing of thin film coatings. Ann and Angus had three small children under the age of 4, with another baby on the way, and somehow Angus found the time to immerse himself in work while also being a constant and loving presence at home. During his tenure at Grubb-Parsons, Angus was making not only multiple cavity narrowband filters for astronomical applications but also mirror coatings for gas lasers. The company enjoyed great success within the European market: Grubb-Parsons was the first company in Europe to produce a hard-oxide coating for a helium-neon laser rather than the previous porous coatings. Some way into Angus’ tenure, Grubb-Parsons was bought by Hilger and Watts, a scientific instrument company in the south of England. Noting Angus’s successes with filter production, Angus was approached by Neville Goodman of Adam Hilger, a scientific book publishing company owned by Hilger and Watts. Neville asked if Angus would be willing to write a book on optical filters. Angus explained that he could not cover the whole field of optical filters, but he felt he could handle a book on thin films, thus Thin Film Optical Filters was born. The first edition took two years to write and was completely typewritten by Angus on an old Remington typewriter. Published in 1969, it was a great success. The first edition went on to sell more than 4000 copies in English and more than 15000 copies were produced in Chinese.

By 1969 Grubb-Parson’s future was in doubt and Angus found himself at a crossroads. A readership position in thin film physics at Newcastle Upon Tyne Polytechnic (now Newcastle University) had become available and Angus decided to apply. He landed the post, thanks in part to the recent success of his newly published book, and he thus started down a path of academia. Angus thrived in this new environment: he thoroughly enjoyed teaching and also began his research career addressing all manner of problems he had experienced in the manufacture of infra-red narrowband filters. Oftentimes, it had seemed to him that monitoring systems did not behave as expected and he wanted to understand why. In a landmark paper published in 1972 [31] Angus used his admittance diagram to explain the now well-known compensation mechanism provided by optical monitoring. The admittance diagram, a graphical technique for understanding the behavior of an optical coating, was developed and introduced by Angus in the first edition of his book Thin Film Optical Filters.

This paper [31] attracted the attention of Emile Pelletier who was working at the University of Aix-Marseille on similar topics and was about to publish a paper in the same area. Emile reached out to Angus, and they decided to collaborate. A long and fruitful relationship ensued—both personal and academic. Angus and his family (Ann and Angus now had five children) spent multiple summers camping with Emile’s family in the south of France and Angus spent a very productive six-month sabbatical at Aix-Marseille as a Professeur Associé. Fluent in French, Angus taught thin-film optics classes with gusto and worked side by side with Emile in the lab. In 1997, in recognition of his contributions to the field of thin films, Aix-Marseille awarded Angus the degree of Doctor Honoris Causa.

In 1978 Angus received a phone call from Peter Franken asking if he would consider a professorship at the University of Arizona’s Optical Sciences Center. Angus and Professor Francis Turner of OSC had been communicating for some time, and this opportunity seemed too good to miss. In late October of ’78 Angus traveled to the U.S. for a tour of OSC and was asked by Franken to give a seminar with very little notice.

Angus’s research on production processes for narrowband filters led him to select a topic around the effects of moisture on optical coatings and the title he came up with (on the spot) was “A Bad Case of Rising Damp.” To Arizonans (and anyone who lives in a dry climate), this was not a familiar phenomenon and so it generated considerable (and to Angus, unexpected) interest. So much so that the entire first part of the talk had to explain what “rising damp” was (moisture that is wicked up the wall of an improperly protected building) before getting onto the real topic of moisture in coatings (which has a similar appearance). He was subsequently offered the position, and in 1979 he moved with his family to Tucson.

At OSC Angus’ research progressed: working on production methods to improve the stability of optical coatings. He had previously been able to make hard, dense films using the process of ion plating, but he was working on something simpler. Angus and his group powered forward with ion-assisted deposition, a process that was more straightforward to implement and control. As part of the effort in materials characterization, Angus collaborated on work to make Rutherford backscattering spectroscopy a useful tool for measuring the properties of thin films, enabling, for example, the measurement of a layer’s components and the degree to which argon had embedded in the layer, necessary for the optimization of the ion assist. Angus spoke frequently about how lucky he was to have his exceedingly brilliant students who came to OSC from all over the world. Angus’s family were also super-fortunate in that regard. Student get-togethers, game and quiz nights, dinners, and pool parties at the Macleod house were frequent events and strong bonds were forged all around. The students and OSC visitors were like family, and to this day the special relationships between Angus’s students and the Macleod family endure.

Shortly after his arrival at OSC, Angus developed a teaching program for the university mainframe computer. It was more successful than Angus anticipated, and it became obvious to Angus that computers could provide invaluable assistance to the thin film designer by effortlessly handling the volumes of calculations and tasks involved in the design process that are tedious, repetitive, and time consuming. In 1982 Angus was commissioned by a coating company to write a thin-film design program to run on a Radio Shack TRS-80 computer and when the Apple Macintosh computer appeared on the market in 1984 it marked a significant turning point. Angus soon had a thin film design program running on the Macintosh and found himself with offers to buy his software. Some sixteen years after transitioning from industry to academia, Angus began his transition back towards industry. Angus decided to split his time between research and lecturing at the university and developing thin film design software and providing training courses in thin film theory. With the first sale of his program for the Mac imminent, Angus and his wife Ann decided they were going to make a go of it and incorporated. Thin Film Center was born. In 1995, Angus retired from the University of Arizona and became full-time at Thin Film Center, but for many years he continued to teach his Optical Thin Films course for one semester each year. 1995 also marked the start of my full-time involvement with Thin Film Center. I had been working on the software part-time since late 1991, and Angus and I decided that I would need to relocate to the U.S. in order for us to optimize our joint efforts.

Angus loved to teach, and he saw the need for training courses, too. The most well-known of the TFC courses he presented was “Optical Coatings from Design through Manufacture.” This was a five-day course that was given both publicly and privately several times per year all over the world. In fact, he was presenting courses so often that he was actually teaching more hours at Thin Film Center than when he was a professor at the University of Arizona. In addition to courses provided by Thin Film Center, he also gave many, many short courses at various meetings, too. His focus in business was always to look after the customer. No question was too small (or large) to answer, and customer support was the thing he enjoyed most—right up until the end. Connecting with people was something he loved, and helping people was hugely rewarding for him.

Angus was recognized with multiple awards over the span of his extraordinary career. In 1987, he was awarded the SPIE Gold Medal for outstanding scientific achievements in the field of optical thin film technology. Ten years later, in 1997 he was awarded the Esther Hoffman Beller medal by the Optical Society of America (now Optica) for his contributions in education. In that same year, he received his Docteur Honoris Causa from the University of Aix-Marseille. In 2000, he received the John Matteucci Award at the International Conference on Vacuum Web Coating. The SVC in 2002 honored him with the Nathaniel H. Sugerman Memorial Award. The European Vacuum Coaters honored him, first in 2004 with the A Life For Thin Film Award and in 2008 with the Senator Award.

Angus served on many committees including the Optical Society of America (OSA) where he was on the board of directors from 1985 to 1987. He joined the executive council of the OSA in 1989, and he was also a member of and chair of the program for the Optical Interference Coatings conference. Subsequently he served on the OIC advisory committee, and he was a member of the OSA’s selection committee and its nominating council. He also served on the Society of Vacuum Coaters’ (SVC) board of directors and was President in 2008. He was conference chair for the first five SPIE Advances in Optical Thin Films conferences. He served on the program committee for the SPIE Nanostructured Thin Films conference for several years.

Angus’ bibliography is extensive. Over 300 publications bear his name. He has written broadly in the field of optical coatings. His evolving research interests began with the problems of producing narrowband filters with many papers published on optical monitoring. The discovery of the error compensation mechanism available with optical monitoring led work on moisture absorption and its impact on coating performance. In an effort to minimize moisture absorption, he looked at energetic processes for film deposition with considerable work on ion-assisted deposition. To understand the impact of using an ion gun to increase the density of a thin film layer, film microstructure was examined involving collaboration on developing techniques to make Rutherford Backscattering Spectroscopy applicable to the analysis of dielectric layers. In addition to his research papers, he also wrote many articles on the fundamentals of thin film design and the history of thin film optics. Many of these articles appeared in the SVC bulletin where he wrote articles several times per year over a period of 13 years.

On Thursday 29 April 2021, Angus passed away at his home in Tucson, Arizona, at the age of 87 years. Thin Film Center received hundreds of messages of condolence from customers and friends all over the world. We also received news of donations to charities and foundations in Angus’s honor—deeply meaningful gestures for which the entire family were grateful. In particular Clark Bright donated ${\rm {US}}\$50,000$ to the Society of Vacuum Coaters Foundation to establish a new annual scholarship called the Clark and Karen Bright Endowed Scholarship Honoring Angus Macleod, and in late September of 2021 we received news that VIAVI Solutions Inc. had established the H. Angus Macleod Scholarship at the University of Arizona Wyant College of Optical Sciences. I can think of no better way to honor the extraordinary contributions made by Angus to the field of thin film optics, and I will be forever grateful to Clark and to VIAVI for remembering Angus with such significant gifts.

I think Angus best summed up his legacy in the preface to Thin Film Optical Filters, Fifth Edition: