Category: optics

Since the 16th century CE, improving the limits of optical resolution has become an essential technical goal in optics research, and it continues to challenge us even today. When they were introduced, optical microscopes opened a new world for humans to observe, learn and eventually control matter at microscopic scales. A logical progression in this thought was to extend the resolution limit to the atomic scales unavailable to optical microscopes. Enter the ‘electron’ microscope. They changed the game entirely and paved the way to visualize matter at the atomic scale.

Electron microscopes were invented in the 1930s. When they were built in some laboratories, there was considerable public interest in understanding these “advanced” tools, as witnessed by a short but interesting article in the September 1940 edition of Popular Mechanics.

Sept 1940: Above is an image and description of one of the earliest electron microscopes published in Popular Mechanics

Reference: Popular Mechanics ~ 1940. n.d. Accessed January 7, 2024. http://archive.org/details/PopularMechanics1940.

The article speculates

First applications of the electron microscope are expected to be in biological and industrial research.

This is interesting because electron microscopes were still in their infancy, and the working principles were explored for better quality images and sample durability.

The origins of the electron microscope have an interesting history and were inspired by optics (for an interesting commentary, see Freundlich, Martin M. 1963. “Origin of the Electron Microscope.” Science 142 (3589): 185–88. https://www.jstor.org/stable/1712183). The first demonstration of a working microscope was by Ruska and Knoll (Z. Tech. Phys., 12 (1931)), and the conceptual foundations date back to the late 1890s. Ruska was eventually awarded a Nobel prize for his work on electron optics and the invention of the electron microscope in 1986.

As with any development in science and technology, an idea becomes a seed to another idea. In the case of electron microscopy, it led to some early motivations behind the invention of optical holography by Dennis Gabor, which eventually fetched him a Nobel Prize in 1970.

Dennis Gabor was also inspired and interested by the invention of electron microscopes. He played a critical role in formulating the problem of resolution limit, which further led to the invention of holography. To quote his Nobel lecture :

Let us now jump a century and a half, to 1947. At that time I was very
interested in electron microscopy. This wonderful instrument had at that time
produced a hundredfold improvement on the resolving power of the best light
microscopes, and yet it was disappointing, because it had stopped short of resolving atomic lattices. The de Broglie wavelength of fast electrons, about
l/20 Ångström, was short enough, but the optics was imperfect. The best
electron objective which one can make can be compared in optical perfection
to a raindrop than to a microscope objective, and through the theoretical
work of O. Scherzer it was known that it could never be perfected.

Interestingly, Gabor started his work in Germany but had to move out of the country due to the political situation. As he mentions in his biographical note :

In 1933, when Hitler came to power, I left Germany and after a short period in Hungary went to England. At that time, in 1934, England was still in the depths of the depression, and jobs for foreigners were very difficult. I obtained employment with the British Thomson-Houston Co., Rugby, on an inventor’s agreement. The invention was a gas discharge tube with a positive characteristic, which could be operated on the mains.

He stayed back in England and continued his work. The important aspect is that the development of electron microscopy eventually led to some fundamental experiments in optical holography. To quote Gabor’s biographical note :

The years after the war were the most fruitful. I wrote, among many others, my first papers on communication theory, I developed a system of stereoscopic cinematography, and in the last year, 1948 I carried out the basic experiments in holography, at that time called “wavefront reconstruction”. This again was an exercise in serendipity. The original objective was an improved electron microscope, capable of resolving atomic lattices and seeing single atoms. Three year’s work, 1950-53, carried out in collaboration with the AEI Research Laboratory in Aldermaston, led to some respectable results, but still far from the goal. We had started 20 years too early. 

The general notion in optics is that experiments in the visible light frequencies led to developments in electron microscopy. In the case of optical holography, at least in the initial stages of its invention, electron microscopy played a critical role. Developments in electron optics led to some fundamental questions in optical wavefront reconstruction. This further led to optical holography.

This reminds me of a quote attributed to Buckminster :

How often I found where I should be going only by setting out for somewhere else.