Dr. Charles H. Townes - PowerPoint Presentation

Slide1

Dr. Charles H. Townes

Tenure at Columbia University 1947-1961

Microwave Spectroscopy

Radiation Laboratory of Columbia University

As remembered by Fred M. Johnson PhD. Slide2

The Columbia University

RadiationLaboratory was situated on the 10th & 11thfloor of the Pupin Building. I remember one of the secretaries was Perl

Kipnis.

The

10

th

floor also had molecular

beam

experiments

, supervised by

Professors I.I

.

Rabi

and

P

.

KuschSlide3

During the tenure of Professor C.H. Townes

Physics Department Faculty Slide4

Faculty ContinuedSlide5
Slide6
Slide7
Slide8
Slide9

Physics Students of Townes who did not complete PhD program

Mirek Stevenson

(later IBM

)

Joe A. Klein

PhD. Students ContinuedSlide10

Radiation Lab Employees

Glass Blower – Deery ( each student who was about to get his PhD got a long-stem wine glass with teardrop inside the stem!) That was an early signal that one was about to graduate with a PhD. How did he know? I still have this wine glass.Machine Shop –about 7 employeesChemist – Dr. Gene SilveyElectronic Shop

(with

student

assistants)

240 V power supply with outside case being at 240V !! Was almost fatal when I discovered it: Right hand on (hot) metal switch, while having my left hand grounded.

Microwave equipment Laboratory ( Led by Ned Nethercott ): I met Arno Penzias working there

.

Magnetrons were still being produced in the Radiation Laboratory on a regular basis, following a WW II

tradition.

Supported by the Office Of Naval Research Lab, Department of Army

and Air

Research Development

Quarterly reports were published (included a summary of publications during each ¼ ). It was my assignment to produce this page.

An

important contributor from the Chemistry department was Dr. B. P. DaileySlide11

Professor Townes was hired as an associate professor of Physics at Columbia in 1948 (by I.I. Rabi

). CHT became a full professor in 1950, Director of the Columbia Radiation Lab 1950-1952, and was Chair of the Physics Department from 1952 to 1955.

Townes

took his sabbatical 1954-1955. During his sabbatical he visited Japan, in Israel he met with Willi Low, in France with A. Honig. He probably also met with other colleagues and former students. On his return, he worked out the line width problem associated with anti-ferromagnetic resonance research, (on a blackboard in his office). It is acknowledged in my thesis

.Slide12

The Radiation Laboratory became the perfect place for research

relating to unique physical properties and structures of specific molecules. The microwave equipment included klystrons and magnetrons from WW II plus associated left-over waveguides and even submarine batteries. The STARK effect and heterodyning methods were employed to investigate a whole range of molecules which were produced either by the in-house chemist or by a colleague from the Chemistry department. Slide13

Some of these chemicals were highly toxic, such as HCN (a bird in a cage was used as a warning signal in case of vapor leakages). The electronic signal detection technique required modulation of the pulsed STARK electric field and the use of Lock-in detection to increase the signal to noise ratio. A host of successive graduate students were assigned specific molecules for their PhD thesis.Slide14

Topics included:

Spin and Quadrupole Moments of nuclei, Nuclear Magnetic moments, STARK Effects, Hyperfine Structure and Exchange Narrowing of Paramagnetic Resonance as well as Polarization of the Nucleus by Electric Fields.Higher microwave frequencies were sometimes needed. Thus, magnetron harmonics produced the desired millimeter wavelengths. This required a lot of patience and experience. It was one of the special skills of Ned Nethercot.Slide15

It was the need for these higher frequencies that motivated Prof. Townes to search for new techniques to generate frequencies in the millimeter and sub-millimeter region. As early as 1951, he had discussed this with Nethercot and suggested something along the lines of stimulated emissions from excited atomic levels. The big problem was to overcome the Equilibrium Boltzmann Temperature effect in the distribution of energy states. Townes was clearly aware of Einstein’s stimulated emission theory. The problem was how does one achieve population inversion?Slide16

His sabbatical year, I believe, was used effectively in this direction; however he already had assigned Jim Gordon and Herb Zeiger, a post-grad student from Rabi’s lab, who was experienced with molecular beams, to work on the Maser project. Thus the first demonstration of stimulated emission used an enhanced upper state of ammonia to enter a microwave cavity: Maser demonstration occurred in 1954, the rest is History. Townes confided to me later on when we met at Berkley recently, that both Rabi and Kusch had strongly opposed his use of funds for this experiment. Townes said he was glad he had tenure in the Physics department.Slide17

Ali Javan and I took his atomic physics class in the fall of 1949. Ali was my best friend. I stood next to him when he introduced himself to Townes, mentioning the name of a French Professor, as a reference.

I was accepted by Townes as his graduate student in 1952 and assigned to study microwave absorption in solid crystals at low temperatures, including magnetic fields. I inherited some of the equipment that was used by Willis Lamb in his classic Lamb Shift experiment. New equipment had to be designed and built (essentially “from the ground up”). Slide18

Some of my engineering background greatly helped with this project. It required RG 99 size wave guides for millimeter waves to be introduced into a liquid helium Dewar. There was a special design feature which facilitated a small crystal to be subjected to millimeter microwave radiation and allowed it to rotate. The main hurdle was to produce millimeter waves from still functioning old magnetrons from WW II. Slide19

The harmonic generation required cat’s whisker tungsten wire

(sharpened by electrolysis) in contact with a silicon wafer in order to produce the non-linear effects. This was a major challenge; I also had to grow Tutton salt single crystals, these proved to be similar to the crystals that I.I. Rabi used in his PhD thesis. Slide20

I discovered Rabi had made a mistake with his crystals in the 1920’s, which so far no one had discovered or talked about, it was a simple error of a crystal mix-up. (I kept this secret to myself…until now) Later (about 1955-1956) we switched to MnF2 single crystals (gifts from Prof. Stout, via Nethercott). Thus began the work on anti-ferromagnetic resonance research. The results of this subsequent research (which morphed into a PhD thesis) can be found in Kittel’s Solid State text book.Slide21

I was a teaching assistant from 1951 to 1954 in the Astronomy Department of Columbia University. I took all the Astronomy graduate courses that were offered. My teacher and mentor was Prof. Lloyd Motz. In 1953, Rupert Wildt, a visitor from the Yale Astronomy department, suggested a possible solution to the enigmatic identity of a few diffuse interstellar bands. Even though I proved his suggestion experimentally wrong, it alerted me to this astronomical mystery.Slide22

Wildt suggested that I perform spectroscopy on F-centers in alkali hydrides. I accepted the challenge with the permissions from Professor Townes, who stated (in writing) that if I solved the problem I would get a PhD on that topic.

A strenuous year followed (1953-1954) of working on this problem, including taking spectra of F-centers at liquid helium temperatures. This was clearly not the correct solution.Slide23

I resumed my previous assignment dealing with millimeter wave spectroscopy. (Professor Kusch called me into his office and suggested that this difficult astronomy problem

would better be solved after I obtained my PhD in Physics. 60 years have passed since then. I believe, I have finally cracked this elusive code, which solved this problem.Slide24

Townes’ work schedule: about 9am- 10:30pm, 6 days a week including holidays: special talent: glass blowing, Languages: German, French and Russian.

My work assignment as of 1954: 20 hrs/week calculating (Friden calculator) Salary: $200/month. I had to drop astronomy teaching at $100/mo. Townes gave me the option. The combined salary would have made me too rich!Slide25

Future research - Biology or Astronomy

Townes’ DilemmaCHT (1951-1955) prepared a list of molecules that might be in the interstellar medium. (list was published 1957). OH was of prime interest, studied by George Dousmanis in the lab and later discovered by Alan Barrett in outer space. Included CO, CS, H

2

O, HCN, NH

3

…

CHT (1955) on return from Sabbatical: He provided me with a stack of Astronomical reprints, including

latest

findings about the CRAB Nebula: Its acceleration during its expansion – I wrote up a paper with CHT as co-author.Slide26

ANECDOTES

What were the characteristics that made C.H. Townes so successful?Knowledge, enormous energy, drive, focus, creativity, excellent health and his wife Frances.LUCK vs. HARD WORK. CHT did not believe in luck, yet, in his book “How the laser happened”, p.31 he writes: “

Pay close attention to HAPPENSTANCE”

(= luck??).

Lunch every Friday at a Chinese Restaurant on Amsterdam Ave. with most of his students. I did not join them. However, once I took CHT with me to a dairy meal at the Theological Seminary on 122 St and Broadway.

The number of daughters by each of the Physics Dept chairs (in arithmetic progression): I.I. Rabi 2; P. Kusch 3; C.H. Townes 4.

Townes had done some research on how to enhance the probability of getting a son. (As was talked about and shared with me by Ned Nethercott).Slide27