a laser pioneer... ... THEODORE H. MAIMAN

THE FIRST LASER

Based on the book : LASER PIONEER INTERVIEWS
A Laser & Applications Publications High Tech Publications Inc Torrance , California
@ 1985 printed in 1.960 to celebrate the 25th anniversary of the laser ...

The background ...

Ted Maiman´s career has always been marked by more than a bit of iconoclasm . While theoretical physicists wrote papers and debated the merits of different materials and approaches for a laser , Maiman set out to build one .

A pragmatic scientist , one of his main concerns was practicality - he not only wanted to build a laser , but he wanted the device to be easy to work with . Along the way , Maiman had to overcome obstacles put in place by scientific colleagues , supervisors ... and the laws of physics . He was determinated , however , to let nothing stand in his way . It was his independent attitude that helped Maiman to win the race to build the first laser . In May , 1960 , he demonstrated laser action from a ruby crystal while working at Hughes Research Laboratories in Malibu , California .

Maiman received graduates degrees in both engineering and physics from Stanford University , where he studied under Nobel Prize winner Willis Lamb . He is a fellow of both the American Physical Society and the Optical Society of America , a member of both the National Academy of Science and the National Academy of Engineers , and a recent inductee to the National Inventor´s Hall of Fame .

Maiman left Hughes in 1962 to found Korad Corp , one of the first manufacturers of laser equipment . From 1976 to 1983 he was vice-president of advanced technology for TRW Inc´s electronic and defense sector . He is currently a consultant in Marina Del Rey , and a director of PlesCor Optronics .

The great Laser Race ... and the ruby laser works ... by Jeff Hecht

Meanwhile , Theodore Maiman was trying to use his knowledge of ruby masers to make a laser at Hughes Research Laboratories in Malibu. As he relates , he forget ahead , working alone , despite assurances by Schawlow and others that ruby was unsuitable for a laser . Maiman knew better , but those statements led to frowns by management . By the time he succeeded in making the ruby laser work for the first time , on May 16 , 1960 , he was not supposed to be working on the program.

Maiman´s success is undisputed , but almost immediately he ran into problems in reporting that success . Hughes´ management reacted enthusiastically once the laser worked and sponsored a full-fledged press announcement in early July . However , the public relations photographer commissioned to immortalize the first laser on film wasn´t satisfied with it . He thought the device too small and insisted that Maiman pose with a bigger flashlamp and ruby road . Today Hughes is still distributing those pictures , showing Maiman with what isn´t really the first ruby laser .

A more serious problem came when Maiman submitted his paper for publication . The then-new Physical Review Letters summarily rejected it as " just another maser paper " . The journal´s founding editor , Samuel Goudsmit , a theoretician best known as the codiscoverer of electron spin , had grown tired of the glut of maser papers arriving at his office , and decided they no longer merited rapid publication . Maiman hurriedly prepared a concise 300-word report which was immediately accepted by the British weekly Nature , and when efforts to convince Goudsmit of his error failed , Nature carried the first report of the laser on August 6 , 1960
Theodore H. Maiman " Stimulated optical radiation in ruby " Nature Vol 187 p. 493 ( Aug. 6 , 1960 )

Maiman later published a more detailed analysis in Physical Review
Theodore H. Maiman " Stimulated optical emission in fluorescent solids , Part 1 , Theoretical considerations " Physical Review Vol. 125 p. 1145 ( 1961 ) ;
Theodore H. Maiman , R.H. Hoskins , I.J. D´Haenens , C.K. Asawa , and V. Evtuhov , Part II , Physical Review Vol 125 p. 1151 ( 1961 )

Schawlow´s group at Bell Labs was among the first to get one duplicated working , and soon afterwards they and another group reported laser action on slightly different lines in " dark " or " red " ruby , which has a higher concentration of chromium ions than the " pink " ruby Maiman used .

Duplication of Maiman´s " pink " ruby laser ( with low chromium ion concentration ) was reported in
R.J.Collins , D.F. Nelson , A.L. Schawlow , W. Bond , C.G.B. Garret , and W. Kaiser " Coherence , narrowing , directionality , and relaxation oscillations in the light emission from ruby " Physical Review Letters Vol 5 p. 305 ( 1960 )

Production of emission on different lines in " red " ruby with higher chromium concentration was reported in
A.L. Schawlow and G.E. Devlin " Simultaneous optical maser action in 2 ruby satellite lines " Physical Review Letters Vol 6 p. 96 ( 1961 )
I. Weider and L.R. Sarles Physical Review Letters Vol 6 p. 95 ( 1961 )

How did you first get involved in Laser Research ?
One of the questions of Jim Cavuoto to Theodore H. Maiman in the interview conducted on Novemver 14 , 1984 , in Marina Del Rey , California
LASER PIONEER INTERVIEWS , A Laser & Applications Publications , High Tech Publications Inc , Torrance , California @ 1985

Answer :

I did some microwave optical experiments during my PhD work at Stanford , where I was looking into the fine structure of the excited states of Helium . I devised a measurement technique to analyze optical structure using a combination of electronics , microwaves and optical instrumentation . The process used a parallel plate resonator coupled to a low-pressure helium discharge .

Later , I went to work for Hughes Research Labs in the newly-formed Atomic Physics Department . The real charter and interest of the department was to generate higher coherent frecuencies than were currently available . This was about the time that the ammonia maser came out . Hughes had an intense interest in maser research at that time . But at first , I worked on a contract I brought in which used a nonlinear aspect of cyclotron resonance to generate harmonics .

... Was your commitment to ruby as a laser material at all influenced by the success you had with it in your maser work ?

No , not at all . I didn´t know what material I was going to use at first , but I was thinking that I wanted it to be something fairly rugged . After my experience with the maser , I did not want anything that had to be cooled cryogenically .

I used ruby just as a starting point . I constructed an analytical model and made some detailed calculations . I could see that it would be very difficult to make it work . Further , Weider had published a paper which indicated that the quantum efficiency of ruby was maybe 1 % . If that was true , it would rule out ruby for sure . I looked at some other materials , like gadolinium-doped crystals , because they displayed some very sharp lines . But the problem is that not only is the fluorescence very sharp , the pumping bands also . In adition , it´s in the ultraviolet , and it´s hard to get much pumping energy . I went back to ruby , not only to try to work on it as a laser , but again as a model , because I liked some of the other propierties .

Were you suspicious of the calculation on the quantum efficiency of ruby at this point ?

No I wasn´t . In fact , quite the contrary . I decided to use ruby because it had other propierties that were interesting . It has a simple energy level scheme , was rugged , and in principle I wouldn´t have to cool it below room temperature. To make it work , it wouldn´t have to be very big - you didn´t need a 1-meter cavity , as the discharge people were proposing . I decided to find out what was wrong with ruby , and then , working with some materials experts , use that as a clue to find another material that would have similar properties with the desirable qualities , but without the bottleneck - the low quantum efficiency .

I made some detailed measurements to find out where the bottleneck was , and I devised a model to show what was going on . As I went through the model and looked through all the possible problem areas , I couldn´t find the problem . In fact , I found the quantum efficiency was fairly high , about 75 % . So , armed with that , I started to think more seriously about ruby ...

I started to get a little more interested in ruby when I found the quantum efficiency was near unity . I knew it would still take a lot of power , though . Also , I wasn´t going to dismiss the supposed problem of having depopulate ruby ´s ground state without studying it in some detail to see what was really involved .So I went through the calculations and came across the fact that for such a system what was really important was the brightness of the pumping source - which amounted to the equivalent of a black body of some 5.000 K . This was not unheard of , but it was really pushing the specifications of the common laboratory lamp .

I first analyzed a design with a straight mercury lamp and a ruby rod in an elliptical cylinder and concluded that operation might be possible , but very marginal ( Incidentally , several years later Evtuhov at Hughes did make such a cw ruby laser ) .

I image practical problems like that played a very important role in the developement of the first laser...

Absolutelly . My calculations told me the laser would work , at least marginally . But that wasn´t good enough . I decided that , if I had to go all the trouble of putting the experiment together , it would have to work . With the margin that close , I was very worried that the laser wouldn´t quite lase . What if I was just below threshold ? That would have been very frustrating .

My insight regarding the high lamp temperature proved to be very important . I remember reading that the effective temperature of a xenon flashlamp was 8.000 K . Also , I didn´t see any reason why I had to do this continuouswave - pulsed mode was perfectly fine ... Another consideration that kept me hanging in with ruby was that , if it worked at all , it would be small and compact and operate at room temperature . I was also intrigued by the fact that , if it worked , ruby would emit visible light . I would be able to see it ... I decided to think more about the xenon lamp .

I went through the catalogs of available laboratory lamps , and calculated the effective brightness rather than being concerned with the size or the joules delivered , because my calculations showed that , within reason , the size of the ruby would not be important . And as I screened them and isolated them , there where only three lamps that had enough brightness to do it . All three of them were made by General Electric and all three of them where quartz helices . I bought a few versions of all three : FT503 , FT506 and FT624 ( a monster , designed for aerial photography ) . They all had enough brightness . So my first laser used the smallest , a GE FT506 lamp . The ruby was about 1 centimeter in diameter by 2 cm long , just filling the lamp spiral .

That brings up a humorous anecdote . When the Hughes public relations people took the photographs of my first laser , they used the FT503 flashlamp because it was more photogenic . So when the press release got circulated , everybody thought that was the lamp I used . There was a run on those lamps . All of the reproductions of the ruby laser made in other labs used the FT503 ...

... How did you come to place the ruby crystal inside the flashlamp ?

The spiral lamps were the ones that had those high brightness temperatures at that time . High brightness straight lamps weren´t available , so I couldn´t use my elliptical cylinder design for a continuous wave laser . Because their odd shape the helical lamps weren´t very amenable to reflectors . In fact , I started to try to devise a focusing reflector to direct the light onto the ruby . I was talking to a distributor of GE lamps , and he told me that the big one , the FT624 , was so intense that it would set a piece of steel wool on fire . Then all of a sudden it clicked in my head . Of course ! The best I could do if I put that lamp in a reflector and then collected and refocussed it back on the ruby was the brightness of the lamp itself. I though , " Instead of remotely transferring the brightness of the lamp to the ruby , why don´t I put it in near proximity ? " I´d still be at the same brightness . I put a reflector around the outside of the lamp to collect the radiation that would travel outward . It acts as a radiation shield and , in principle , increases the brightness of the lamp for the same input power . There´s the design .

And of course it came out extremely simple in realization . As with the maser , I painted the cavity right on the ruby - in fact silver again , only it wasn´t paint . I evaporated silver onto the endfaces . Multilayers were around , but they were in early developement ... That´s when I got the idea , again relating back to the microwave era , that since it was a cavity , I´ll just put ain a coupling hole . So I put full silver on each end and then bored a tiny coupling hole to observe what was going on . Later I plotted the output versus the hole size and found the optimum hole size . That was the progression.

... It seems from your experience that there was a large disparity between the paper world of the scientific literature and the practical world of the laboratory . But were you at all influenced at the time by what was being published in the literature ?

Well , I saw the proposals and I though , " Fine , go to it , have fun , because you have a lot of problems there " ...

... Did you find yourself getting caught up in a race with other research teams to build the first laser ?

I would say that I made the commitment around August , 1959 , to work on laser . I knew there was a lot of interest . I knew what people were doing , but I felt they were going off in tough directions . Schawlow and Townes must have started their work in the spring of 1958 . There it was August , 1959 , and I was aware of the fact that people all over the world were now in this race . It was a little brash for me to enter that race at that time . People with well-funded efforts had already been doing for , let´s say , a year . It´s interesting to note that Hughes´ total expenditures in our nine-month laser effort amounted to about $50.000 ... Contrast that with the $500.000 to $1 million that other research teams were spending ...