Transcript Slide 1
From basic science to technology: a brief journey though some of the greatest achievements of human genius
“Love is a better teacher than a sense of duty” A. Einstein
Francesco Piazza,
Physics Department, University of Orléans
Gustav Kirchhoff , 1824-1887 Sony, 1976 Philips 1979
Gustav Kirchhoff , 1824-1887
The black body
Tiny hole in insulated enclosure The idea of a black body originally was introduced by Gustav Kirchhoff in 1860 as follows:
...the supposition that bodies can be imagined which, for infinitely small thicknesses, completely absorb all incident rays, and neither reflect nor transmit any. I shall call such bodies perfectly black, or, more briefly, black bodies.
The ultraviolet catastrophe and the birth of Quantum Mechanics
The Ultraviolet catastrophe is the error at short wavelengths in the Rayleigh–Jeans for the energy emitted by an ideal black-body. law Lord Rayleigh, 1900 Sir Jeans 1905
Max Planck, 1858-1947
Energy comes in quanta!
Max Planck who in 1900 proposed the relationship between the frequency of radiation and energy and, for the first time suggested that energy could be emitted only in
discrete chunks.
Albert Einstein, 1879-1955
Stimulated emission, 1916
Einstein, A (1916) Strahlungs-emission und -absorption nach der Quantentheorie. Verhandlungen der Deutschen Physikalischen Gesellschaft 18: 318–323.
(Radiation emission and absorption in quantum theory)
Rudolf Ladenburg, 1882-1952
1928
Hans Kopfermann, 1895-1963
H. Kopfermann and R. Ladenburg Experimental Proof of ‘Negative Dispersion’, Nature Volume 122, 438-439 (22 September 1928)
Negative dispersion is stimulated absorption!
Valentin A. Fabrikant, 1907
in 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify “short” waves. His thesis for a professorship “The emission mechanism of a gas discharge“ was defended in 1939 at P.N.Lebedev Institute, and in 1940 was published. It contained a section on “Experimental evidence for the existence of negative absorption” which was not included in the publication, but has later been published with an English translation.
Willis Lamb, 1913-2008
in 1947, Willis E. Lamb (Nobel in Physics 1955) and R. C. Retherford found apparent stimulated emission in hydrogen spectra and performed the first demonstration of stimulated emission
They were working to measure the energy difference between two excited levels of the hydrogen atom, which should have had the same energy according to Dirac.
Stimulated emission alone does not make a laser though …
Alfred Kastler, 1902-1984
He researched quantum mechanics, the interaction between light and atoms, and spectroscopy. Kastler, working on combination of optical resonance and magnetic resonance, developed the technique of
"optical pumping”
(1952).
Optical pumping is a process in which light is used to raise (or "pump") electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction, to pump the active laser medium so as to achieve population inversion.
A. Kastler won the Nobel Prize in Physics in 1966
The micro-wave way
1938-1945 World troubles. The rise of radar and molecular physics
Starting in 1934 engineers were interested more and more in microwaves, which assumed great relevance a few years before and during the Second World War with the construction of the radar.
After World War II, radar scientists looking for ways to generate electromagnetic radiation at wavelengths shorter than one
centimeter began collaborating with physicists who wanted to use such radiation to investigate molecular structure
. When atomic bonds inside a molecule flip between slightly different forms, they often absorb or emit centimeter- or millimeter-band radiation.
Charles Townes, 1915 -
Nobel prize in physics, 1964 Charles Townes, then at Columbia University in New York City, had the idea that
molecules themselves would make good emitters of the desired wavelengths
, if only he could persuade large numbers of molecules to emit en masse.
Townes was familiar with microwave engineering techniques. If he could assemble a population of excited molecules in a cavity with the right dimensions, radiation emitted by some of the molecules would reflect back and interact with other molecules, causing further stimulated emission.
The feedback loop between the cavity and molecules would dramatically amplify the signal
, he reasoned…
The Microwave Amplification by Stimulated Emission of Radiation (MASER)
J.P.Gordon, H.J.Zeiger, C.H.Townes, Phys.Rev. 95, 282 (1954) Townes and his colleagues built the first maser in 1954. They sent a beam of excited ammonia molecules into a resonant cavity. Emission became self-sustaining as radiation from molecules in the cavity stimulated further radiation from the continuously renewed supply of excited molecules.
The energy was concentrated in a spectacularly sharp line in the emission spectrum
The Russian MASER:
operating continuously!
Alexander Prokhorov, 1916-2002 At variance with what occurred in America, neither Basov nor Prokhorov were familiar with the radar, nor had worked on it. They arrived to the maser concept by the spectroscopy side and
the generic wish to create new kinds of sources in the centimeter wavelength range.
Prokhorov and Basov were interested in spectroscopy with molecular beams and to increase sensitivity decided to artificially vary the population on the levels. The transmission of a beam of molecules in the upper state through a resonator so that the field generated by the beam reacts on the beam provoking an oscillation, was described by them theoretically at a Soviet conference on radio spectroscopy in may 1952. At this conference they discussed the possibility to excite CsF molecules. In the discussions that followed ammonia was suggested too.
Nikolay Basov 1922-2001
The 1964 Nobel prize in Physics
Townes reports that several eminent physicists — among them Niels Bohr, John von Neumann, Isidor Rabi, Polykarp Kusch, and Llewellyn Thomas — argued the maser violated Heisenberg's uncertainty principle and hence could not work!
The 1958 paper by Schawlow and Townes. The race is on!
Physicists everywhere realized that an "optical maser" could be built. Teams at half a dozen laboratories set out, each hoping to be the first to succeed… Arthur Schawlow 1921-1999 1981 Nobel Prize in Physics
1960: the birth of LASER
Hughes Research Laboratories, Malibu Theodore Maiman, 1927-2007 T. Maiman, “Stimulated Optical Radiation in Ruby,” Nature (London) 187, 493 (1960).
Hughes Research Laboratories Maiman realized that
a flash lamp could do the pumping …
1. High-voltage electricity causes the quartz flash tube to emit an intense burst of light, exciting some of the atoms in the ruby crystal to higher energy levels.
2. At a specific energy level, some atoms emit particles of light called photons. At first the photons are emitted in all directions. Photons from one atom stimulate emission of photons from other atoms and the light intensity is rapidly amplified.
3. Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification.
4. The photons leave through the partially silvered mirror at one end. This is laser light.
Although many different types of lasers have been invented since Maiman's device, the ruby laser is still used, mainly as a light source for medical and cosmetic procedures, and also in high speed photography and pulsed holography.
Gustav Kirchhoff , 1824-1887
1860-1960 From the black body to the laser!
Sony, 1976 Philips 1979
1905: the annus mirabilis
On November 21 Annalen der Physik published a fourth paper "Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?” "Does the Inertia of a Body Depend Upon Its Energy Content?” in which Einstein developed an argument for arguably the most famous equation in the field of physics
This equation shows that a massive particle possesses an energy, the rest energy, distinct from its classical kinetic and potential energies.
If a body gives off the energy L in the form of radiation, its mass diminishes by L/c 2 . The fact that the energy withdrawn from the body becomes energy of radiation evidently makes no difference, so that we are led to the more general conclusion that the mass of a body is a measure of its energy-content.
An impressive potential hidden in this simple formula: the history of nuclear fission
In 1923, while writing the appendix for the Italian edition of the book “The Mathematical Theory of Relativity” by A. Kopff, Enrico Fermi pointed out, for the first time, that hidden inside the famous Einstein equation,
there was an enormous amount of nuclear potential energy to be exploited… Another 15 years should elapse though …
Enrico Fermi 1901-1954
Radioactivity
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles or ionizing radiation. There are many different types of radioactive decay. In some decays the parent and daughter are different chemical elements, and thus the decay process results in nuclear transmutation (creation of an atom of a new element).
The first decay processes to be discovered were alpha decay, beta decay, and gamma decay.
Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials… He discovered a strange radiation coming from Uranium salts that had nothing to do with Phosphorescence… Antoine Henri Becquerel, 1852 – 1908 As often happens in science, radioactivity came close to being discovered nearly four decades earlier when, in 1857, Abel Niepce de Saint-Victor, who was investigating photography, observed that uranium salts emitted radiation able to darken photographic emulsions: ”…a radiation that is invisible to our eyes" Claude Félix Abel Niépce de Saint-Victor, 1805 1870
Rutherford discovered the concept of radioactive half-life, proved that
radioactivity involved the transmutation of one chemical element to another
, and also differentiated and named alpha and beta radiation.
He got the 1908 Nobel prize in Chemistry She formulated a theory of radioactivity (a term that she coined), techniques for isolating radioactive isotopes, and the discovery of polonium and radium. Ernest Rutherford, 1871 – 1937 She also conducted the first studies for the treatment of neoplasms using radioactive isotopes. Maria Skłodowska-Curie, 1867 - 1934 1903 Nobel prize in Physics 1911 Nobel prize in Chemistry Pierre Curie, 1859 – 1906
Fermi does obtain fission of Uranium in 1934 … but does not realize it!
After English physicist James Chadwick discovered the neutron in 1932, Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons in 1934. Fermi concluded that
dubbed Hesperium his experiments had created a new element with 94 protons, which he
. However, not all were convinced with Fermi's analysis of his results. The German chemist Ida Noddack notably suggested in 1934 that instead of creating a new, heavier element, that "it is conceivable that the nucleus breaks up into several large fragments." Enrico Fermi 1901-1954 At that time, fission was thought to be improbable if not impossible, mostly on theoretical grounds
Nobody expected neutrons to have enough energy to actually split a heavier atom into two light element fragments …
The first demonstration of nuclear fission: 1938
After the Fermi publication, Otto Hahn, Lise Meitner, and Fritz Strassmann began performing similar experiments in Berlin.
Fritz Strassmann, 1902-1980 While in Sweden, Meitner received a letter from Hahn describing his
chemical proof that some of the product of the bombardment of
uranium with neutrons was barium. Hahn was unsure of what the physical basis for the results were— barium had an atomic mass 40% less than uranium… Otto Hahn, 1879-1968 Lise Meitner, 1878-1968
Was it a mistake? No, said Lise Meitner; Hahn was too good a chemist for that. But how could barium be formed from uranium? After separation, the two fragments would be driven apart by their mutual electric repulsion and would acquire a very large energy, about 200 MeV
where could that energy come from? .
Lise Meitner... worked out that the two nuclei formed by the division of a uranium nucleus together would be lighter than the original uranium nucleus by about one-fifth the mass of a proton.
Now whenever mass disappears energy is created, according to Einstein's formula E=mc 2
, and one-fifth of a proton mass was just equivalent to 200MeV. So here was the source for that energy: it all fitted!
The binding energy per nucleon increases in the fission products
Fission
The chain reaction and the birth of nuclear energy
"Chain reactions” were a known phenomenon in chemistry, but the analogous process in nuclear physics, using neutrons, had been foreseen as early as 1933 by Szilárd, although Szilárd at that time had no idea with what materials the process might be initiated.
Szilárd considered that neutrons would be ideal for such a situation, since they lacked an electrostatic charge.
Leó Szilárd, 1898 – 1964 With the news of fission neutrons from uranium fission, Szilárd immediately understood the possibility of a nuclear chain reaction using uranium.
Fermi and Szilard proposed the idea of a nuclear reactor (pile) to mediate this process. The pile would use natural uranium as fuel. The famous Chicago PILE-1.
The Chicago Pile 1
The birth of the modern nuclear era: the Einstein letter to president Roosevelt
In August 1939, Szilard and fellow Hungarian refugees physicists Teller and Wigner thought that the Germans might make use of the fission chain reaction They persuaded German-Jewish refugee Albert Einstein to lend his name to a letter directed to President Franklin Roosevelt.
The Einstein–Szilárd letter suggested the possibility of a uranium bomb.
The President received the letter on 11 October 1939 — shortly after World War II began in Europe, but two years before U.S. entry into it. Roosevelt ordered that a scientific committee be authorized for overseeing uranium work and allocated a small sum of money for pile research.
This marked the official birth of the Manhattan project… the nuclear era had begun
1916
Electricity was generated by a nuclear reactor for the first time ever on December 20, 1951 at the EBR-I experimental station near Arco, Idaho in the United States.