Nikolai Borisovich Delone, a scientist famous in Russia and well-known world-wide, one of the pioneers and creators of atomic and molecular multiphoton physics, died in Moscow, Russia, on September 11, 2008, after a vast cerebral stroke. This is a great loss to atomic, molecular and laser science, to all friends, former and present students, and to his family.
Nikolai Delone was born in Leningrad (now St.-Petersburg, Russia) on May 22, 1926, in the family of another well known scientist, mathematician Boris Nikolaevich Delone. Nikolai Delone graduated from the Moscow Engineering Physical Institute and joined the P.N. Lebedev Physics Institute in 1951. His PhD work was in the field of nuclear physics and bubble chamber physics. After the appearance in 1964 of the seminal theoretical paper by L.V. Keldysh on strong-field ionization of atoms, N.B. Delone published the first paper on experimental observation of multiphoton ionization in 1965. This pioneering work had the strongest impact on the further development of physics of laser-atom interactions throughout the world.
The next notable discovery by Prof. Delone was made in 1979 together with scientists from Uzhgorod, USSR (now Ukraine). This was the first experimental observation of two-electron ionization of atoms in a laser field. One of us (MVF) reported this important result on behalf of Delone, in one of the early international conferences on multiphoton processes in Benodet, France, in 1979. At that time Delone could not get permission from the Soviet authorities for going abroad. As soon as the first results obtained by Delone and his colleagues on two-electron ionization became known to the scientific community, intensive work was carried out first in the University of Bielefeld in Germany (Karl Welge, with the collaboration of one of us, SLC) and then in the Saclay group (Gerard Mainfray). Ionization of two or more electrons has remained a hot topic to the present day.
In 1986 Prof. Delone, with M.V. Ammosov and one of us (VPK), suggested the so-called ADK formula for tunneling ionization of atoms in a laser field after receiving the first experimental results on tunneling ionization of atoms using a CO2 laser from one of us (SLC) before publication. Since that time this formula has been used as a benchmark for interpretation of practically all experiments and testing theories in the area of strong-field ionization of atoms and molecules. These are only three of many other scientific achievements by N.B. Delone. During his career he published more than 200 papers in scientific journals and a series of 4 books on atoms in a strong laser field and multiphoton processes. These books are used now as manuals in laser-atom physics for students and scientists in many universities and laboratories throughout the world.
N.B. Delone was a great teacher and scientific supervisor. In 2002-2005 he wrote a series of textbooks in Russian for high-school students. For many years he was a lecturer in the Moscow Institute of Physics and Technology. Beginning in 1973 Prof. Delone organized in the General Physics Institute a weekly scientific seminar on multiphoton processes, which still exists and is regularly attended by scientists from various institutes. Prof. Delone had many PhD students from Moscow, Voronezh, Uzhgorod, Tashkent, Tbilisi, Kishinev and other cities of the former Soviet Union. It is practically universal for them to consider Delone as the best teacher they have met in their lives.
After the Soviet Union era, Prof. Delone led a team of Russian scientists in the field of multiphoton physics to collaborate with one of us (SLC) in Canada under the sponsorship of the NATO-linkage program. Many of these scientists quickly expanded their scope of interaction with many other scientists in Canada, the US and Europe. Such collaborations are still going strong and have separated into many teams.
N.B. Delone was always cheerful and enthusiastic in his work although in the 70's he had many complications related to political problems of his son. In spite of this, he kept working. Throughout his career N.B. Delone was a highly creative and respected leader of the multiphoton community in the former Soviet Union and far beyond its borders. He had a gift of arousing enthusiasm in other people. N.B. Delone proved the value of life and left this world forever with a smile.
