Laser - matter interactionsBoris Lukiyanchuk

Singapore, 26 November 2018

Lecture 6.

Laser - matter interactions

Nonresonant processes Resonant processes

Physical Processes

Laser Thermochemistry

Vapor PlasmaProcesses

Plasmonics Photonics

NonlinearOptics

Resonant Chemistry

Lecture 6. Resonant Laser Chemistry

Lecture 1 Lecture 3 Lecture 2Lecture 5

Lecture 4

“The School of Athens” a fresco of Raphael in

the Papal Palace of the Vatican.

Leonardo da Vinci

1446 – 1523

Michelangelo

1475 – 1564Raphael

1483 – 1520Niccolò Machiavelli

1469 – 1527Plato walks alongside Aristotle

Raphael was the main architect of the St. Peter Cathedral.

Aristotle

384–322 BC

Plato

423 – 347 BC

Socrates

470-399 BC

Observation, reason, and experiment make up what we

call the scientific method.

Richard Feynman

Aristotle wrote the book “Physics”, where he gave thedefinition of matter and discuss the possible reasons ofthe matter transformations.

Antoine Lavoisier

1743 – 1794

The Feynman Lectures on Physics

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one

sentence passed on to the next generations of creatures, what statement would contain the

most information in the fewest words? I believe it is the atomic hypothesis (or the

atomic fact, or whatever you wish to call it) that all things are made of atoms—little particles

that move around in perpetual motion, attracting each other when they are a little distance

apart, but repelling upon being squeezed into one another.

Mikhail Lomonosov

1711 – 1765Stanislao Cannizzaro

(1826 – 1910)

John Dalton

1766 – 1844

They proposed the concept that substances consist of atoms.

Henry Eyring

1901 – 1981Michael Polanyi

1891 – 1976

In 1935 Eyring, and Polanyi developed the "activated-complex theory“. The theoretical

assumption was that the transition state was crossed very rapidly, on the time scale that applies to

molecular vibrations. That it would ever be possible to perform experiments over such short

times was something no-one dreamed of.

Quantum theory has shown that the existence of chemical forces is a direct consequence of the

laws of quantum mechanics.

A chemical reaction is a process that leads

to the chemical transformation of one set

of chemical substances to another.

Chemical reactions are accompanied by a

lost or release of energy.

George Porter

1920 – 2002

1967

Manfred Eigen

1927 -Ronald Norrish

1897 – 1978

19671967

"for their studies of extremely fast chemical reactions, effected by

disturbing the equilibrium by means of very short pulses of energy"

Flash photolysis is a pump-probe laboratory

technique, in which a sample is firstly excited by a

strong pulse (called pump pulse) of light by a

short-pulse light source such as a flash lamp. This

first strong pulse starts a chemical reaction or

leads to an increased population for energy levels

other than the ground state within a sample of

atoms or molecules.

Temporal resolution of flash photolysis

was on the level 10−3𝑠..

Walter Kohn

"for his development of the

density-functional theory"

John A. Pople

"for his development of computational

methods in quantum chemistry."

1998

Ahmed Zewail (1946 – 2016)

1999

"for his studies of the transition states of chemical

reactions using femtosecond spectroscopy"

1992

Rudolph A. Marcus

1923 -

"for his contributions to the theory of electron

transfer reactions in chemical systems"

RRKM theory

The Rice–Ramsperger–Kassel-Marcus (RRKM)

theory is a theory of chemical reactivity. It took

the transition state theory into account.

Assume that the molecule consists of harmonic

oscillators, which are connected and can exchange

energy with each other.

Assume the possible excitation energy of the molecule

to be E, which enables the reaction to occur.

The rate of intra-molecular energy distribution is

much faster than that of reaction itself.

Vladilen Letokhov

1939 - 2009

more than 850 scientific articles and 14 monographs in the field of laser

physics, spectroscopy, chemistry, biomedicine and astrophysics related with lasers.

Laser trapping

Laser cooling

Laser chemistry

Optical frequency standards

1997

Steven Chu

1948

Cohen-Tannoudji

1933William Phillips

1948

1999Ahmed Zewail

1946 – 2016

Roy Glauber

2005Letokhov Chebotaev 1978

Arthur Ashkin2018

Science, 180, pp. 451 - 458(May 4, 1973)

The main processes of the selective laser photophysics and photochemistry are:

I. selective separation of substances at the atomic and molecular levels;

II. selective chemical reactions with atoms or molecules of the desired kind (for chemical

separation) or in the desired direction (photochemical synthesis);

III. selective detection of atoms, molecules, or molecular bonds.

Types and areas of application of processes In selective laser photophysics and photochemistry.V. S. Letokhov, Sov. Phys. Uspekhi 21, pp. 57-96 (1978)

ELEMENTARY SELECTIVE PHOTOPROCESSES

Properties of atoms and molecules altered by excitation with laser radiation: 1) increase of

reactivity; 2) reduction in ionization energy; 3) reduction in dissociation energy; 4)

predissociation; 5) isomerization; 6) change in trajectory of motion.

Main methods of selective interaction of laser radiation with atoms and molecules

Atoms Molecules

1. photochemical reaction; 2. ionization;

3. change in the velocity or deflection of

a trajectory of selectively excited atoms.

2+. Two other methods:

selective photodissociation of molecules

and photoisomerization.

a) selective two-step photoionization of atoms; b) selective two-step photodissociation of

molecules and comparison with photochemical processes.

Types of photoexcitation

a) one-step excitation of an

electronic or vibrational

state; b) two-step excitation

of an electronic state via an

intermediate vibrational or

electronic state; c)

multiphoton excitation by

infrared radiation.

Comparison of Different Photochemical Molecular Processes.

Photochemical separation of

mercury atoms, based on an

increase in the rate of reaction

of the excited mercury atoms

(A*) with oxygen (acceptor R).

W. Kuhn and H. Martin,

Naturwissenschaften 20, 772

(1932); Z. Phys. Chem. Abt. Β

21, 93 (1933).

However, the case of the

mercury atoms is exceptional

because of the existence of

metastable triplet states and

high-intensity mercury lamps.

PHOTOPHYSICAL ISOTOPE SEPARATION METHODS

a) two-step photoionization; b) three-step photoionization; c) two-step photoionization via an

autoionizing state; d) two-step selective excitation of a Rydberg state and its photoionization by IR

radiation; e) two-step selective excitation of a Rydberg state and its ionization by an electric field.

A common feature of all the selective ionization schemes is the following sequence of processes: 1)

selective excitation; 2) ionization of the excited atoms.

The first successful selective two-step ionization of atoms (of rubidium): JETP Lett. 13, 217 (1971)Separation of uranium isotopes: Livermore Laboratory: IEEE J. Quantum Electron. QE-10, 790 (1974).

Selective two-step (IR + UV) photodissociation

The two-step photodissociation of molecules is more complex than the two-stepphotoionization of atoms because of the following effects which influence the selectivity andrate of the process: l) the thermal nonselective excitation of vibrational levels; 2) thesmearing out of the edge of the electronic photoabsorption band of molecules; 3) thebottleneck effect due to the rotational structure of vibrational levels. The first two effectsrestrict the dissociation selectivity and the third sets an upper limit to the rate of absorptionof IR radiation by a molecule and, consequently, to the rate of the two-step photodissociationof molecules in a gas.

a) two-step IR + UV photodissociation; b) multistep selective excitation of high vibrational levels and theirphotodissociation by UV radiation; c) multiphoton selective excitation and dissociation by a single-frequency intense IR field; d) multiphoton selective excitation of vibrational levels by a resonant IR fieldand multiphoton dissociation of these levels by nonresonant intense IR radiation.

Multiphonon dissociation of molecules

It utilizes only high-power IR laser radiation for the direct excitation of very high vibrationallevels in the ground electronic state: isotopically selective dissociation of polyatomicmolecules (BCl3, SF6, OsO4 and others) by high-intensity CO2 laser pulses.

a) selective multistep excitation by triplevibrational-rotational resonance andsubsequent excitation of molecules in"vibrational quasicontinuum"; b) selectiveexcitation due to triple resonance followedby "leakage" to the vibrationalquasicontinuum.

Isotopic effect in the bands of nitromethane:

linear absorption spectrum at 20 Torr. CH315NO2

(solid) CH314NO2 (dashed).

The various transitions in themolecule's rotational quantumnumber J. R-branch correspondsto J = + 1, the P-branch to J = - 1 ,and the Q-branch to J = 0.

Dissociation of a diatomic molecule in a strong laser field: G. A.

Askaryan, Sov. Phys. JETP 19, 273 (1964); 21, 439 (1965); F. V.

Bunkin, R. V. Karapetyan, A. M. Prokhorov, Sov. Phys. JETP 20,

145 (1965).

Gurgen Askaryan

1928 – 1997Fedor Bunkin

1929-2016

Prokhorov 1916 - 2002

A. Prokhorov

1916 - 2002

PHOTOCHEMICAL ISOTOPE SEPARATION METHODS

1. Electronic photochemistry (subject of research before the appearance of lasers).2. Vibrational photochemistry (selective excitation of vibrational levels of molecules).

a) absorption of one photon in the fundamental band; b) absorption of one photon in thesecond overtone; c) two-step excitation in a two-frequency IR field; d) Raman excitation of avibration inactive in infrared absorption giving rise to two-frequency visible laser radiation;e) multiphoton excitation of high vibrational levels by single frequency intense IR radiation.

PREPARATION OF PURE SUBSTANCES

Selective dissociation of molecules

Purification of AsCl3 gas by selective dissociation of CCl4 and

C2H4Cl2 impurity molecules by CO2 laser radiation. The

absorption bands of the C2H4Cl2 and CCl4 impurity molecules

lie in the CO2 laser emission range, where there are no

absorption bands of the main substance AsCl3.

SELECTIVE LASER BIOCHEMISTRY

Selective excitation and breaking of hydrogen bonds in DNA

The double helix of DNA is formed by hydrogen bonds

between the guanine—cytosine and adenine— thymine

bases. Breaking of these hydrogen bonds should split the

double helix into two identical chains and result in

subsequent replication of DNA.

Excitation of levels by IR laser radiation to

stimulate proton tunneling.

SELECTIVE DETECTION OF NUCLEI,

ATOMS, AND MOLECULES

a) transition scheme; b) change in photoionization

cross section of selectively excited molecules.

An infrared mass spectrometer promises to be auniversal, highly selective, and very sensitivedetector of complex molecules, which may proveuseful in many scientific and technicalapplications. In fact, since the detection of excitedmolecules by photoionization is highly sensitive, itshould be possible to determine the IR spectra ofextremely small amounts of matter, much smallerthan those that can be tackled by the best existingclassical and laser infrared spectrometers.

SPATIAL LOCALIZATION OF MOLECULAR BONDS

A laser ion microscope for spatiallocalization of molecular bonds.

The function of the electric field is only to

transfer electrons or ions along radial

trajectories to the projector screen. The

selective photoionization of specific

molecular bonds in a macromolecule, which

is located on the tip of the projector, is

performed in accordance with the multistep

scheme using several picosecond laser

pulses with specially selected frequencies.

Vladimir Akulin

V. M. Akulin, N. V. Karlov, Boris S. Luk'yanchuk

Nonthermal Stochastic Behavior of Polyatomic

Molecules under the Action of Resonance

Laser Field Resulting from the Presence of

Special Domains in the Phase Space of

Vibrational VariablesBulletin of the Academy of Sciences of the U.S.S.R,

Physical series 47 (8), pp.1573-1577 (1983)

Vibrational motion of a highly excited molecule. Dynamics of excitation

of coupled anharmonic oscillators under the action of a resonant external

force. The calculation results show the absence of thermal energy

distribution over molecule degrees of freedom. The trajectory, starting from

a certain region of the phase space, continues to remain in this region for a

long time. Movement of the molecule is stochastic. The impact of quantum

fluctuations is especially important in areas of a “tangle type” on a phase

trajectory.

The acquired energy of the molecule vs time for different levels of fluctuations.

The projection of the phase trajectory on the plane {I,J).

Laser action selectivity and diffusion control

Pyotr Lebedev 1866-1912measure the pressure of lighton a solid body in 1899

Ashkin's greatest achievements

were to come in the study of

radiation pressure—the idea that

light and other forms of radiation

can exert a force on objects.

2018

Anatoly Shalagin

F. Gelmukhanov, A. ShalaginLight-induced diffusion of gases

JETP Lett 29, 711 (1979)

The traveling light wave produces

a macroscopic flux of absorbing

particles, if they are mixed with a

buffer gas. The flux is directed

either forward of propagating

wave or away from it.

P mv

F I

Because of the Doppler effect, the atoms whose velocities satisfied

the condition - mn = kv interact most effectively with thefield. If << kv Bennett peaks and dips. > kv sum ofequilibrium (Maxwellian) and antisymmetric parts. Jn and Jm fluxesbuck each other. If the gas of absorbing atoms is mixed with thebuffer gas, then the partial fluxes set in motion of absorbing gas as awhole (dimension of atom in the ground state and excited state aredifferent).

F - mn

Laser action selectivity and thermal diffusion with positive feedback

Carl Ludwig

1816-1895

Thermophoresis (also thermodiffusion, the Soret

effect, or the Ludwig–Soret effect) is a

phenomenon observed in mixtures of mobile

particles where the different particle types

exhibit different responses to the force of

a temperature gradient.Ludwig discovered

thermophoresis in

liquid in 1856

T1 T2

Charles Soret

1854 – 1904

Soret understood

thermodiffusion

in 1879

John Tyndall

1820 –1893

M. Faraday

Thermophoresis in gas mixtures

1870

Sydney Chapman

1888 – 1970Lord Rayleigh

1842–1919

1904

James Maxwell

1831–1879

Ludwig Boltzmann

1844 - 1906

The Dufour effect (found in 1872) is

the energy flux due to a

mass concentration gradient occurring

as a coupled effect of irreversible

processes. It is the reciprocal

phenomenon to the Soret effect.

Louis DuFour

1832–1892

Lars Onsager

1903-1976

1968

"for the discovery of the

reciprocal relations bearing his

name, which are fundamental

for the thermodynamics of

irreversible processes."

The diffusion flux I and the heat flux

are due to the presence of

concentration and temperature

gradients

i = - α grad μ - β grad T,

q = - δ grad μ - γ grad T + μ i

See L.L. Fluid Mechanics, § 59

𝝏𝒄

𝝏𝒕= 𝑫∆𝒄

𝝏𝑻

𝝏𝒕= 𝝌∆𝑻

𝒅𝒄

𝒅𝒙=

𝑫𝑻

𝑫

𝟏

𝑻

𝒅𝑻

𝒅𝒙=

𝑫𝑻

𝑫

𝒅

𝒅𝒙l𝑜𝑔 𝑇 , where

𝑫𝑻

𝑫= α c (1− c), α is thermodiffusion coefficient.

Let us consider concentrations of components within the mixture of two gases as c and 1-c. established

gradient of concentration is

α ≈𝒎𝟐 −𝒎𝟏

𝒎𝟐 +𝒎𝟏

𝒏 − 𝟓

𝒏 − 𝟏here n is an exponent in the asymptotic of the repulsive force

between molecules ∝ = Τ1 𝑟𝑛 .

𝑑𝑐

𝑑𝑥= α c (1− c)

𝑑

𝑑𝑥ln𝑇 , or

𝑑𝒄

c (1− c)= α 𝑑 ln𝑇

𝒄

1− c= 𝑨𝑻𝜶

Considering 𝑐 = 𝑐1 at 𝑇 = 𝑇1 and 𝑐 = 𝑐2 at 𝑇 = 𝑇2 we find

𝑐1

1−𝑐1/

𝑐2

1−𝑐2=

𝑇1

𝑇2

𝒂≈ 1 + 𝛼 log

𝑇1

𝑇2

G. Müller & G. Vasaru,

The Clusius-Dickel Thermal

Diffusion Column – 50

Years after its Invention,

Isotopenpraxis Isotopes in

Environmental and Health

Studies 24, pp. 455-464

(1988).

F. V. Bunkin, N. A. Kirichenko, B. S. Luk'yanchuk

Diffusion instability in a laser radiation field

Sov. J. Quantum Electron. 13, 1430 (1983)

T (t = 0) = 𝑇𝑤 ,𝑛 𝑡 = 0 = 𝑛0

Latest results

Thermophoresis at solids interfaces:

Schoen P. A. E. et al, Nanoparticle Traffic on Helical Tracks: Thermophoretic Mass Transportthrough Carbon Nanotubes, Nano Letters 6 (9), pp. 1910–1917 (2006) – theory.

Barreiro A. et al, Subnanometer motion of cargoes driven by thermal gradients along carbonnanotubes, Science 320, pp. 775–778 (2008) - experiment.

Negative thermophoresis in fluids:

Dwyer H. A., Thirteen‐Moment Theory of the Thermal Force on a Spherical Particle, Physics ofFluids 10, pp. 976–984 (1967) - theory.

Sone Yoshio, A Flow Induced by Thermal Stress in Rarefied Gas, Journal of the Physical

Society of Japan. 33, pp. 232–236 (1972).

Negative thermophoresis at solids interfaces

Leng Jiantao et al, Negative Thermophoresis in Concentric Carbon Nanotube Nanodevices, Nano Letters 16, pp. 6396–6402 (2016).

Literature

1. V. S. Letokhov,

Laser Control of Atoms and Molecules,

Oxford University Press, 2007

2. V. M. Akulin,

Dynamics of Complex Quantum Systems,

Oxford University Press, 2007

3. Rolf Haase,

Thermodynamics of Irreversible processes,

Dover, 1990