Femtosecond Laser-Matter Interactions: Solid-Plasma-Solid Transformations at the Extreme Energy Density

Cover
Half Title
Title Page
Copyright Page
Dedication
Table of Contents
Preface
List of frequently used symbols
Chapter 1: Basics of Laser–Matter Interactions: Light and Matter
	1.1: Laser Beam
		1.1.1: Macroscopic Electrodynamics
		1.1.2: Polarization States
		1.1.3: Spectral Structure
		1.1.4: Temporal/Spatial Shape of the Incident Laser Pulse Intensity
		1.1.5: Focussing Positions of the Laser Beam on/in a Target
		1.1.6: Focussing to Diffraction Limit with the High NA Lens
		1.1.7: Diffraction-Free Beams
	1.2: The Matter
		1.2.1: Electrons’ Oscillations and Scattering in the High-Frequency Electromagnetic Field
		1.2.2: The Drude Model for the Permittivity of Simple Plasma in the High-Frequency Electric Field
			1.2.2.1: Electrons’ plasma frequency
			1.2.2.2: Critical density of electrons
		1.2.3: Absorbed Energy Density
		1.2.4: Hierarchy of the Laser-Affected Material Transformations as a Function of Laser Intensity/Fluence
			1.2.4.1: Melting
			1.2.4.2: Ablation
			1.2.4.3: Atomic field intensity
			1.2.4.4: The relativistic intensity
	1.3: Summary
Chapter 2: Interaction with Metals
	2.1: Interaction of the Plane Wave with a Metal Layer
	2.2: Electron and Lattice Temperature, Energy Balance, Two-Temperature Approximation
	2.3: Temperature Dependence of the Electronic and Lattice Heat Capacity
	2.4: Electrons Relaxation Processes in the Laser-Affected Metal
		2.4.1: Electron–Electron Collisions
		2.4.2: Electron–Phonon Momentum Transfer
		2.4.3: Electron–Phonon Energy Transfer
		2.4.4: Electron-to-Ion Momentum and Energy Transfer
		2.4.5: Electron-to-Ion Energy Exchange Time
			2.4.5.1: Non-ideality effects
			2.4.5.1: Effects of the oscillations in high-frequency electromagnetic field on the electrons’ collision rate
	2.5: Modification of the Electron Distribution Function:  From the Fermi–Dirac to the Maxwell–Boltzmann
	2.6: Electronic Heat Conduction
	2.7: Summary
Chapter 3: Interaction with Dielectrics
	3.1: Ionization in the Strong High-Frequency Electric Field:  Electrons Transfer from the Valence to Conduction Band and to Continuum
		3.1.1: Tunnelling Ionization Rate in the Limit y << 1
			3.1.1.1: Linear polarization
			3.1.1.2: Tunnel ionization in the elliptically polarized electric field
		3.1.2: Multi-Photon Ionization Rate
			3.1.2.1: Linear polarization
			3.1.2.2: Time dependence of the ionization degree produced by the Gaussian laser pulse with the MPI domination
			3.1.2.3: Circular polarization
		3.1.3: Ionization by the Electron Impact
			3.1.3.1: Transition to the avalanche regime
		3.1.4: Distribution Function of Electrons Transferred to the Conduction Band in Dielectrics
	3.2: Electrons’ Collision Rates:  Momentum and Energy Transfer
		3.2.1: Electron–Phonon Collisions
		3.2.2: Momentum and Energy Transfer Collisions in a Dielectric Converted to Plasma
		3.2.3: Effects of the Electrons’ Oscillations in the HF Field on the Collision Rates
	3.3: Transient Permittivity in the Laser-Affected Dielectric
		3.3.1: Non-Linear Contributions to the Permittivity at the Low Intensity (I << Iat)
		3.3.2: Kerr-Nonlinearity in Silica:  Temperature Dependence
		3.3.3: Permittivity in the Intense-Laser-Excited Dielectric
			3.3.3.1: Reaching the state Ɛre = 0
	3.4: Laser Interaction with the Electrically Inhomogeneous Dielectric
		3.4.1: Normal Incidence
		3.4.2: Oblique Incidence
			3.4.2.1: s-Polarization
			3.4.2.2: p-Polarization
			3.4.2.3: Band gap modification and collapse
	3.5: Energy Density Thresholds for Achieving the Major Steps in Dielectric-Plasma Transformation
		3.5.1: Threshold to Achieve the State Where Ɛre = 0
		3.5.2: Threshold Fluence for Transferring All Valence Electrons to the Conduction Band
		3.5.3: Ionization Threshold:  Transfer Electrons to the Solid Plasma State
	3.6: Energy Equations:  Two-Temperature Approximation
	3.7: Linear and Non-Linear Heat Conduction:  Transition from Heat Transfer in Solid to That in Plasma
		3.7.1: Heat Diffusion in the Isotropic Medium
		3.7.2: Thermal Conduction in Dielectrics:  Energy Carriers are Phonons
		3.7.3: Electronic Heat Conduction in Plasma
		3.7.4: Applicability of Diffusion Approximation for Description the Heat Conduction in the Laser-Created Plasma
		3.7.5: Linear and Non-Linear Heat Propagation from the Focal Region
			3.7.5.1: Linear heat conduction
			3.7.5.2: Non-linear heat propagation
	3.8: Summary
Chapter 4: Non-Destructive Transformations:  Formation, Lifetime and Decay of Unconventional States of Matter
	4.1: Generation and Decay of the Coherent Phonons
		4.1.1: Melting in Equilibrium:  Atomic Vibrations Become Anharmonic
		4.1.2: Swift Deposition of the Energy Density Comparable to the Enthalpy of Fusion by the Ultra-Short Laser Pulse
			4.1.2.1: Processes during the pulse:  building the electronic pressure force
			4.1.2.2: After the end of the pulse:  electronic heat transfer, electron–lattice temperature equilibration, and phonon’s decay rate
			4.1.2.3: Phonon’s excitation imprinted into the transient optical properties
			4.1.2.4: Experiments
	4.2: Fast Transformations in Non-Equilibrium:  Transient Phase States—Neither Solid Nor Melt
		4.2.1: Road to Melting in Equilibrium:  Sequence of the Catastrophes
			4.2.1.1: Main features of the melting in equilibrium
			4.2.1.2: Critical entropy and critical temperature
		4.2.2: Ultra-Fast Material Transformations
			4.2.2.1: The legitimacy of the entropy concept for the description of rapidly excited metal
			4.2.2.2: Entropy changes during the quick heating
		4.2.3: Novel Transient Phase States—Neither Solids Nor Melts
			4.2.3.1: Excitation of metals/semi-metals—Ga, Bi, Al
	4.3: Mixed Dielectric/Metal Properties in Swiftly Excited Transparent Dielectric
	4.4: Inverse Population in Laser-Excited Sapphire and Silica
	4.5: Summary
Chapter 5: Ablation of Metals and Dielectrics
	5.1: Evaporation in Equilibrium
	5.2: Major Relaxation Processes under Swift Short Pulse Excitation
	5.3: Short Pulse Ablation Thresholds
		5.3.1: Ablation of Metals
			5.3.1.1: Extremely short pulses of duration shorter tc,i
			5.3.1.2: Comparison to the Coulomb explosions of clusters
			5.3.1.3: Ultra-short pulses ω-1pi < tp < theat
			5.3.1.4: Ablation threshold fluence for metals
		5.3.2: Ablation of Dielectrics
	5.4: Dependence of the Ablation Thresholds on the Laser Wavelength for Metals and Dielectrics
	5.5: Long Pulse Ablation Thresholds
	5.6: Ablation Thresholds in the Ambient Gas
	5.7: Ablation Rate, Depth and Mass Per Single Pulse
	5.8: Control over the Phase State of the Ablated Plume
		5.8.1: Criterion for Complete Atomization of Ablated Plume
		5.8.2: Experimental Verification of the Plume’s Atomization
	5.9: Multiple Pulse Action:  Accumulation Effects
		5.9.1: Dwell Time:  Control over the Number of Pulses Hitting the Spot
		5.9.2: Multiple-Pulse Action on Dielectrics:  Energy Accumulation
		5.9.3: Achieving Thermal Ablation Threshold with the Low-Energy Multiple Pulses
		5.9.4: Smoothing of the Intensity Distribution across the Focal Spot
		5.9.5: Change of the Interaction Mode:  Density Build-Up near the Target Surface
	5.10: Summary
Chapter 6: Extreme Energy Density Confined inside a Transparent Crystal—Novel Path for New Materials Creation:  Solid-Plasma-Solid Transformations
	6.1: Introduction
	6.2: Interaction of the Gauss Beam Tightly Focused inside a Transparent Crystal
		6.2.1: Beam Propagation
		6.2.2: Focusing of the Gauss Beam with the High-NA Optics
			6.2.2.1: Conventional approach to the high-NA focusing
			6.2.2.2: Experimental evidence:  high-NA focus produces nano-sharp intensity distribution
		6.2.3: Laser Modification of the Dielectric Permittivity:  Conversion to Solid Density Plasma
			6.2.3.1: Threshold for Conversion of Dielectric into Absorbing Medium (εre = 0)
			6.2.3.2: Conversion a dielectric to the solid density plasma
			6.2.3.3: Ionization after the end of the pulse
		6.2.4: Relaxation Processes
			6.2.4.1: Range for the maximum temperature/pressure value in the absorption volume
			6.2.4.2: Ion’s acceleration by the gradient of the electronic pressure
			6.2.4.3: Electrons-to-ions energy transfer by the Coulomb collisions:  Spatial separation of the light and heavy ions
			6.2.4.4: Diffusion of ions with the different masses:  The experimental evidence of the spatial separation
		6.2.5: Micro-Explosion in Sapphire Considered as a Strong Point-Like Explosion
			6.2.5.1: Interpretation of the micro-explosion experiments using the strong point-like explosion solution
		6.2.6: Summary of the Conditions after the Electron–Ion Energy Equilibration Shock Wave Generation, Propagation and Stopping
			6.2.6.1: Analysis of the experimentally observed structure on the basis of the energy and mass conservation laws
			6.2.6.2: Evolution of the conditions and the structure of the laser affectedzone during expansion
		6.2.7: Modelling the Hydrodynamics of the Confined Explosion
		6.2.8: Relaxation of the Laser-Affected Material to the Ambient Conditions
	6.3: Interaction of the Gauss Beam Tightly Focused on the Surface of an Opaque Solid Buried under the Transparent Cover
		6.3.1: Upper Limit for the Energy Density Directly Delivered to the Opaque Medium through the Transparent Layer
		6.3.2: High-Energy-Density Interaction at the Silicon/Silica Interface
		6.3.3: Shock Wave Generation in Silica Layer
	6.4: Summary of the Gauss Beam–Generated Confined Micro-Explosions
	6.5: Interaction of the Bessel Beam Focused inside a Bulk of the Transparent Crystal
		6.5.1: Status of the BB–Transparent Crystal Interactions
		6.5.2: Non-Diffractive Bessel Beam
		6.5.3: Creation of the BB by the Circular Slit
		6.5.4: Formation the BB by Transmitting the GB through the Axicon
		6.5.5: BB Interaction with the Transparent Medium at Low Intensity
		6.5.6: Intense BB Interaction:  Conversion a Dielectric into Plasma Near the Axis
		6.5.7: BB Interaction with Plasma
		6.5.8: Energy Deposition in Plasma to the End of the Pulse
		6.5.9: Strong Cylindrical Explosion
		6.5.10: Experimental Evidence of the High Energy Density Achieved by the BB Induced Cylindrical Explosion
	6.6: Solid-Plasma-Solid Transformation in Confined Micro-Explosion:  New Path for High-Pressure Material Phase Formations
		6.6.1: Discovery of Superdense bcc-Al in Sapphire Irradiated by the Tightly Focused Gauss Beam
		6.6.2: Discovery of New Tetragonal Polymorphs of Silicon
	6.7: Summary:  Confined Micro-Explosion by the Gauss and Bessel Beams
Conclusions and Future Directions
Appendices
Bibliography
Index