Excitation of large-amplitude electron plasma wave by counterpropagation of two laser beams in spherical nanoparticles

Abstract The counterpropagation interaction of two different laser beams with a spherical nanoparticle medium is used to excite a large-amplitude electron plasma wave. The two laser beams having slightly different frequencies cause beat wave generation at the beat wave number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>k</mml:mi> <mml:mo>=</mml:mo> <mml:mrow> <mml:msub> <mml:mi>k</mml:mi> <mml:mn>1</mml:mn> </mml:msub> </mml:mrow> <mml:mo>+</mml:mo> <mml:mrow> <mml:msub> <mml:mi>k</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> and beat wave frequency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>ω</mml:mi> <mml:mo>=</mml:mo> <mml:mrow> <mml:msub> <mml:mi>ω</mml:mi> <mml:mn>1</mml:mn> </mml:msub> </mml:mrow> <mml:mo>−</mml:mo> <mml:mrow> <mml:msub> <mml:mi>ω</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> . The high-power laser beam radiation ionizes the atoms of the nanoparticles and subsequently converts them into plasma plume balls. The gradient in the field of each laser beam is considered to be responsible for the generation of a nonlinear ponderomotive force to the conduction electrons associated with a cloud of nanoparticles. This nonlinear force has the potential to couple and drive an immense amplitude of electron plasma waves. Due to the presence of surface plasmon resonance on the spherical nanoparticle surface, as the beat wave of two electromagnetic beams approaches <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> times the electron plasmon frequency, resonant coupling of electron plasma waves occurs. The power amplitude of the excited electron plasma wave is strongly dependent on the laser parameters and interaction medium parameters. By optimizing and controlling the above parameters, the required power amplitude of the electron plasma wave can be excited. This immense amplitude excitation of the electron plasma wave process could be applied to obtainenhanced laser harmonic generation, anomalous electron heating, self-focusing and laser absorption processes.