[Paper Review] Exciting of surface plasmon polaritons in the Kretschmann configuration

A. P. Vinogradov, A. V. Dorofeenko+2 more|arXiv (Cornell University)|Jul 17, 2017

Plasmonic and Surface Plasmon Research3 references3 citations

TL;DR

The paper challenges the conventional understanding that plane waves incident at angles exceeding total internal reflection can excite surface plasmon polaritons (SPPs) in the Kretschmann configuration. It demonstrates that SPP excitation actually occurs only when a narrow, angularly distributed beam of plane waves is used, where interference of reflected components forms a leaky wave with the SPP wavevector—enabling excitation over a range of angles, not just a single critical angle.

ABSTRACT

We consider a possibility of an excitation of surface plasmon polaritons in the Kretschmann configuration. Contrary to common belief, we show that a plane wave incident at an angle greater than the angle of total internal reflection does not excite surface plasmon polaritons. These excitations do arise, however, if the incident light forms a narrow beam composed of plane waves. As a result of interference of reflected plane wave components, an inhomogeneous (leaky) wave is formed at the edge of the beam. This wave has the wavevector of the surface plasmon polariton if angle of incidence of the beam coincides with the angle at which the minimum of reflection for the plane wave is observed. Since the beam is composed of many plane waves, this condition is satisfied not for just a single angle but for angles over an interval.

Motivation & Objective

• To re-examine the conditions under which surface plasmon polaritons (SPPs) are excited in the Kretschmann configuration.
• To resolve the contradiction between common belief and physical reality regarding SPP excitation by plane waves at angles greater than the critical angle.
• To clarify the role of beam angular spectrum and interference in enabling SPP excitation.
• To identify the precise angular conditions under which SPPs are excited via leaky wave formation.

Proposed method

• Analyzes the reflection of a narrow beam composed of multiple plane waves with varying angles of incidence.
• Applies angular spectrum decomposition to model the beam as a superposition of plane wave components.
• Evaluates interference effects among reflected plane wave components to form an inhomogeneous (leaky) wave at the beam edge.
• Identifies the condition under which the leaky wave's wavevector matches that of surface plasmon polaritons.
• Uses the minimum reflection angle of individual plane waves as a key indicator for SPP excitation.
• Demonstrates that SPP excitation occurs over a range of angles due to the angular spread of the beam, not at a single critical angle.

Experimental results

Research questions

• RQ1 Can surface plasmon polaritons be excited by a single plane wave incident at an angle greater than the critical angle in the Kretschmann configuration?
• RQ2 What physical mechanism enables SPP excitation when a plane wave at such angles fails to excite them?
• RQ3 How does the angular spectrum of a narrow beam influence the formation of leaky waves with SPP wavevectors?
• RQ4 Why is SPP excitation observed experimentally over a range of angles rather than at a single angle?
• RQ5 What role does interference between reflected plane wave components play in enabling SPP excitation?

Key findings

• SPP excitation does not occur for a single plane wave incident at angles greater than the critical angle, contrary to common belief.
• A narrow beam composed of multiple plane waves enables SPP excitation through interference of reflected components.
• The interference generates a leaky wave at the beam edge whose wavevector matches that of surface plasmon polaritons.
• The condition for SPP excitation is satisfied not at a single angle but over a continuous interval of angles corresponding to the beam's angular spread.
• The minimum reflection angle for individual plane waves in the beam corresponds to the onset of SPP excitation.
• SPPs are excited over a range of incident angles due to the beam's finite angular width, explaining experimental observations of broadband SPP excitation.