Observation of Elastic Orbital Angular Momentum Transfer

Elastic Spin and Orbital Angular Momenta

“…Introduction.-Recently, there was a great renewed interest in the spin and orbital angular momenta of acoustic waves, i.e., sound waves in fluids or gases [1][2][3][4][5][6][7][8] and elastic waves in solids [9][10][11][12][13][14][15]. Although general fieldtheory principles of the momentum and angular momentum of sound and elastic waves have been known [16][17][18], and the orbital angular momentum of sound waves was extensively studied both theoretically and experimentally [19][20][21][22][23][24][25][26][27][28], new observable phenomena involving spin-polarization properties of sound waves, as well as the spin and orbital angular momenta of elastic waves, prompted a new wave of investigations in these fields.…”

“…This work is motivated by the recent papers [14,15] which calculated the orbital angular momentum of elastic wave modes in an isotropic cylinder and reported its observation. We revisit the canonical momentum, spin, and orbital angular momentum of elastic waves in an isotropic medium using the field-theory approach [4,8,10,17], which has been successfully employed in optics [29][30][31][32][33][34].…”

“…We find that theoretical results of Refs. [14,15] contain significant errors, and show that the canonical momentum and angular momentum of elastic waves are described by rather simple general expressions, which do not require separation of the longitudinal (compression) and transverse (shear) parts of the wavefield. Moreover, the longitudinal, transverse, and 'hybrid' contributions contained in these general expressions are equally important and cannot be neglected (as it was done in Refs.…”

“…Moreover, the longitudinal, transverse, and 'hybrid' contributions contained in these general expressions are equally important and cannot be neglected (as it was done in Refs. [14,15]).…”

“…( 2)-( 4) differ from the recent results of Refs. [14,15]. To show this, from now on we consider monochromatic wavefields and introduce the complex-amplitude representation for the wavefields: a(r, t) = Re a(r)e −iωt , v(r, t) = Re v(r)e −iωt , where v = −iωa.…”