Abstract

It is typically assumed that the fluctuations associated with a stationary broadband incoherent field propagate in free space at the speed of light in vacuum $c$. Here we introduce the concept of “coherence group velocity” which, in analogy to the group velocity of coherent pulses, is the speed of the peak of the coherence function. We confirm experimentally that incorporating a judicious spatio-temporal spectral structure into a field allows tuning its coherence group velocity in free space. Utilizing light from a superluminescent diode, we interferometrically measure the group delay encountered by the cross-correlation of a structured field synthesized from this source with the unstructured diode field. By tracking the propagation of this cross-correlation function, we measure coherence group velocities in the range of $12c$ to $-6c$.

© 2019 Optical Society of America

Space–time wave packets that travel in optical materials at the speed of light in vacuum

Basanta Bhaduri, Murat Yessenov, and Ayman F. Abouraddy
Optica 6(2) 139-146 (2019)

What is the maximum differential group delay achievable by a space-time wave packet in free space?

Murat Yessenov, Lam Mach, Basanta Bhaduri, Davood Mardani, H. Esat Kondakci, George K. Atia, Miguel A. Alonso, and Ayman F. Abouraddy
Opt. Express 27(9) 12443-12457 (2019)

Broadband space-time wave packets propagating 70  m

Basanta Bhaduri, Murat Yessenov, Danielle Reyes, Jessica Pena, Monjurul Meem, Shermineh Rostami Fairchild, Rajesh Menon, Martin Richardson, and Ayman F. Abouraddy
Opt. Lett. 44(8) 2073-2076 (2019)

Non-diffracting broadband incoherent space–time fields

Murat Yessenov, Basanta Bhaduri, H. Esat Kondakci, Monjurul Meem, Rajesh Menon, and Ayman F. Abouraddy
Optica 6(5) 598-607 (2019)

Oscillatory trajectory of an optical beam propagating in free space

Octávio J. S. Santana and Luís E. E. de Araujo
Opt. Lett. 44(3) 646-649 (2019)