Spatio-Temporal Wave-Packet Dynamics Lab
This lab specializes in the field of Physical Optics, where the manipulation of light is used to correlate its spatial and temporal domains. In simpler terms, it means that different colors of light can be directed in specific directions. This technique allows for a greater degree of control and opens up new possibilities for previously unimaginable applications.
In our lab this technique is being employed to do the following:
Space-Time Wave Packets
A beam that has a Gaussian spatial profile experiences diffraction as it propagates. A simple way to understand this is to consider the Gaussian wavepacket as a superposition of plane waves that propagate in many directions; clearly the optic axis plane wave gathers a different amount of phase as the off-axis plane wave with a different angle. This phase difference is indirectly proportional to the wavelength.
There will be interference between iso-frequency plane-waves and the end result is a diffracted beam.
Since phase acquisition is wavelength dependent, what if we instead changed the structure of our beam such that each planewave corresponds to a particular wavelength; in other words, what if we couple the spatio-temporal domains of the wavepacket so that there is no difference in phase and the superposition of plane waves is propagation invariant? That is what a Space-Time Wave Packet is.
1. Grating and lens map the temporal domain along y. At this point there is no relationship between space and time.
2. Spatial Light Modulator applies a phase along x imposing the parabolic space-time relationship we want
3. Lens and grating undoes the mapping from temporal to spatial domain
a. Regular Resonant Cavity
b. Titled Resonant Cavity
c. Omni-Resonant Cavity in which spatiotemporal coupling is achieved using a lens.
A Fabry-Perot cavity is an optical resonator consisting of two parallel mirrors with a small gap between them. Traditionally light that enters the cavity resonates with an extremely narrow spectral line width (1 color only). This can be slightly improved by tilting the cavity to adjust the path length of each wavelength. Since the wavelength that resonates depends on the distance between the two mirrors, using angular dispersion it is possible to make each wavelength experience a different path length and therefore allow a broad range of wavelengths to resonate in the cavity: this is called Omni-Resonance.
Chromatic dispersion resulting from the wavelength dependence of the refractive index is an inescapable feature of optical materials, which leads to pulse broadening and distortion. One may combat its impact via dispersion compensation or dispersion cancellation.
In the former, dispersive broadening and the associated
chirp, a change in the instantaneous frequency, are compensated before or after passage through the medium. More challenging, however, is to neutralize dispersion during passage through a dispersive medium, so that the pulse travels invariantly, which we refer to as dispersion cancellation. Such a capability is crucial, for instance, in enabling efficient nonlinear interactions in long crystals. Our solution to this is to construct our STWP such that it is propagation invariant inside of the media pre-structuring our input.
Typically, solar panels are altered to increase the efficiency of energy generation. However, not many look at altering the structure of the input light to improve the efficiency. Solar panel’s typically depend on incidence angle and wavelength. Using methods of Omni-Resonance we can improve the overall efficiency of solar panels.