Incoherent "slow and fast light".

Area of Science:

• Nonlinear Optics
• Quantum Optics
• Materials Science

Background:

• The phenomena of "slow light" and "fast light," characterized by pulse delay and advancement, are typically studied under conditions of coherent population oscillations (CPO).
• These effects are often interpreted as evidence of modified light group velocity within a medium.

Purpose of the Study:

• To investigate whether the effects attributed to CPO and "slow light" can be replicated using incoherent light sources.
• To determine if observed pulse delays and spectral changes are sufficient indicators of altered group velocity.

Main Methods:

• Experimental setup utilizing an incandescent lamp as an incoherent light source.
• Study of nonlinear optical responses in photochromic glass and thermochromic coating materials.
• Analysis of the objects' response to intensity-modulated incident light.

Main Results:

• The experimental observations with incoherent light fields closely reproduced the characteristic features of "light with a negative group velocity" and "ultraslow light."
• The observed pulse delay and spectral modulation changes mirrored those typically associated with CPO-based "slow light" experiments.
• Pure-intensity nonlinearity in the materials was sufficient to generate these observed effects.

Conclusions:

• The "slow and fast light" effects, previously attributed to CPO, can be universally observed with incoherent light and pure-intensity nonlinearity.
• Observed pulse delay and spectral modulation changes are not conclusive evidence for modifications in the light group velocity of a medium.