Speaker
Description
The coherence of a light source is a key property that is used to determine most of the assumptions we can make about that light source. However, the coherence of light is commonly defined in multiple ways. Practically, the coherence time is often defined as the maximum time difference at which interference fringes are visible when a light source interferes with itself. We can define the coherence time of light sources like continuous wave lasers and thermal sources in this way, even though their coherence times arise from different statistical properties. This difference in statistical properties is important because it changes the measurement of light in many other experiments. For example, the coherence time for thermal light is often measured by the second order coherence, $g^{(2)}(\tau)$. For a thermal source, the $g^{(2)}(\tau)$ goes to the average intensity for $\tau$ that are large compared to the same coherence time at which interference fringes are visible. The $g^{(2)}(\tau)$ for a continuous wave laser is instead constant at the average intensity and does not depend on the coherence time. Pulsed light is multimode, unlike a continuous wave laser, but does not arise from an ensemble of independent sources like thermal light. Physically, this changes how pulsed light is time averaged in a measurement, which also changes how measurement results indicate the statistical properties of the light. We return to the foundations of quantum optics to find the statistics that can describe a beam of multimode light. We then predict the results of common coherence measurements like interference fringes and intensity interference. Based on the known results of these measurements with pulsed light, we determine a general quantum statistical description of pulsed light.
| Keyword-1 | Coherence |
|---|---|
| Keyword-2 | Statistical optics |