thermoreflectance imaging

**Thermoreflectance Imaging** is a **non-contact thermal mapping technique** — that measures the tiny change in surface reflectivity caused by temperature variations. The reflectivity of metals and semiconductors changes linearly with temperature (thermoreflectance coefficient $kappa$). **How Does It Work?** - **Principle**: $Delta R / R = kappa cdot Delta T$. Typical $kappa approx 10^{-4}$ to $10^{-5}$ per Kelvin. - **Detection**: A CCD camera images the surface under LED illumination. Changes in reflected intensity map to temperature. - **Lock-In**: Often combined with lock-in detection to extract the tiny $Delta R$ from noise. - **Resolution**: Diffraction-limited (~300 nm with visible light). **Why It Matters** - **Non-Contact**: No coating required (unlike FMI or liquid crystal). - **Speed**: Can capture transient thermal events (nanosecond pulsed measurements). - **Applications**: Laser diode characterization, power amplifier thermal mapping, IC hot spot detection. **Thermoreflectance Imaging** is **seeing heat through reflection** — converting invisible temperature changes into measurable optical signals.