Boyd, a pioneer in nonlinear optics, reminds us that lasers break the rules of traditional radiometry. Incoherent light (like an LED or a bulb) spreads out. Coherent light (laser) can be focused to a diffraction-limited spot, achieving enormous irradiance.
When detecting a laser, the spatial coherence changes the statistics of the photons (from Poissonian to Bose-Einstein in some cases), which affects how you calculate the noise floor.
Robert W. Boyd's 1983 textbook, "Radiometry and the Detection of Optical Radiation," offers a foundational, 14-chapter overview of electromagnetic radiation, blackbody theory, and sensor noise analysis, bridging radiative transfer with modern detection systems. Widely used in optical engineering, it provides comprehensive, mathematically rigorous content on topics ranging from the Radiance Theorem to specific photoemissive and thermal detector mechanisms. A preview of the content is available through the NASA ADS link radiometry and the detection of optical radiation boyd pdf
Radiometry and the Detection of Optical Radiation - Wiley-VCH
Unlike standard optics textbooks that focus heavily on lens design or Fourier optics, Boyd’s work addresses the quantitative measurement of optical radiation. The book is structured to lead the reader from the most fundamental definitions to the nuanced performance characteristics of real detectors. Boyd, a pioneer in nonlinear optics, reminds us
Part I: Foundations of Radiometry Boyd begins with the classical language of the field: radiant flux, intensity, radiance, and irradiance. He clarifies the often-confused distinctions between radiometric (power-based), photometric (eye-weighted), and quantum (photon-based) quantities. A key strength here is the treatment of etendue and throughput—concepts critical for designing optical systems that collect or deliver light efficiently.
Part II: Detector Physics The core of the text is a methodical exploration of optical detectors. Boyd classifies detectors into two main categories: Part III: Noise and Detection Limits Perhaps the
Part III: Noise and Detection Limits Perhaps the most valuable section for practicing scientists, this part covers the statistical fluctuations that limit measurement. Boyd systematically breaks down:
He derives the concept of Detectivity (D)* and shows how to compare detectors across different materials and sizes.
Part IV: Heterodyne Detection The final chapters introduce coherent detection—a technique where signal light is mixed with a local oscillator on a fast detector. Boyd explains why heterodyne detection can approach the quantum limit (the standard quantum limit for optical measurements) and its applications in lidar and spectroscopy.