Detection of Optical Signals

Antoni Rogalski, Zbigniew Bielecki

• Editore: CRC Press
• Anno: 2022
• ISBN:
  9781000543551
• Edizione: 1
• Argomento: Sciences physiques
• Categoria: Optique et lumière

Detection of Optical Signals provides a comprehensive overview of important technologies for photon detection, from the X-ray through ultraviolet, visible, infrared to far-infrared spectral regions. It uniquely combines perspectives from many disciplines, particularly within physics and electronics, which are necessary to have a complete understanding of optical receivers.

This interdisciplinary textbook aims to:

• Guide readers into more detailed and technical treatments of readout optical signals
• Give a broad overview of optical signal detection including terahertz region and two-dimensional material
• Help readers further their studies by offering chapter-end problems and recommended reading.

This is an invaluable resource for graduate students in physics and engineering, as well as a helpful refresher for those already working with aerospace sensors and systems, remote sensing, thermal imaging, military imaging, optical telecommunications, infrared spectroscopy, and light detection.

1Radiometry and Photometry

DOI: 10.1201/9781003263098-1

In this chapter we will introduce definitions and parameters characterising electromagnetic radiation. In practice, the term radiometry is usually limited to the measurement of infrared, visible and ultraviolet light using optical instruments. The radiometric calculations are an essential part in the characterisation of detectors and in determining the signal-to-noise ratio. Radiometry not only means detecting and measuring the energy of electromagnetic radiation, but it is also used to determine the power of radiation transferred from one object to another.

The term radiometry has a meaning similar to photometry, related to the visible range of radiation, where the notion of radiation photons is used. Photometry is the measurement of light, which is defined as radiation detectable by the human eye. It is restricted to the visible region, and all quantities are weighted by the spectral response of the eye. It is a quantitative science based on a statistical model of the human visual response to light – that is, our perception of light – under carefully controlled conditions.

Radiometry deals with radiant energy of any wavelength. Photometry is restricted to radiation in the visible region of spectrum. The basic unit of power in radiometry is the watt (W). Typical photometric units include lumen (luminous flux), candela (luminous intensity), lux (illuminance), and candela per square meter (luminance). The lumen is simply radiant power modified by the relative spectral sensitivity of the eye.

In this chapter we will review the radiometric measurements that form the basis of the detector performance analysis. We are not able to design a correct construction of devices without specifying the spectrum and the value of the radiation power emitted by the object (target) and falling on the detector. We will try to answer the basic question: what energy value is collected and transferred to the detector surface if we know the geometric configuration of the radiation source, detector and system optics? The answer to this question makes it possible to clearly determine the signal-to-noise ratio of the system.

In order to simplify our theoretical considerations, we will limit ourselves to non-coherent sources, which are perfectly black bodies. We will exclude lasers and other sources that are partially or completely coherent. Then, the calculation of the energy distribution on the surface is the result of a simple scalar summation and not the result of a vector sum of amplitudes, as in the case of a coherent interference. In addition, we ignore the influence of diffraction effects and assume the approximation of small angles (this is a significant limitation, as it does not include cases where the object is close to the measuring equipment). Under such conditions, the sine of a given angle can be approximated by the value of the angle expressed in radians.

This chapter provides some guidance in radiometry. For further details, see References [1–8].

1.1 Introduction

Electromagnetic radiation is divided into sub-bands depending on the wavelength: gamma radiation, X, ultraviolet, visible, infrared, microwave and radio waves. This division is determined by the nature of the sources...