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Laser Energy and Power Measurement
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Average power is calculated by measuring the PRR and multiplying by the pulse energy. Many manufacturers have systems that can measure pulsed lasers up to 25 kHz. Pyroelectric sensors use a ferroelectric crystal that has a permanent electrical polarization. Incident light heats the crystal, changing the dipole moment and causing current to flow. The current can charge a capacitor in parallel with the crystal to create a voltage proportional to the pulse energy and then the capacitor switched (short-circuited) to be ready for the next pulse. Because pyroelectrics respond only to change of temperature, the source must be pulsed or modulated. The response time of a pyroelectric sensor is much faster than a thermopile and can make a stable measurement within several hundred microseconds. Pyroelectric sensors work well with pulsed lasers with 100 nJ to >10 J pulses in the 0.15–12 μm wavelength range.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Pyroelectric sensors are made from pyroelectric materials, which are crystals capable of generating charge in response to heat flow. Pyroelectric sensors consist of thin slices or films with electrodes deposited on the opposite side to collect the thermally induced charges. The most common pyroelectric materials are lead zirconate titanate, triglycine sulphate, lithium tantalite, and polyvinyl fluoride. Most commercial pyroelectric sensors are made from single crystals, such as triglycine sulphate, PZT ceramics, or LiTaO3 The polyvinyl fluoride-based sensors exhibit high-speed responses and good lateral resolutions.
Laser Output Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
A pyroelectric probe uses a ferroelectric material that is electrically polarized at a certain temperature. The material is placed between two electrodes. Any change in temperature of the material caused by the absorption of laser power produces a response electric current in the external circuit. Pyroelectric probes are primarily used to measure the energy of pulsed lasers because they only respond to the rate of temperature change. Pyroelectric probes usually have a spectral response range from 100 nm to 100 μm, a response time as short as a few picoseconds, and a pulsed energy range from 10 nJ to 20 J.
Side-coupled nanoscale photonic crystal structure with high-Q and high-stability for simultaneous refractive index and temperature sensing
Published in Journal of Modern Optics, 2019
Zhiqiang Liu, Fujun Sun, Chao Wang, Huiping Tian
In the sensing field, the RI is one of the most important optical parameters for the materials because it offers an indication of several physical and chemical changes. Hence, the RI detection in the photonic crystal will have a wider range of applications in the future, and it is worth more research and exploration. Zhang et al. (11) proposed an optofluidic sensor based on silicon photonic crystal nanobeam cavities and the sensitivities are 58 and 139 nm/RIU, respectively. Nunes et al. (12) proposed a 1D photonic crystal in a microfluidic channel as a refractive index sensor which obtained a sensitivity of 836 nm/RIU. In addition to the RI of the surroundings, the ambient temperature is also a common parameter for sensing. Unlike the RI sensing, the effect of ambient temperature on photonic crystal sensing is the effect of RI changes of the photonic crystal material and the experimental environment simultaneously. Lu et al. (13) designed an enhanced nano-optical pyroelectric sensor which shows a sensitivity of 35.9 pm/K for temperature sensing. Zhang et al. (14) presented a high sensitivity temperature sensor based on cascaded silicon photonic crystal, and the experimental results show that the sensitivity of the temperature sensor is about 162.9 pm/K.
A strategy for optimal energy conversion by pyroelectricity
Published in International Journal of Green Energy, 2018
Chun-Ching Hsiao, An-Shen Siao, Yi-Je Tsai
Heat remains an almost ubiquitous and abundant ambient source of energy that is often wasted as low-grade waste heat. Low-grade waste heat is greatly generated as a by-product of power, refrigeration or heat pump cycles. Thermoelectric generators with thermoelectric materials have attracted interest as a means for harvesting waste heat; however, they require bulky heat sinks to convert temperature gradients into electrical energy using the Seebeck effect. Pyroelectric materials are of interest because they have the potential to operate with a high thermodynamic efficiency under correct conditions (Sebald, Lefeuvre, and Guyornar 2008). Pyroelectricity is a property whereby a charge is generated on the surface of pyroelectric material as a result of a change in temperature. It manifests itself in polar materials because of the temperature dependence of its electrical polarization. Pyroelectric materials produce power from temperature fluctuations (dT/dt), while thermoelectric systems generate electric power from temperature gradients (dT/dx). If a pyroelectric material is heated (dT/dt> 0), there is a decrease in its level of spontaneous polarization as dipoles within the material lose their orientation due to thermal vibrations. This leads to a decrease in the number of free charges bound to the material’s surface. In open circuit situations, the free charges remain on the electrode’s surface, and an electric potential is produced across the material. In short circuit situations, electric current flows between the two polar surfaces of the material. Furthermore, if the pyroelectric material is cooled (dT/dt< 0), the dipoles regain their orientation for further inducing to increase the level of spontaneous polarization. The electric current flow is reversed under short circuit situations, and free charges are attracted to the polar surfaces. The generated charges yield a voltage across the pyroelectric material before they are released by an external circuit or internal resistance (Sharma et al. 2015). In addition, the microstructure of the pyroelectric materials (such as grain size and porosity) plays a vital role in the pyroelectric response, thermal conductivity and specific heat for further influencing the efficiency in pyroelectric harvesters (Jiang et al. 2015; Zhang et al. 2011a, 2009, 2009b). Although the pyroelectric effect can be used to thermal energy harvesting (Bowen et al. 2014; Yu et al. 2015; Zhang et al. 2018), lead-system materials such as PZT with a high pyroelectric coefficient are widely adopted to enhance the energy conversion efficiency (Zeng et al. 2013; Zhang et al. 2009). Namely, lead may enter the environment from the manufacture of the high lead content materials.