Measuring laser power and pulse energy

Although it is not necessarily of primary importance in laser chemistry experiments to know the laser power or pulse energy exactly, relative consistency over time is nearly always an issue. Therefore, a means for measuring the power/energy content in a laser beam is required. 

alternative detection methods are often needed if high power or high pulse energy laser 

Thermal detectors measure the temperature difference generated within the detector by the heating from the laser radiation. Modem commercial devices consist of a metal disk, connected to a heat sink at its edge, and an array of thermocouples located across the disk such detectors are known as thermopiles. The thermocouples are connected in series to produce a voltage proportional to the temperature difference from the disk centre to the edge. 

When the incident laser power changes, a new thermal equilibrium condition evolves. This is a relatively slow process, and the response time of a typical thermopile is of the order of 1 s before the meter reading has stabilized. Clearly, this constimtes a disadvantage when rapid changes in laser beam power are important to monitor. On the other hand, thermal sensors are very versatile and robust. They work over an extremely broad spectral range, offer very uniform spatial response, and respond linearly to a wide range of input powers. 

Pyroelectric materials are non-conducting materials whose electrical polarization is a function of the 

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