Development Of The Laser Intensity And Profile Measurement System Of IR-FEL

Free Electron Laser(FEL)has the advantages of continuously adjustable wavelength,wide spectral range,high laser power,and flexible pulse structure etc.,which are not available in conventional lasers.Therefore,free electron laser has broad application prospects in the fields of national defense,scientific research,industry,and medicine etc.Tunable Infrared Laser for Fundamentals of Energy Chemistry(FELiChEM)includes infrared free electron laser(IR-FEL)light source facility and three user experimental stations.The device is the first domestic infrared free electron laser user device built in University of Science and Technology of China.Its core components are two FEL oscillators that produce continuously adjustable wavelengths mid-infrared and far-infrared lasers with a spectral range of 2.5-200p.m.It is a specialized infrared source designed to conduct research in energy chemistry and other aspects.According to the design parameters such as laser power,wavelength and pulse structure of the infrared free electron laser facility,a system suitable for IR-FEL laser intensity and laser beam profile measurement is designed.Laser intensity and laser beam size are important basic parameters of FEL.The measurement of these two parameters can know the state of the device and provide an important basis for further commissioning and operation.By measuring the macro-pulse waveform of the FEL,not only the gain and cavity loss of the FEL facility can be evaluated,but also the laser power can be calculated to determine whether the light is saturated or not.By measuring the spot,the spatial distribution of the free electron laser can be known,while the focus of the laser and the spot size of the laser are known.The IR-FEL laser intensity and laser beam profile measurement system designed in this paper contains the following parts.For the measurement of laser intensity,pyroelectric detector and associated electronics are used to measure the macro-pulse waveform of the FEL.Commercial pyroelectric CCD camera for laser beam profile measurement.The design of the optical path mainly uses stepping motor combined with gold-plated mirror and off-axis parabolic mirror to realize the focus of FEL and time-division multiplexing of laser intensity and laser beam profile measurement.Pyroelectric CCD camera control software and stepper motor control software are programmed by LabVIEW.Since the infrared absorption of water in the air is serious,the shield of the acrylic material is designed so that the entire system is in dry air.In addition,the entire measurement system works in a strong radiation environment,and the lead box is designed to shield the electronic module and reduce the influence of radiation on the measurement results.The designed IRFEL light intensity measurement system was tested offline and online respectively.The test results show that the measurement system can measure the laser with a pulse width of 10?s,and the online test results are similar to the low temperature Ge:Ga detector in the CAEP THz-FEL facility.The Test results and simulation analysis show that the pyroelectric detector has adjustable voltage responsivity and bandwidth to meet different measurement and test requirements.It can be seen that the designed measuring system meets the measurement requirements of the IR-FEL facility.