In this paper, a series of experiments on dispersion compensation in terahertz time-domain spectrometers are performed. The Influence of femtosecond laser pulse width on the performance of terahertz time-domain spectrometers is systematically studied. A terahertz time-domain spectroscopy system was constructed using fiber-coupled photoconductive antennas. Through the adjustment of the grating spacing and the replacement of different lengths of fiber cable, the laser pulse width acting on the antenna was multiplexed from 130fs to 2.46ps, and the performance of the terahertz time domain spectroscopy system under different pulse widths was tested. The experimental results show that, with the increase of the femtosecond laser pulse width, the signal intensity of the terahertz time domain waveform and the high frequency part of the terahertz spectrum decrease significantly. Quantitative comparative analysis was performed using the average signal-to-noise ratio, validating the necessity of using dispersion compensation and femtosecond laser pulse width testing in the terahertz time-domain spectroscopy system.
The infrared small spot system is the main equipment to test the crosstalk of the infrared focal plane array device. According to the current test method can’t meet the infrared light spot characteristics of the test problem, the use of infrared imaging device scanning technology to build a small infrared light beam characteristics of the calibration System, to achieve the infrared light spot characteristics of the measurement, and the system of the uncertainty was assessed. Finally, chooses an infrared small spot optical system is used to verify the measurement uncertainty of the system. It can be seen from the data analysis that the method can measure the characteristics of the infrared light beam and meet the measurement of the infrared small spot optical system. Infrared small spot system development and infrared focal plane crosstalk test to play a certain help.
Spectral response is one of the important technological parameters of the detector, along with the development of the ultraviolet detector technology, accurate measurement of UV detector spectral responsivity is becoming more and more important. This paper analyzes the ultraviolet focal plane array relative spectral responsivity measurement principle, using the substitution method of measuring ultraviolet focal plane array detector relative spectral responsivity, and established a calibration device for relative spectral response of UV focal plane array. The relative spectral response of UV focal plane array device was obtained,can be seen from the curves, UV focal plane array device from 250 nm to 290 nm spectral response range, the peak response near 270 nm, Show that the array sun-blind characteristic of a device. The uncertainty of analysis results showed that UV focal plane array device relative spectral response measurement uncertainty of calibration device is about 3.6%, can meet the demand of high precision measurement.
Terahertz technology is getting fast development in scientific research and the characteristics of terahertz beam is of great importance when using a terahertz laser. In this paper we scan the THz beam along its diameter by a slit and a circular aperture to measure the THz beam’s power distribution and thus get its spot’s size. The results show that the beam spot of the THz source we employed is satisfied with Gaussian distribution. The value of the peak power would affect the determination of the spot boundary, the influence of environmental noise will increases when the the peak power become weak and the measured spot diameter will be too large ultimately.
Terahertz metrology is becoming more and more important along with the fast development of terahertz technology. This paper reviews the research works of the groups from the physikalisch-technische bundesanstalt (PTB), National institute of standards and technology (NIST), National physical laboratory (NPL), National institute of metrology (NIM) and some other research institutes. The contents mainly focus on the metrology of parameters of power, frequency, spectrum and pulse. At the end of the paper, the prospect of terahertz metrology is predicted.
Modulation transfer function (MTF) is one of the most important parameters of infrared focal plane array (IRFPA). A double-knife edge scanning method is proposed for MTF measurement of IRFPA. In this method, a double-knife edge was used as a target, and the IRFPA under test was positioned in the focal plane of the imaging optical system by a 3-axis translation stage. With an IRFPA data acquisition system, the image of the double-knife edge was restored. By scanning in the direction orthogonal to the double-knife edge image, edge spread function (ESF) curve of each pixel swept across the knife-edge image was obtained. MTF could be calculated from the subsequent fitting, differential and Fourier transformation procedures. With double-knife edge scanning, two ESF curves of double-knife edge were obtained simultaneously, and symmetry of the two ESF curves could be used to evaluate the verticality between photosensitive surface of IRFPA and optical axis of the double-knife edge imaging system. In addition, this method can be used to judge the existing of interference from outside such as vibration, stray light and electrical noise. A measurement facility for IRFPA’s MTF based on double-knife edge scanning method was also established in this study. The facility is composed of double-knife edge imaging optical system, 3-axis translation stage and data acquisition system, et al. As the kernel of the facility, the double-knife edge imaging optical system mainly comprises two symmetrical parabolic mirrors coating with reflective material, and the magnification of the optical system is 1 with an operation wavelength range of (1∼14) μm.
The method of knife-edge scanning is always adopted in testing the MTF of infrared focal plane array (IRFPA), and
accurate focusing is one of the most important preconditions in the measurement procedure, because the measurement
accuracy of MTF is ensured only when IRFPA is placed in the focal plane of the knife-edge imaging optical system. In
this paper, a focusing method based on the area value under normalized MTF curve is proposed. Firstly, we analyzed
MTF calculation model, which contained derivation of edge spread function (ESF) and then Fourier transformation. In
this way, the issue of larger area under normalized MTF curve meant better focusing degree of the measurement system
was proved. Next, the quasi-focal plane position of knife-edge optical system was determined according to the output
voltage values of pixels of IRFPA. Then a series of MTF curves were measured when IRFPA was placed at different
positions located in the optical axis beside the determined quasi-focal plane at an increment of 60 μm. Subsequently, the
area under each normalized MTF curve was calculated, and the result showed the area values presented a perfect
Lorentzian distribution against the positions of IRFPA. It was concluded the peak position of the fitted Lorentzian curve
corresponded to the position of focal plane of knife-edge optical system. With this method, the focal plane position of
knife-edge optical system was determined. The method presented here can be used to focus the MTF testing system with
a high accuracy, which is good for the following MTF measurement.