ISO 12233 slanted-edge method experiences errors using fast Fourier transform (FFT) in the camera modulation transfer function (MTF) measurement due to tilt angle errors in the knife-edge resulting in nonuniform sampling of the edge spread function (ESF). In order to resolve this problem, a modified slanted-edge method using nonuniform fast Fourier transform (NUFFT) for camera MTF measurement is proposed. Theoretical simulations for images with noise at a different nonuniform sampling rate of ESF are performed using the proposed modified slanted-edge method. It is shown that the proposed method successfully eliminates the error due to the nonuniform sampling of the ESF. An experimental setup for camera MTF measurement is established to verify the accuracy of the proposed method. The experiment results show that under different nonuniform sampling rates of ESF, the proposed modified slanted-edge method has improved accuracy for the camera MTF measurement compared to the ISO 12233 slanted-edge method.
We propose a new idea to measure the temporal contrast of laser pulses in this paper. Unlike the traditional time-to-space transformation method, the design in this paper can be called a somewhat time-to-time transformation. A single-shot pulse beam is simultaneously divided into two separate beams by a beam splitter. The two beams then enter a pair of optical replicators respectively to generate two pulse sequences that have equal time intervals respectively. The time interval of the two sequences alters by about 100fs that we can use one sequence to scan the other at a time resolution of 100fs through a nonlinear crystal. The time resolution depends on the altering of time interval and the time window depends on the pulse number of the sequence. This method can avoid the spatial modulation of the laser pulse. On the other side, the time resolution and time window are adjustable. It is also possible to measure the high contrast with a low-dynamic- range detector by attenuating the power of each pulse in the sequence respectively.