## 2 Coherent Diffraction Imaging with X-ray Lasers
The concept of “diffraction-before-destruction” was demonstrated at the limited resolution available; (**b**) Time-resolved diffractive imaging of a man-made sample. Laser-pump X-ray-probe was applied at different time delays. In this case, the sample is seen to get destroyed under the high pump laser intensity and the features are disappearing after 15 ps; (**c**) Bragg coherent diffraction imaging of gold nanoparticles with hard X-ray lasers was employed at the Linac Coherent Light Source (LCLS). For different time delays, the changes in the diffraction patterns can be used to image phonon dynamics; (**d**) Morphology and chemical components of aerosol particles were captured by coherent diffraction imaging combined with time-of-flight mass spectrometry at LCLS; (**e**) Three-dimensional imaging of nanoparticle from SACLA. By using the symmetry of gold nanoparticles, 48 diffraction patterns were generated. The 3D image was obtained after the finding of common arcs and phase retrieval. The resolution as determined by Fourier shell correlation (FSC) is \(\sim\)5.5 nm. (Figure 2a was reproduced with permission from [101]. Copyright Springer Nature, 2006. Figure 2b was reproduced with permission from [120]. Copyright Springer Nature, 2008. Figure 2c was reproduced with permission from [128]. Copyright The American Association for the Advancement of Science, 2013. Figure 2d was reproduced with permission from [126]. Copyright Springer Nature, 2012. Figure 2e was reproduced with permission from [131]. Copyright Springer Nature, 2014.). collections of separate cell images from individual cells and high-throughput imaging over populations of cells can sample unique occurrences. In this big data era, images from populations of genetically identical cells often reveal heterogeneous phenotypes, which can be helpful to group behavior research. Figure 3b [137] shows the high-throughput imaging of heterogeneous cell organelles with 120 Hz X-ray laser pulses from LCLS. Morphology and inner electron density were reconstructed by phase retrieval automatically. This result could pave the way for further biological functional imaging with XFEL. Figure 3c [136] demonstrates the combination of synchrotron XFEL together for one sample where one facility could not solve all challenges. This combined experiment illustrates the differences between facilities. Figure 3d [141] shows the successful demonstration of living cell imaging of cyanobacteria. Living cyanobacteria were injected into the X-ray beam using an aerosol injector. During the short delivery time from solution to the vacuum of the experimental chamber, the cyanobacteria remain in a living state and they were then imaged by coherent diffraction. This demonstrates the capability for the real structure determination of biological samples under near native state. Figure 3e shows the first 3D imaging of biological samples using an XFEL [139]. Hundreds of diffraction patterns with different SNR and random orientations were recorded. After hit finding, pattern classifications, orientation determination and phasing, a 3D real-space volume with a full-period resolution of 120 nm was generated. This demonstration paves the way for 3D single-particle imaging, with the ultimate goal of achieving atomic resolution requiring further effort. Figure 3: Coherent diffractive imaging of biological samples with X-ray free-electron lasers. (**a**) First coherent diffraction imaging of biological samples with hard X-ray lasers at LCLS. The sample, mimivirus, is one of the largest known viruses. The total diameter of the particle, including fibrils, is about 750 nm. The full-period resolution of this first demonstration is \(\sim\)32 nm; (**b**) High-throughput imaging of heterogeneous cell organelles. Around 70,000 low-noise diffraction patterns were collected within 12 min at LCLS at a frequency of 120 Hz.