## 1 Coherent Diffraction Imaging Using Synchrotron Light Source  
High-resolution structure determination of macromolecular and biological particles is an important tool for the life science and biological community [1; 2; 3; 4]. Apart from X-ray crystallography and spectroscopy, microscopy is the most widely used technique for structure determination in physical, material and biological sciences. Multiple imaging methods, such as optical microscopy (including general optical microscopy, laser confocal microscopy and super-resolution microscopy) [5; 6; 7; 8; 9], electron microscopy [10; 11; 12; 13] and X-ray microscopy [14; 15; 16] have been employed by researchers. Nevertheless, the resolution of an optical microscope is always limited by the wavelength of the radiation used (\(\sim\)200 nm for visible light). For super-resolution microscopy, the sample has to be labeled, which will limit the applications of photoactivated localization microscopy (PALM) [17], stochastic optical reconstruction microscopy (STROM) [18] and stimulated emission depletion (STED) [19]. For scanning electron microscopy (SEM), it can only provide surface information [20]. Regarding transmission electron microscopy (TEM) [21], the penetration ability of electrons is a critical issue. The sample thickness has to be less than 50 nm [22], otherwise contrast is reduced due to multiple scattering of the electrons. To obtain structural information below the surface for thick samples, the sample has to be sliced, introducing artifacts in the final images. Compared to electrons, X-rays have a larger penetration depth, making them an ideal probe for most applications in structure determination. However, the scattering cross-section of X-rays is smaller than that of electrons [23]. The scattering efficiency is worse than that of electrons. Actually, neither X-rays nor electrons can achieve atomic resolution due to the limitation of radiation damage [24]. Only when the X-ray or electron pulse is shorter than the atomic motion timescale, such as in the order of 10 fs, could the valid snapshot be captured [25]. Under the same conditions, X-rays are better for thick samples without slicing and electrons are better for weak scattering samples with cryogenic cooling. Classical X-ray imaging methods, such as transmission X-ray microscopy (TXM), scanning transmission X-ray microscopy (STXM) and X-ray fluorescence imaging are based on X-ray optics [26] which will limit the highest obtainable resolution. At the moment, the achievable resolution of focusing optics has broken the 10 nm barrier [27; 28]. For X-ray crystallography, the samples have to be crystallized typically to a certain minimum size to obtain high resolution [29]. In addition to crystal growth and phasing, radiation damage is an extra challenge, especially when radiation sensitive samples such membrane or metal containing proteins. In 1952, [PERSON] underlined in a half-page paper that by measuring the diffraction intensity between the Bragg peaks, the phase problem of non-crystalline samples might be resolved [30]. Since then, oversampling theory [31; 32] and different types of phase retrieval algorithms [33; 34; 35; 36; 37; 38; 39; 40; 41] have developed rapidly. In 1999, [PERSON] and colleagues performed the first successful coherent diffraction imaging experiment [42]. This newly developed coherent diffraction imaging method is a form of lensless microscopy rather than relying on X-ray optics. The theoretical resolution is only limited by the incident light wavelength and the maximum diffraction angle recorded by the detector. The past 18 years have witnessed a great success of coherent diffraction imaging, especially under the use of high flux X-ray light source facilities, such as advanced 3 rd generation synchrotron facility Super Photon ring-8 GeV (Spring-8, Hyogo, Japan), European Synchrotron Radiation Facility (ESRF, Grenoble, France) and Advanced Photon Source (APS, Lemont, IL, USA).