Preface

Since the birth of light microscopy, various imaging and spectroscopic techniques, including electron microscopy, X-ray imaging, and absorption/emission spectroscopy, have been developed. The technologies have played an important role in physics, chemistry, and life science. Electron microscopy and X-ray imaging have been applied to directly observe three-dimensional (3D) material structures at atomic scales. Spectroscopies have been used to detect, identify, and quantify information on atoms and molecules. Research using imaging and spectroscopic techniques have brought abundant information on material culture to mankind. Many significant physics and chemical laws have been constructed through measurements of how materials respond in these experiments, but to truly understand what is going on, more sophisticated apparatus would be needed.

The material properties or dynamic phenomena we observe on macroscopic scales result from the countless interactions that take place between individual atoms on timescales as fast as a picosecond or femtosecond. For example, the OH stretch of water has a period of 10 femtoseconds. The motions involved are less than 0.1 angstrom. To study the processes on such intricate scales, time-resolved spectroscopies using femtosecond-pulsed lasers were proposed in the 20th century. At the beginning of the 21st century, ultrafast imaging spectroscopy with ultrashortpulsed electrons and X-rays were adapted using real-time and real-space imaging of dynamical processes in matter. Many transient phenomena were revealed, including dynamics of photodissociation and chemical reactions, photon-induced lattice heating and melting on picosecond time scales, other structural phase transitions, etc. The recent developments have opened the femtosecond time domain to atomically resolved dynamics.

Medical imaging is an indispensable imaging technology in our life. It is undergoing a revolution from analog imaging to digital imaging and has shifted from general X-ray radiographs to new modalities such as computerized tomography (CT), magnetic resonance imaging (MRI), and isotope imaging. CT, which combines the power of computer processing with X-ray imaging, provides high-resolution images of the bony structures in three different planes. MRI acquires images of internal body structures and becomes the imaging modality of choice for soft tissues and vascular structures. Isotope imaging is applied in the elucidation of hidden causes of pain such as tumors or cancers.

In this book, we introduce several novel imaging and spectroscope techniques and their applications concerning such subjects:


Although this book includes a limited number of topics, I think that the content in each chapter will be impressive to the reader. I hope this book will contribute to future developments and applications.

Finally, I am grateful to all authors for their contributions to this book and their efforts to complete the chapters. I also acknowledge the IntechOpen publishing team, especially Mateo Pulko for cooperation in the publishing process.

> **Dr. Jinfeng Yang** The Institute of Scientific and Industrial Research, Osaka University, Japan

> > **1**

imaging.

the samples must be pumped 107

**Chapter 1**

**1. Introduction**

*Jinfeng Yang and Hidehiro Yasuda*

because of the limitation of the speed of video camera.

Introductory Chapter: 4D Imaging

The study of ultrafast phenomena, including structural dynamics and molecular reactions, is of great interest for physics, chemistry, biology, and materials science. There are numerous examples of phase transitions in condensed materials and chemical reactions in free molecules proceeding on nanosecond, picosecond, and even femtosecond time scales. To study processes or reactions on such intricate scales, more sophisticated apparatus would be needed. It is well known that electron microscopy is a powerful imaging technique and is applied to a wide research field. The progress of electron microscopy has shown that three-dimensional (3D) material structures can be observed with an atomic spatial resolution. However, the conventional electron microscopy does not allow studying ultrafast processes

The study of ultrafast structural dynamics or molecular reactions requires the use of probes ensuring not only high spatial but also high temporal resolutions. For this purpose, the new development of ultrafast electron microscopy (UEM), by combining temporal resolution into conventional electron microscopy, has been begun in the world. UEM uses a short pulsed electron beam replacing the continuous electron beam in the conventional electron microscopy to image the atomic motion by time-resolved recording in real time. By introducing temporal resolution into 3D electron microscopy, UEM allows us to observe the four fundamental dimension structures of matter: three spatial and one temporal, which is called 4D

Recent developments in UEM have shown that spatial and temporal information of matter can be obtained simultaneously on very small and fast scales. The first UEM was proposed to observe fast processes using a modified 120-keV electron microscope by Ahmed H. Zewail, Nobel Prize winner in Chemistry 1999, in the California Institute of Technology [1, 2]. He and his colleagues succeeded to observe the laser-photon-induced picosecond structural phase transition in vanadium dioxide film using a stroboscopic method with "single" electron pulses [3]. Later, a hybrid 200-keV apparatus was developed. A spatial-temporal resolution of 3.4 Å and 250 fs has been achieved. Recently, there are many research activities focused on improving the electron source and electron optics inside the microscope to achieve better temporal and spatial resolutions [4–9]. However, in the current UEM,

ied must be perfectly reversible. To study the irreversible processes, it is necessary

In this chapter, we introduce a novel UEM method with relativistic-energy electron pulses. In this relativistic UEM, an advanced radio-frequency (rf) acceleration technology is used to generate relativistic femtosecond electron pulses containing a large number of electrons in pulse and to achieve single-shot femtosecond imaging

to record images with a larger number of electrons per pulse possible.

for the study of ultrafast irreversible structural processes.

times or more by the laser. The process being stud-

## **Chapter 1**
