|
Abstract:
|
Accurate single -shot visualization of laser wakefield structures can improve our fundamental understanding of plasma -based accelerators . Previously , frequency domain holography (FDH ) was used to visualize weakly nonlinear sinusoidal wakes in plasmas of density n[subscript e] < 0 .6 × 10¹⁹ /cm³ that produced few or no relativistic electrons . Here , I address the more challenging task of visualizing highly nonlinear wakes in plasmas of density n[subscript e] ~ 1 to 3× 10¹⁹ /cm³ that can produce high -quality relativistic electron beams . Nonlinear wakes were driven by 30 TW , 30 fs , 800 nm pump pulses . When bubbles formed , part of a 400 nm , co -propagating , overlapping probe pulse became trapped inside them , creating a light packet of plasma wavelength dimensions - -that is , an optical "bullet" - -that I reconstruct by FDH methods . As ne increased , the bullets first appeared at 0 .8 × 10¹⁹ /cm³ , the first observation of bubble formation below the electron capture threshold . WAKE simulations confirmed bubble formation without electron capture and the trapping of optical bullets at this density . At n[subscript] >1× 10¹⁹ /cm³ , bullets appeared with high shot -to -shot stability together with quasi -monoenergetic relativistic electrons . I also directly observed the temporal walk -off of the optical bullet from the beam -loaded plasma bubble revealed by FDH phase shift data , providing unprecedented visualization of the electron injection and beam loading processes . There are five chapters in this thesis . Chapter 1 introduces general laser plasma - based accelerators (LPA ) . Chapter 2 discusses the FDH imaging technique , including the setup and reconstruction process . In 2006 , Dr . N . H . Matlis used FDH to image a linear plasma wakefield . His work is also presented in Chapter 2 but with new analyses . Chapter 3 , the main part of the thesis , discusses the visualization of LPAs in the bubble regime . Chapter 4 presents the concept of frequency domain tomography . Chapter 5 suggests future directions for research in FDH . |