Li Hua Yu

Coherent hard X-ray production by cascading stages of High Gain Harmonic Generation

Abstract We study a new approach to produce coherent hard X-rays by cascading several stages of High Gain Harmonic Generation (HGHG). Our calculation shows that such a scheme is feasible within the present technology. Compared with the Self-Amplified Spontaneous Emission (SASE) scheme for the Linac Coherent Light Source (LCLS), the HGHG scheme can provide radiation with full longitudinal coherence, narrower bandwidth, more stable central wavelength, more controllable pulse length, and much higher performance stability. The electron bunch parameters used in our calculation are those of the DESY TTF and SLAC LCLS projects. To achieve similar output power, i.e. about 15 GW , the total length of the HGHG scheme will be 88 m , while that of SASE scheme will be around 100 m .

Theory of high gain harmonic generation: an analytical estimate

We discuss the theory of the High Gain Harmonic Generation (HGHG). First, we describe an analytical estimate using the HGHG parameters in the DUVFEL project at BNL as an example. We show that the effective energy spread in a chicane dispersion section is found to be very small, and the effect of finite emittance can be neglected during the calculation of coherent harmonic generation. Then we discuss some issues such as the intensity stability, and how to use HGHG to obtain information about local energy spread. We compare these issues with recent experimental results in the infrared. We discuss some of the key issues in the cascading HGHG scheme and its possible limitations.

ANALYTICAL THEORY OF INTENSITY FLUCTUATIONS IN SASE

Abstract Recent advances in SASE experiments stimulate interest in quantitative comparison of measurements with theory. Extending our previous analysis (Krinsky and Yu, Phys. Rev. A 35 (8) (1987) 3406) of the SASE intensity in guided modes, we provide an analytical description of the intensity fluctuations by calculating intensity correlation functions in the frequency domain. Comparison of our results with experiment yields new insight into the SASE process.

Photoinjected energy recovery linac upgrade for the National Synchrotron Light Source

We describe a major paradygm shift in in the approach to the production of synchrotron radiation This change will considerably improve the scientific capabilities of synchrotron light sources. We introduce plans for an upgrade of the National Synchrotron Light Source (NSLS). This upgrade will be based on the Photoinjected Energy Recovering Linac (PERL). This machine emerges from the union of two technologies, the laser-photocathode RF gun (photoinjector) and superconducting linear accelerators with beam energy recovery (Energy Recovering Linac). The upgrade will bring the NSLS users many new insertion device beam lines, brightness greater than 3rd generation light-sources and ultra-short pulse capabilities, not possible with storage ring light sources.

Eigenmodes and mode competition in a high-gain free-electron laser including alternating-gradient focusing

Abstract We solve the eigenvalue problem for a high gain free-electron laser in the “water-bag” model including alternating-gradient focusing by a variational-solution-based (VSB) expansion method. Such VSB expansion method is very efficient for finding the eigenvalue. The results agree with those obtained by numerical simulation quite well. We further discuss the mode degeneracy and mode competition.

Simulations for the FERMI@ELETTRA proposal to generate 40- and 10-nm coherent radiation using the HGHG scheme

We present the results of simulations for a free-electron laser system designed and based on upgraded parameters for the 1.0-GeV LINAC, that in its present form is located at the third-generation synchrotron radiation facility ELETTRA in Trieste, Italy. The calculation is carried out for two of the three beam lines of the project. For the first beam line, the system is based on the HGHG scheme to generate 40-nm coherent radiation by a 200-nm seed laser. For the second beam line we consider cascading the HGHG scheme twice to generate 10-nm radiation.

BNL Source Development Laboratory

The NSLS has a long-standing interest in providing the best possible synchrotron radiation sources for its user community, and hence, has recently established the Source Development Laboratory (SDL) to pursue research into fourth generation synchrotron radiation sources. A major element of the program includes development of a high peak power FEL meant to operate in the vacuum ultraviolet. The objective of the program is to develop the source, and experimental technology together to provide the greatest impact on UV science. The accelerator under construction for the SDL consists of a high brightness rf photocathode electron gun followed by a 230 MeV short pulse linac incorporating a magnetic chicane for pulse compression. The gun drive laser is a wide bandwidth Ti:sapphire regenerative amplifier capable of pulse shaping which will be used to study non-linear emittance compensation. Using the compressor, 1 nC bunches with a length as small as 50 micrometer sigma (2 kA peak current) are available for experiments. In this paper we briefly describe the facility and detail our plans for utilizing the 10 m long NISUS wiggler to carry out single pass FEL experiments. These include a 1 micrometer SASE demonstration, a seeded beam demonstration at 300 nm, and a high gain harmonic generation experiment at 200 nm. The application of chirped pulse amplification to this type of FEL also is discussed.

Femtosecond deep UV pulse by high gain harmonic generation from a chirped seed

Abstract In this work we show that the techniques of high gain harmonic generation and chirped pulse amplification (CPA) can be combined to generate deep-uv radiation with peak power of order of 100 GW and pulse width of 5 fs. The resulting pulse would have wide range of applications.

POWER SPECTRUM CALCULATION FOR THE CORNELL WIGGLER A SASE EXPERIMENT AT BNL

Abstract Recently, we showed (Yu, Phys. Rev. E 58 (1998) 4991) that the widely used simulation code TDA3D, even though a single-frequency code, can be used to determine the power spectrum in the SASE process with excellent approximation in the exponential growth regime. In this paper, we apply this method to the BNL Cornell Wiggler A SASE experiment as an example. When the gain is not very high, there are many modes in the radiation, which seems to make the analytical calculation very difficult. However, we show that the increment of the radiation due to SASE over the spontaneous radiation can be expanded in terms of guided modes with rapid convergence. Thus when the spontaneous radiation is subtracted from the SASE power during the calculation, there is a good agreement between the analytical theory and the numerical simulation.