The Rayleigh scattering method is widely adopted in measuring cluster size.In general,it is considered that the intensity of scattering corresponds to the cluster size directly.However,this paper deduces that the intensity is not only related to cluster size,but also to gas density and binding probability.It suggests that gas density should be taken into account in analyzing the measurement results of Rayleigh scattering method.Furthermore,the method is applied in measuring the size distribution of argon cluster along the axis of nozzle.It is found that the cluster size doesn't vary linearly along the nozzle axis,whereas it reaches maximum at a certain position which depends on some parameters including the background pressure.

Large deuterium clusters were produced in a supersonic expansion of high pressure gases into vacuum through a 0.5 mm nozzle.The average size clusters(with 3×103 atoms) was verified by measuring the Rayleigh scattered signal using a He-Ne laser beam.Neutrons(2.45 MeV) from deuterium clusters fusion induced by the intense femtosecond(30 fs) laser pulse is experimentally demonstrated.The average neutron yield of 1×103 per shot was obtained.The yield grew slightly with the increasing of the laser spot size.No neutron was observed when the laser spot was larger than 470 micron.The fusion events mainly happened in the hot plasma region radiated by the intense laser.

We have developed and carried out a detailed characterization of a cryogenically cooled (80 K) high-pressure (50 x 10(5) Pa) solenoid driven pulsed valve that has been used to produce dense jets of deuterium atomic clusters for interaction studies with high intensity laser. Rayleigh scattering was employed to investigate the scaling law between cluster size and upstream gas pressure, which was shown to be of the form N-c proportional to P-0(2.89). Cluster size gets to its peak N-c approximate to 2630 at 80 K, 48 x 10(5) Pa. We also studied the cluster formation process, portrayed a characteristic curve which revealed cluster size temporal evolution. Our results are important for analyzing the cluster interaction with intense laser, and are expected to provide guidelines to choose proper fire time.

Neutrons (2.45 MeV) from deuterium cluster fusion induced by the intense femtosecond (30 fs) laser pulse are experimentally demonstrated. The average neutron yield 103 per shot is obtained. It is found that the yield slightly increases with the increasing laser spot size. No neutron can be observed when the laser intensity I < 4.3×1015 W/cm2.

A one-dimensional model was constructed to calculate the gas density profile within a few millimeters of the conical nozzle. The result from the model is in agreement with experiments. A program was developed to deal with data taken by the M-Z interferometry, which measures the two-dimensional spatial distribution of the gas density profile in front of the conical nozzle. In the interaction experiment, we can choose a proper backing pressure to achieve expectant density, according to the scaling of density with backing pressure. And the scaling of density with relative delay time was expected to provide instructions in establishing the relative timing between firing the jet and the arrival of the laser pulse in interaction experiments.

The Rayleigh scattering and Mach-Zehnder interferometry are employed to investigate the properties of argon and krypton clusters respectively.By comparing the size and density of the two kinds of clusters in detail,the factors of cluster formation are discussed.Varying the delay time between probe laser and nozzle valve,the temporal evolution of size and density is obtained,the density spatial distribution along nozzle axis with the background pressure from 1.2 MPa to 6.0 MPa is measured.Both size and density of the argon and krypton clusters reach max and the system is stable from 3 ms to 25 ms.In addition,the density increases linearly with background pressure,and decreases with the distance away from the nozzle throat.

High-energy ion emission from intense-ultrashort (30fs) laser-pulse- cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweiback's expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.