Hi,

The standard method in this case is to use Intensified CCD cameras, which gate time can be as short as a few nanosecond, more than enough in the case of nanoparticles. You can generally then observe the cloud of nanoparticles expanding thanks to blackbody radiation. Additionnally, you can couple ICCD with Emission Spectroscopy to determine some properties of the nanoparticles (such as temperature, with good care…). You will lose one dimension though.

For nanoparticles sizing, it's quite a complicated problem. I tried such things in the case of laser ablation in vacuum, using extinction spectroscopy. The results are in one of my papers.

I wish you good luck!

Additionnally, 

You try to use a magnetic field, maybe the particles is retarded.

You can try the following: make a laser lightsheet with a cylindrical lense through which the particles have to pass. Use a camera that is a fast as possible and try to photograph the passing particles - they should make a kind of light "streak" on the pictures - when you know the shutter time of your camera and the length of the streaks, you can easily calculate the velocity of the particles (if you can make pictures from different directions simultaniously, you see also the direction of the particles).

Hi,

The standard method in this case is to use Intensified CCD cameras, which gate time can be as short as a few nanosecond, more than enough in the case of nanoparticles. You can generally then observe the cloud of nanoparticles expanding thanks to blackbody radiation. Additionnally, you can couple ICCD with Emission Spectroscopy to determine some properties of the nanoparticles (such as temperature, with good care…). You will lose one dimension though.

For nanoparticles sizing, it's quite a complicated problem. I tried such things in the case of laser ablation in vacuum, using extinction spectroscopy. The results are in one of my papers.

I wish you good luck!

Additionnally, 

@Florent Bourquard

I notice that your work were focusing on the nanoparticles. however, for some plastic material like glass, particles with size of ~um will be prominent in the >10us delay after the pump pulse. so, what are those great ideas to investigate them?

@Chao:

I'm not so familiar with the specifics of glass ablation, but aren't those microparticles hot enough to produce blackbody radiation ? In this case, you could characterize their position via ICCD direct imaging. As long as they're emitting, you can see them.

During my research, I found this paper summarizing optical characterization of NPs in situ http://onlinelibrary.wiley.com/doi/10.1002/ctpp.201000056/abstract . That's not specifically for laser ablation, and focuses on NPs: so it's up to you to check which technique you can adapt to your micro particles.

Velocity and size of droplets can be determined by scattering or absorption and using as was mentioned above ICCD with chosen gate delay and width (may be 4 channel PCO CCD http://www.pco.de or multiple fibers). But it seems to me that droplet (particle) size should be ~ critical bubble radius (glass melts, boils, so bubble are grown and on the surface are exploded). Therefore it is possible to estimate mass, energy and velocity of droplets.

You can use a system for high velocity like this:

https://www.youtube.com/watch?v=BicVttrrxI0

You have a description here:

https://pure.ltu.se/portal/files/42972834/Ingemar_Eriksson_Komplett.pdf

We are thinking about buying a system like this:

http://www.oxfordlasers.com/imaging/

Hi

There are many methods to do what you want. Optical methods, spectroscopic methods, Langmuir probes, CCDs  to detect the angular distribution, mass spectrometry methods etcetera. Each of them has its advantages and disadvantages.

One thing that has to taken into account is the duration of the laser pulse used. If it is not femtoseconds then you would have to deal with the interaction between the laser radiation and the ejected particles. in any case the ejected particles create a cloud of relatively dense plasma called the plume. In the first phases of the plume -the more dense ones- the information about dynamic parameters is lost due to the collisions in the plasma.

For the purpose of investigating the ejecta I particularly  like the Time of flight mass spectrometer equipped with Delayed Extraction. The reason for the presence of the Delayed Extraction is that by having a delay before the extraction voltage is applied the plasma plume is allowed to expand without the influence of the external electric field. this results in avoiding increasing  the speeds of the particles and the collision rates in the plume. Your picture of the plume will be more accurate. I have a couple of papers in the subject which I am attaching.

Another tool that I would recommend is a position sensitive detector named ionCCD. It is a 1D array CCD that can detect ions regardless their kinetic energy. All the particle needs is to have charge to be detected. It could be used to measure the angular distribution of the ejected ions. One of the advantages of this detector is that it can be used in vacuum as well as at atmospheric pressure. In attachment there is an example of how I used it.

One method that I like as well is to tag the analyte of interest with a fluorescent compound and observe the evolution of the plume by detecting the fluorescence  with a suitable fast camera. Look for the pares of Geohegan at

http://web.ornl.gov/~odg/publications.html

Finally regarding the measurement of size. You could try to use the forward scattered light of a suitable wavelength (lets say 488 nm). Perhaps you would have to conform the particles in a beam that could be measured this way. Take a look of what is done in flow cytometry.

Please find: Optics and Lasers in Engineering

Volume 50, Issue 5, May 2012, Pages 717-726

Influence of the interaction between nanoparticles and high brilliant laser radiation during μs-pulses on the ablation process of metals 

Scholz, T. , Dickmann, K, Uphoff, H., Lammers, L 

This method (light scattering) is good for nm and um size particles

你可以看看这篇文献，是介绍熔石英损伤的。

Material response during nanosecond laser induced breakdown inside of the exit surface of fused silica 

http://onlinelibrary.wiley.com/doi/10.1002/lpor.201200100/full

Please have a look on this paper. 

Applied Physics A

January 2010, Volume 98, Issue 1, pp 153-159

Diagnostics and expansion dynamics of the plume produced by laser ablation of a LiYF4 crystal in vacuum

A. Bogi, S. Barsanti, M. Anwar-Ul-Haq, P. Bicchi

If you think about charged particles, you may use Faraday cups to resolve velocity and angular distribution at a given distance from the target.

If the particle size is large enough, you can use a laser with the light scattering to detect them. This technique can be coupled with a mass spectrometer or a Faraday cup to characterize completely the particulate in laser ablation. 

The particles can be also deposited on a substrate, that can be analyzed by a microscope. Measuring the velocity however is very complex. 

I think that these particles are transported by the plume, therefore also a measure of the plume speed by a time-of-flight analysis can be useful.