Elementary analysis device by optical emission spectrometry on laser produced plasma

• US 20050024638A1
• Filed: 09/01/2004
• Published: 02/03/2005
• Est. Priority Date: 11/03/1999
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Inventors: Lacour, Jean-Luc, Wagner, Jean-Francois, Mauchien, Patrick, Detalle, Vincent
• Granted Patent: US 7,106,439 B2
• Time in Patent Office: Days
• US Class Current: 356/318
• CPC Class Codes: G01N 21/718 Laser microanalysis, i.e. with formation of sample plasma

Abstract

This device comprises a pulsed laser source (6), means (8, 10, 12) for focusing light from this source onto an object to be analysed (2) to produce plasma on the surface of the object, means (16, 18) of analysing a plasma radiation spectrum, means (20) of determining the elementary composition of the object from this analysis, and possibly means (4) for displacing the object. The invention is particularly applicable to test radioactive materials.

Claims

1. Elementary analysis device by optical emission spectrometry on laser produced plasma, this device being characterized in that it comprises:

a pulsed laser source (6)

a diaphragm (8) usable for selecting part of the laser beam emitted by the source, and possibly delimiting the shape of the impact of the laser beam on an object to be analysed (2), this laser beam not being focused in the plane of the diaphragm,

first optical means (10) capable of projecting the image of the diaphragm to infinity,

second optical means (12) designed to receive the image of the diaphragm projected to infinity by the first optical means and focusing it on the object to be analysed to produce plasma (28) on the surface of this object, the assembly formed by the diaphragm and the first and second optical means also satisfying the following conditions;

the image of the diaphragm focused on the object is equal to the required dimension on this object

the focal point of the laser beam, after crossing through the diaphragm and the first and second optical means, is outside the image plane of the diaphragm,

means (16, 18) of analysing a light radiation spectrum emitted by the plasma, and

means (20) of determining the elementary composition of the object starting from this spectrum analysis.

2. Device according to claim 1, in which the second optical means (12) have a digital aperture equal to approximately 0.1 or greater.

3. Device according to claim 1, in which the impact size of the laser beam on the object is greater than or equal to 1 μ

m.

4. Device according to claim 1, in which the displacement frequency of the object (2) between two laser pulses of the source (6) is greater than or equal to 15 Hz.

5. Device according to claim 1, in which the source (6) is capable of emitting ultraviolet light.

6. Device according to claim 1, in which the relative variation of energy between 1 laser pulse and the next does not exceed 5%.

7. Device according to claim 1, in which the diaphragm (8) comprises a circular aperture capable of selecting the central part of the laser beam output from the laser source, the first optical means are refractive optical means, and the second optical means are refractive optical means comprising a microscope objective (12).

8. Device according to claim 7, in which the first and second optical means (10, 12) are anti-reflection treated for reflections at the wavelength of the light emitted by the laser source (6).

9. Device according to claim 1, also comprising means (38) of blowing a gas jet onto the object (2).

10. Device according to claim 1, also comprising:

means (32) of observing the object, so that the object can be placed in the image plane of the diaphragm and

a mirror (26) reflecting at the wavelength of the laser source and transparent at other wavelengths, this mirror being placed on the light path between the first and second optical means and designed to reflect almost the entire laser beam to these second optical means and to transmit an image of the object to the observation means.