HANDHELD LIBS DEVICE WITH ATMOSPHERIC PURGE

A handheld LIES device includes a laser source for generating a laser beam, a spectrometer subsystem for analyzing a plasma generated when the laser beam strikes a sample, and a nose section including an end plate with an aperture for the laser beam and for receiving plasma radiation and an optic spaced from the end plate defining with the end plate a cavity therebetween. An atmospheric purge subsystem includes an air pump with an intake exposed to the atmosphere and a conduit connected to the air pump providing an atmospheric gas mixture to the nose section cavity to purge the cavity of contaminants and keep the optic clean as the atmospheric gas mixture exits the cavity through the end plate aperture.

FIELD OF THE INVENTION

This subject invention relates to laser induced breakdown spectroscopy (LIBS) devices.

BACKGROUND OF THE INVENTION

LIBS devices are known and used to detect elemental concentration of many elements with some accuracy. These devices typically include a laser that sufficiently heats a portion of a sample to produce a plasma. Photons are emitted at wavelengths unique to the specific elements comprising the sample. A spectrometer subsystem detects the photons and is able to analyze which elements are present in the sample and at what concentration.

Argon is often used to purge the LIBS plasma region to enhance signal which results from its reduced thermal conductivity relative to air. Typically, the flow rate is high and the area purged is large. The gas may be used to purge a sample chamber in some prior art LIBS analysis systems. Accordingly, a large source (e.g., a tank) of argon gas may be required and must be towed along in the field. See U.S. Pat. Nos. 9,395,243; 6,700,660; 7,916,834; 10,718,716; 7,821,634; and 10,677,733 all incorporated herein by this reference.

For some handheld LIBS devices, argon or other inert gas purge subsystems are often used with small gas canisters and a regulator fluidly connected to the argon canister and providing argon gas to the plasma site. See, for example, U.S. Pat. No. 10,883,921 and published U.S. Application No. 2008/0192897, both incorporated herein by this reference.

The small gas canister may need to be replaced often. And, the argon gas is expensive as is the argon regulator used to provide the argon gas to the plasma site.

BRIEF SUMMARY OF THE INVENTION

Argon is often used to purge the plasma region during LIBS measurements. An argon purge may have the advantage of enhancing signal and carrying away sputtered sample material which can contaminate internal optics. Some customers/users may desire a handheld LIBS unit which does not require replacement of the argon canister and/or which does not include an expensive argon regulator. While argon usage usually enhances the LIBS signal, there are many applications where the signal is adequate without its use. However, without gas flow, the LIBS laser typically produces sputtered sample material which can accumulate on surfaces surrounding the plasma. Handheld LIBS instruments typically include a protective barrier optic to prevent this “dirt” and contamination from entering the inner parts of the instrument. This barrier might be a clear optic (“splatter shield”) that can pass the outgoing laser light as well as the returning elemental emission wavelengths, or it might be the actual focusing elements sealed in barrier wall. In either case, a buildup of sputtered sample material will eventually occur and the barrier optic(s) will require cleaning. Otherwise, the dirty barrier optic will block the incident laser energy and/or the plasma radiation. And, firing of the laser through dirty optics can permanently fuse particulate matter to the optic thus requiring replacement or polishing.

Featured in one example is a handheld LIBS device which does not require argon canisters or an expressive argon regulator. Instead, an inexpensive air pump (e.g., available from Maxclever Electric or Boxer GmbH) has its intake exposed to the atmosphere and pumps an atmospheric gas mixture (e.g., air) to the nose cavity of the LIBS device to keep the barrier optics clean. The need to clean, replace, or polish the barrier optics is thus reduced.

Featured is a handheld LIBS device comprising a laser source for generating a laser beam, a spectrometer subsystem for analyzing a plasma generated when the laser beam strikes a sample, and a nose section including an end plate with an aperture for the laser beam and for receiving plasma radiation and an optic spaced from the end plate defining with the end plate a cavity therebetween. An atmospheric purge subsystem includes an air pump with an intake exposed to the atmosphere and a conduit connected to the air pump providing an atmospheric gas mixture to the nose section cavity to purge the cavity of contaminants and keep the optic clean as the atmospheric gas mixture exits the cavity through the end plate aperture.

In some embodiments, the end plate further includes a vent for removing the atmospheric gas mixture from the cavity. Preferably, there is no inert gas canister and/or gas regulator. The device may further include a filter for the air purge intake.

Also featured is a method comprising generating a laser beam through a transparent optic and an end plate aperture defining a cavity therebetween, analyzing a plasma generated when the laser beam strikes a sample, and while generating the laser beam, providing an atmospheric purge gas mixture to the cavity via an air pump with an intake exposed to the atmosphere and a conduit connected to the air pump providing the atmospheric gas mixture to the nose section cavity to purge the cavity of contaminants and keep the optic clean as the atmospheric gas mixture exits the cavity through the end plate aperture.

A new handheld LIBS device with atmospheric purge features a laser source for generating a laser beam, a spectrometer subsystem for analyzing a plasma generated when the laser beam strikes a sample, and a nose section with an aperture for the laser beam and for receiving plasma radiation. An atmospheric purge subsystem includes an air pump with an intake exposed to the atmosphere and a conduit connected to the air pump providing an atmospheric gas mixture to the nose section to purge the nose section of contaminants as the atmospheric gas mixture exits the nose section. In some versions the nose section includes an end plate with the aperture and a transparent optic spaced from the end plate defining with the end plate a cavity therebetween. The end plate may further include a vent formed therein for removing the atmospheric gas mixture from the cavity.

DETAILED DESCRIPTION OF THE INVENTION

Handheld LIBS device10,FIGS.1A-1Bin one example, includes housing12with nose section14terminating an end plate16with aperture18for the laser beam. Typically, focusing optics focus the laser beam at or proximate the nose plate aperture which is held against the sample to be evaluated. A plasma is created and the photons thereof enter the nose plate aperture to be evaluated by a spectrometer subsystem within housing12.

As shown in the example ofFIGS.2-3, preferably, nose section14includes apertured end plate16spaced from a transparent barrier optic (splatter shield)20defining cavity22therebetween. End plate16is flat and smooth and is shown inFIG.2abutting sample S. Laser source30provides laser beam32focused by focusing lens32to a focal point at, in, or proximate sample S after passing through end plate16aperture18. The resulting plasma radiation is detected by spectrometer subsystem36.

Additional optical components which transmit the laser beam to the sample and which transmit the plasma radiation to the spectrometer subsystem are not shown. But, see U.S. Pat. Nos. 9,719,853; 9,568,430; and 9,036,146 all incorporated herein by this reference. Controller38(for example one or more microprocessors or microcontrollers) may control laser source30and/or spectrometer subsystem36based on a trigger signal from, for example, trigger40,FIG.1which, when pressed by the user, begins a sample analysis routine wherein the laser is fired one or more times and spectral analysis on the resulting plasma is performed.

In this example, transparent shield20protects focusing optic32and other components in the device housing behind the shield from particulate matter created when the laser strikes the sample.

Featured is an atmospheric (e.g., air) purge subsystem which preferably keeps shield20cleaner. In one example, inexpensive air pump50,FIG.2has intake52with optional foam filter51exposed to the atmosphere (e.g., an air gas mixture). Pump output54is connected to a conduit such as conduit56which terminates in this example as shown at58in cavity22(with or without a nozzle) to purge the cavity of contaminants and to keep the shield20clean as the atmospheric gas mixture exits the cavity through end plate aperture18as shown at60,FIG.3.

An argon purge may be useful for detecting some elements in a sample but is not always needed for all applications. Additionally, the argon canisters must be frequently replaced and they and the argon regulator are expensive.

Here, the atmospheric gas mixture purge serves a somewhat different purpose, namely keeping the splatter shield (or other LIES optics) clean so it doesn't have to be withdrawn from the handheld LIES device and cleaned and/or replaced as often. And yet, for many elements, a sufficient signal is still generated with an air purge as opposed to an argon purge. Argon canisters and an expensive argon regulator are not needed or included. Air pump50,FIG.2costs a fraction of an argon regulator.

If the sample surface is smooth, air may not be able to escape the interface between the end plate and the sample. Thus, end plate16,FIG.1Bmay include one or more vents70in the form of grooves or the like formed in the end plate outer surface. The only escape path for the flowing air is out through the small hole in the end plate. This small volume is the same region where the plasma is occurring and so the plasma particulate residue is immediately carried out through the hole and then sideways through the grooved vent(s). Rubber anti-skid pads17a,17bmay also be incorporated onto end plate16above and below orifice18to keep the end plate on the sample without moving.

Controller38,FIG.2, may be configured (e.g., programmed) to energize air pump50during the analysis/test cycle. For example, controller38may receive a trigger signal to start a test and energize pump50before firing laser source30. After a suitable test time (e.g., after 150 laser shots), controller38may be programmed to deenergize pump50. Alternatively, controller38may be configured to deenergize pump50when no more spectral data is received from spectrometer subsystem36. Energizing the air pump only during a test saves battery power.

The positive air flow out of the cavity22through end plate16orifice18prevents particulate matter from entering cavity22and contaminating splatter shield20which would otherwise affect the transmission of laser energy through the shield and/or the transmission of plasma radiation through the shield to be detected by the spectrometer subsystem.

In other designs, the analyzer includes a nose section purged by the atmospheric (e.g., air) gas but no shield protecting the analyzer optics. For example, various barrier optics (e.g., lenses) may be exposed to the plasma and in such designs the atmospheric purge gas helps clean the optical components to avoid the need for repeated applications of a polishing paste for the lenses.

InFIG.1A, air pump50,FIG.2, may be located behind door13,FIG.1Ain housing12and foam filter51is behind the openings in the door. See alsoFIG.4. InFIG.5, pump50is held by door13and has intake52connected to the filter housing15via conduit17.FIG.6shows the door open to replace filter51if needed.