fig1 shows a taggant - based article tracking system for a supply chain , for example , which tracking system has been constructed according to the principles of the present invention . generally , in the illustrated system , during the incoming inspection by the down - stream customer , the taggants are interrogated and read with the reader to obtain information that is encoded in or represented by the taggants . the information usually concerns the origin of the articles passing through the supply chain . in one example , the information is used to verify the upstream supply or source of the articles . in one example , the taggants are interrogated with a 980 nanometer semiconductor laser and read with a microelectromechanical system ( mems ) fabry - perot tunable filter spectrometer as described in u . s . patent application ser . no . 10 / 967 , 075 , filed on oct . 15 , 2004 , entitled integrated raman spectrometer system , by xiaomei wang , which is incorporated herein by this reference . the process of reading the taggants involves determining the raman spectral response of the taggants and the comparing the response to a library of possible taggants to find a match . upon verification , the taggants are erased such that it is no longer feasible to obtain the source , inventory / article information from the taggants . this process can involve the permanent , complete destruction with the same reader or a separate eraser device . alternatively , the process can involve the substantial destruction of the taggants such that obtaining the original taggant spectrum corresponding information is near impossible or at least very difficult , possibly requiring special laboratory analysis . the erasure process is preferably accomplished by increasing the power or changing the wavelength of the reader &# 39 ; s laser radiation source so that the taggants are heated to induce chemical and / or physical changes in the taggants or a material , such as binder or vehicle , carrying the taggants , to thereby destroy the taggants &# 39 ; unique spectral features or render obtaining the unique spectral feature difficult such as by rendering a taggant substrate , taggant carrier , binder material , and / or taggant coating material opaque to the wavelength used by the reader . this feature of taggant erasure is significant — it is a security measure to prevent unauthorized subsequent use of the labels , containers , or packages . once again , the incoming inspection verification data are transmitted to the inventory management system 115 . after re - packaging , processing , or merely inventory counting , “ customer b ” becomes “ supplier b ” to down - stream “ customer c ”. the goods leaving site b will be tagged with unique taggant b . this cycle is applied at each transaction point where necessary through the whole distribution channel : from the bulk supplier to the end - user . the proposed system can be designed to fit each customer &# 39 ; s special needs . for example , separate taggants that are product - specific can be applied to the units along with the supply chain authentication taggants . these taggants are for drug authentication only and would travel through the whole distribution channel 100 unaltered . the design and manufacture of the raman - active taggants is tailored to the security application . these taggants are usually special , complex , long - chain polymers , which cannot be obtained on the open market . there are a large number of molecule classes and mixtures that can be used for the taggant manufacturing . this allows a virtually unlimited variety of taggants for use . reverse engineering of the taggants &# 39 ; chemical structure based on the observed spectrum is extremely difficult . for further security enhancement , unique taggants can be introduced as needed . security is also addressed at the reader and system levels . at the reader level , data processing and verification are preferably performed autonomously — only positive / negative authentication results are presented to the users and the information system . more importantly , this system controls the lifecycle of the taggants on the labels once they are in the distribution system by destroying the taggants at the end of designed transactions . this eliminates the possibility of empty containers , packages , or even labels being improperly or illegally reused for counterfeit drugs . compared with other authentication techniques such as direct characterization of pharmaceutical drugs themselves , the proposed solution is simpler , more manageable , and widely applicable . another significant advantage of the proposed system is that the method of applying taggants to the labels or packages can be an inkjet - like printing process , compatible with the barcode generation methods currently utilized in inventory control . this extendibility and compatibility makes the adaptation of the proposed system relatively easy . the system can also be made cost effective . with millions of products going through distribution channels , it is very important that the taggants be cost effective . compared with other technologies such as radio frequency identification ( rfid ) or optically - shifted or optically - variable pigments , secure polymer based taggants are believed to offer significantly lower cost . in more detail , fig1 shows a series of bulk suppliers a 1 , a 2 , a 3 . each of these bulk suppliers , for example , could be a drug producer or manufacturer producing drugs d 1 , d 2 , d 3 , d 4 and d 5 . in order to indicate that these drugs d 1 - d 5 are from the respective manufactures / suppliers a 1 , a 2 , a 3 , they are each labeled with taggant material 110 that identifies or represents the corresponding bulk supplier a 1 , a 2 , a 3 . then , the drugs enter the supply chain 100 . they are distributed to intermediate entities in the supply chain such as process / packaging plants b 1 / b 2 . as each of the drugs d 1 - d 5 is received , the taggants a 1 - a 3 of the bulk suppliers b 1 , b 2 are then read and analyzed by the inventory management systems 115 for each of these process packaging plants b 1 , b 2 . the information represented by the taggants is determined and checked against the information in the inventory systems 115 concerning the articles in order to confirm that the drugs were received from the proper bulk suppliers and are not counterfeit . the taggant information is also preferably cross - checked against any other information such as information encoded in bar codes on the drug packaging . in the preferred embodiment , these taggants , identifying the origin of the drugs a 1 , a 2 , a 3 , are then erased . specifically , the taggants are chemically and / or physically modified such that obtaining the original spectral response and thus the encoded information of the taggants becomes less feasible , such as impossible , to obtain . each of the processing / packaging plants , b 1 , b 2 , then labels the drugs d 1 - d 5 with their own taggants b 1 , b 2 110 . these taggants 110 are then read by the distribution centers c 1 , c 2 . the information represented by these taggants b 1 , b 2 110 is then used by the inventory systems 115 of the distribution centers c 1 , c 2 to confirm that the drugs came from the proper process / packaging plants . the taggants b 1 , b 2 are then preferably destroyed at the distribution centers c 1 , c 2 . new taggants c 1 , c 2 110 are added to the drugs d 1 - d 5 by the distribution centers c 1 , c 2 . these are then used by the entities near the end of the distribution chain , such as hospitals and pharmacies to confirm that the drugs are not counterfeit and are from the proper distribution center c 1 , c 2 , for those drugs . fig2 illustrates one example of a label for carrying the taggants of the supply chain 100 . specifically , the label 200 in the preferred embodiment comprises indicia 210 that have spatially encoded information . examples of spatially encoded information are human readable text and numbers . alternatively , machine readable systems such as the illustrated bar codes 210 are used in other embodiments . the spatially encoded information would include information such as type of drug and possibly its origin including date of manufacture . the label 200 preferably has another region such as region 150 that contains the taggants that represent the same or other information concerning the articles . in one example , the taggant material is distributed in a region of the label 150 . thus , the spatially encoded information 210 and the taggant information 150 can be obtained by one reader , interrogating the label 200 both in the optical wavelengths and by irradiating the label with the wavelengths required to obtain the raman spectra for the taggants in region 150 . in another embodiment , the actual pigments used in the spatially encoded information 210 contain the taggants . thus , the label is read both in the optical spectrum to obtain the spatially encoded information and in the raman spectral wavelengths to obtain the raman spectra . one further modification is to spatially encode the taggants such that different taggants are placed at different regions of the label 200 . for example , the different lines of the bar code have different associated a taggants , in one example , with the different taggants &# 39 ; location encoding further information . fig3 is a cross - sectional view illustrating one embodiment of the label 200 . specifically , the label 200 comprises a substrate material 10 such as paper or adhesive - backed paper or plastic film material . on this substrate 10 are the regions of pigment 210 associated with the spatially encoded information such as the imprinted bar code . the illustrated example , the taggants are disposed as a material film layer over the substrate 210 and possibly over the regions of pigment for the spatially encoded information . in one embodiment , the taggants are contained within an adhesive or glue vehicle or binder material to thereby form the taggant material layer 110 . in one embodiment , a covering 212 is provided for the taggants 110 . this covering is used to protect the taggants 110 from interaction with or exposure to the atmosphere . according to one aspect of the invention , removal of the cover 212 induces changes in the taggant material 110 . in one example , the taggants are chemically reactive such that removal of the covering 212 exposes the taggants 110 to the atmosphere such that they react , changing their spectral response and thus destroying the information represented by the taggants . in another example , the taggant material vehicle , medium , or binder material of the taggants is chemically reactive to the atmosphere such that removal of the covering causes the binder material to react or otherwise change possibly making the binder material of the taggants 110 opaque to the wavelengths used for the taggant interrogation . in still another example , removal of a light filtering covering 212 exposes the taggant material to full spectrum light that induces the changes to the taggants &# 39 ; spectra . the result is that determining the taggant raman spectrum and the information becomes infeasible with the removal of the covering 212 . fig4 illustrates one example of a taggant reader / eraser 400 . in this example , it comprises a semiconductor laser radiation source 410 , such as an approximately 980 nanometer pump laser . in the illustrated embodiment , it is coupled by a length of optical fiber 412 to a probe head 414 . this projects the laser radiation generated by the laser source to the taggant material 110 . the probe 414 also captures the returning raman spectra from the taggant material 110 and transfers it to an optical spectrum analyzer / controller 416 . this is done in one example by a fiber optic link 418 . the optical spectrum analyzer / controller 416 determines the raman spectra and then possibly either matches the spectrum to a library of spectra to determine the represented information encoded in the raman spectra or passes the raw spectral information to the inventory system 115 of the entity via a radio - frequency communications link . there , the information is used to verify the origin , for example , of the articles with which the taggant material 110 is associated . a true / false signal is then returned to the controller 416 . in the preferred embodiment , the taggant material 110 is erased by increasing the power of the laser radiation source 410 to induce chemical and / or physical changes in the taggant material , such as to the taggants or a binder material or covering material , for example , of the taggant material . these changes make reading the taggant material and obtaining the information less feasible in the future . thus , when the controller 416 is in analysis mode , it analyzes the taggant material &# 39 ; s spectral response , and when it is in an erasure mode , the controller modifies the taggant material . in other embodiments , a radiation source irradiates the taggant material with a different wavelength or has a different spectral content during the erasure mode than that used during the analysis mode , in order to render the taggant material erased or unreadable . while this invention has been particularly shown and described with references to preferred embodiments thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims .