Latent fingerprint detection

Abstract

Systems, devices, and methods for detecting a contaminant on a substrate are discussed herein. Variations of such systems, devices, and methods may include one or more illumination sources that emit illumination at one or more desired wavelength ranges to illuminate one or more areas on the substrate; where the desired wavelength range is one that is absorbed by the contaminant while causing the substrate to fluoresce. Such fluorescence may be detected with a visible-spectrum detector, which will also detect the contaminant as a darker contrast area against the fluorescence. In some variations, an illumination source includes a broad-spectrum light source and a waveband filtering device that filters all but the desired illumination waveband out of the broad-spectrum light generated by the broad-spectrum light source.

1 . A device for detecting a contaminant on a substrate, the device comprising:
 an illumination source that emits illumination at a desired wavelength range to illuminate an area on the substrate;   wherein the desired wavelength range is one that is absorbed by the contaminant while causing the substrate to fluoresce; and   a visible-spectrum imaging device that captures an image of the illuminated contaminant contrasted against the fluorescing substrate;   wherein the illumination source includes a broad-spectrum light source and a waveband filtering device that filters all but the desired illumination waveband out of the broad-spectrum light generated by the broad-spectrum light source.   
     
     
         2 . The device of  claim 1 , where wherein, the waveband filtering device comprises a first optical element having a waveband-specific dielectric coating on a first reflecting surface such that the optical element reflects only the desired illumination waveband from the first reflecting surface; and
 wherein the emitted illumination includes light reflected from the first reflecting surface.   
     
     
         3 . The device of  claim 2 , where wherein the first optical element comprises a first mirror and wherein the first reflecting surface is a front surface of the first mirror 
     
     
         4 . The device of  claim 3 , wherein the first mirror is a wedge-shaped mirror having a wedge angle that creates total internal reflection with respect to any light reflected from a back surface of the mirror. 
     
     
         5 . The device of  claim 2 , wherein the optical element comprises a first prism and wherein the first reflecting surface is a surface of the prism. 
     
     
         6 . The device of  claim 1 , wherein the waveband filtering device further comprising a second optical element substantially similar to the first optical element;
 wherein the first optical element is configured to filter light from the illumination source;   wherein the second optical element is configured to filter light reflected by the first mirror; and   wherein the emitted illumination includes light reflected by the second mirror.   
     
     
         7 . The device of  claim 1 , wherein the imaging device is a portable camera, the illumination source is mounted to the imaging device, and the device further comprises:
 an illumination source driver that drives the illumination source in response to an activation pulse;   a power source that provides power to the illumination source driver and the illumination source; and   a trigger circuit that controls activation pulse width and activation pulse rate of the illumination source.   
     
     
         8 . The device of  claim 1 , wherein the broad-spectrum light source is a xenon flash lamp. 
     
     
         9 . The device of  claim 1 , wherein the illumination source comprises:
 a light-proof housing disposed around the broad-spectrum light source and the waveband filtering device; and   a first baffle disposed between the broad-spectrum light source and the waveband filtering device, the first baffle being configured to exclude light emitted by the broad spectrum light source but not filtered by the waveband filtering device from the emitted illumination.   
     
     
         10 . The device of  claim 9 , the device further comprising a second baffle disposed between the waveband filtering device and an illumination output aperture of the light-proof housing;
 the emitted illumination exiting the light-proof housing through the output aperture; and   the second baffle being configured to exclude light scattered inside the light-proof housing from the emitted illumination.   
     
     
         11 . The device of  claim 9 , the device further comprising a negative lens disposed between the broad-spectrum light source and the first baffle, the lens being configured to establish a desired field of view for the emitted illumination. 
     
     
         12 . The device of  claim 7 , wherein the trigger circuit is configured to provide an activation pulse width that causes the broad-spectrum light source to emit the desired waveband while limiting emission of wavebands which the waveband filtering device is configured to filter out. 
     
     
         13 . The device of  claim 1 , wherein the contaminant remains untreated with any chemicals or contrast agents prior to illumination. 
     
     
         14 . (canceled) 
     
     
         15 . The device of  claim 1 , wherein the waveband filtering device comprises an optical absorption portion that absorbs portions of the broad spectrum illumination outside of the desired illumination waveband. 
     
     
         16 . The device of  claim 2 , where the optical element is made of filter glass. 
     
     
         17 - 23 . (canceled) 
     
     
         24 . A method of detecting a contaminant on a substrate, the method comprising:
 emitting illumination in a broad-spectrum at a desired wavelength range to illuminate an area on the substrate, wherein the desired wavelength range is one that is absorbed by the contaminant while causing the substrate to fluoresce;   filtering all but a desired illumination waveband out of the broad-spectrum light while emitting illumination; and   capturing a visible-spectrum image of the illuminated contaminant contrasted against the fluorescing substrate.   
     
     
         25 . The method of  claim 24 , said filtering further comprises reflecting the broad-spectrum light with a first optical element having a waveband-specific dielectric coating on a first reflecting surface such that only the desired illumination waveband is reflected from the first reflecting surface. 
     
     
         26 . The method of  claim 25 , said reflecting further comprises directing light outside of the desired illumination waveband along an optical path other than that followed by the desired illumination waveband such that light outside of the desired illumination waveband is excluded from the emitted illumination. 
     
     
         27 . The method of  claim 24 , further comprising reflecting the first-reflected light with a second optical element having the waveband-specific dielectric coating. 
     
     
         28 . (canceled) 
     
     
         29 . The method of  claim 24 , further comprising:
 suppressing a portion of the broad-spectrum light before the broad-spectrum light reaches the waveband filtering device such that light emitted by the broad spectrum light source but not filtered by the waveband filtering device is suppressed from the emitted illumination.   
     
     
         30 . The method of  claim 24 , wherein the broad-spectrum light is generated with a flash lamp; and wherein emitting illumination in a broad-spectrum further comprises:
 providing an activation pulse to the flash lamp, the activation pulse having a pulse width that causes the flash lamp to emit the desired waveband while limiting emission of wavebands which the waveband filtering device is configured to filter out.   
     
     
         31 . The method of  claim 24 , further comprising maintaining the contaminant untreated with any chemicals or contrast agents prior said emitting. 
     
     
         32 . The method of  claim 24 , wherein filtering further comprises passing all but the desired illumination waveband of the broad-spectrum light through filter glass. 
     
     
         33 - 39 . (canceled)