Arson presents a challenging crime scene for fire investigators worldwide. Key to the investigation of suspected arson cases is the analysis of fire debris for the presence of accelerants or ignitable liquids. This st...Arson presents a challenging crime scene for fire investigators worldwide. Key to the investigation of suspected arson cases is the analysis of fire debris for the presence of accelerants or ignitable liquids. This study has investigated the application and method development of vapor phase mid-Infrared (mid-IR) spectroscopy using a field portable quantum cascade laser (QCL) based system for the detection and identification of accelerant residues such as gasoline, diesel, and ethanol in fire debris. A searchable spectral library of various ignitable fluids and fuel components measured in the vapor phase was constructed that allowed for real-time identification of accelerants present in samples using software developed in-house. Measurement of vapors collected from paper material that had been doused with an accelerant followed by controlled burning and then extinguished with water showed that positive identification could be achieved for gasoline, diesel, and ethanol. This vapor phase mid-IR QCL method is rapid, easy to use, and has the sensitivity and discrimination capability that make it well suited for non-destructive crime scene sample analysis. Sampling and measurement can be performed in minutes with this 7.5 kg instrument. This vibrational spectroscopic method required no time-consuming sample pretreatment or complicated solvent extraction procedure. The results of this initial feasibility study demonstrate that this portable fire debris analyzer would greatly benefit arson investigators performing analysis on-site.展开更多
Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals...Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.展开更多
A room-temperature broadly tunable mid-infrared difference frequency laser source for highly sensitive trace gas detection has been developed recently in our laboratory. The mid-infrared laser system is based on quasi...A room-temperature broadly tunable mid-infrared difference frequency laser source for highly sensitive trace gas detection has been developed recently in our laboratory. The mid-infrared laser system is based on quasi-phase-matched (QPM) difference frequency generation (DFG) in a multi- grating, temperature-controlled periodically poled LiNbO3 (PPLN) crystal and employs two near-infrared diode lasers as pump sources. The mid-infrared coherent radiation generated is tunable from 3.2 μm to 3.7 μm with an output power of about 100 μW. By changing one of the pump laser head with another wavelength range, we can readily obtain other needed mid-infrared wavelength range cover. The performance of the mid-infrared laser system and its application to highly sensitive spectroscopic detection of CH4, HCI, CH2O, and NO2 has been carried out. A multi-reflection White cell was used in the experiment gaining ppb-level sensitivity. The DFG laser system has the features of compact, room-temperature operation, narrow line-width, and broadly continuous tunable range for potential applications in industry and environmental monitoring.展开更多
In this work, a 532 nm diode CW laser is used to heat samples used as building materials at a 1 meter standoff distance while using an FLIR (Forward-Looking Infrared) thermal camera to monitor and record the heating a...In this work, a 532 nm diode CW laser is used to heat samples used as building materials at a 1 meter standoff distance while using an FLIR (Forward-Looking Infrared) thermal camera to monitor and record the heating and then cooling of each sample after lasers are switched off. The data is then analyzed using FLIR proprietary software. Since the absorption spectra of materials are unique, using multiple lasers of different wavelengths to simultaneously shine onto the sample at different locations would give enough thermal data to successfully characterize the samples within a reasonable amount of time. The results are very promising for applications involving non-destructive detection and classification of materials.展开更多
Contrary to the conventional detection method like radiography,the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel,dentin,and caries lesion...Contrary to the conventional detection method like radiography,the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel,dentin,and caries lesion.In this paper,three light sources with different bandwidths based on a transillumination method are compared.The contrast among enamel,dentin,and caries lesion is calculated in different situations.The experimental results show that the random fiber laser has the best comprehensive quality in dental imaging due to its high spectral density,low coherence,and deep penetration.This work provides a guidance for light source selection in dental imaging.展开更多
Photoacoustic waves from hemoglobin solutions in dental roots are detected by using a 1064-nm laser and an ultrasonic soft probe based on a composite transducer on the tooth surface. The high-frequency ultrasonic wave...Photoacoustic waves from hemoglobin solutions in dental roots are detected by using a 1064-nm laser and an ultrasonic soft probe based on a composite transducer on the tooth surface. The high-frequency ultrasonic waves are detected from a tooth with a hemoglobin solution in the pulp cavity due to the large heat transfer coefficient and absorption coefficient of hemoglobin. The spectral intensities of frequency components higher than 1 MHz show good correlation with the hemoglobin solution concentrations, and maps of frequency spectra calculated by taking short-time Fourier transforms clearly exhibit the effect of absorbance in dental pulp.展开更多
文摘Arson presents a challenging crime scene for fire investigators worldwide. Key to the investigation of suspected arson cases is the analysis of fire debris for the presence of accelerants or ignitable liquids. This study has investigated the application and method development of vapor phase mid-Infrared (mid-IR) spectroscopy using a field portable quantum cascade laser (QCL) based system for the detection and identification of accelerant residues such as gasoline, diesel, and ethanol in fire debris. A searchable spectral library of various ignitable fluids and fuel components measured in the vapor phase was constructed that allowed for real-time identification of accelerants present in samples using software developed in-house. Measurement of vapors collected from paper material that had been doused with an accelerant followed by controlled burning and then extinguished with water showed that positive identification could be achieved for gasoline, diesel, and ethanol. This vapor phase mid-IR QCL method is rapid, easy to use, and has the sensitivity and discrimination capability that make it well suited for non-destructive crime scene sample analysis. Sampling and measurement can be performed in minutes with this 7.5 kg instrument. This vibrational spectroscopic method required no time-consuming sample pretreatment or complicated solvent extraction procedure. The results of this initial feasibility study demonstrate that this portable fire debris analyzer would greatly benefit arson investigators performing analysis on-site.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61078005)the National Basic ResearchProgram of China (Grant No. 2007CB613205)the China Postdoctoral Science Foundation
文摘Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.
基金supported by National Natural Science Foundation of China under Grant No. 50534050the Key Project of the Chinese Academy of Sciences under Grant No. KJCX2-SW-W27.
文摘A room-temperature broadly tunable mid-infrared difference frequency laser source for highly sensitive trace gas detection has been developed recently in our laboratory. The mid-infrared laser system is based on quasi-phase-matched (QPM) difference frequency generation (DFG) in a multi- grating, temperature-controlled periodically poled LiNbO3 (PPLN) crystal and employs two near-infrared diode lasers as pump sources. The mid-infrared coherent radiation generated is tunable from 3.2 μm to 3.7 μm with an output power of about 100 μW. By changing one of the pump laser head with another wavelength range, we can readily obtain other needed mid-infrared wavelength range cover. The performance of the mid-infrared laser system and its application to highly sensitive spectroscopic detection of CH4, HCI, CH2O, and NO2 has been carried out. A multi-reflection White cell was used in the experiment gaining ppb-level sensitivity. The DFG laser system has the features of compact, room-temperature operation, narrow line-width, and broadly continuous tunable range for potential applications in industry and environmental monitoring.
文摘In this work, a 532 nm diode CW laser is used to heat samples used as building materials at a 1 meter standoff distance while using an FLIR (Forward-Looking Infrared) thermal camera to monitor and record the heating and then cooling of each sample after lasers are switched off. The data is then analyzed using FLIR proprietary software. Since the absorption spectra of materials are unique, using multiple lasers of different wavelengths to simultaneously shine onto the sample at different locations would give enough thermal data to successfully characterize the samples within a reasonable amount of time. The results are very promising for applications involving non-destructive detection and classification of materials.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.11974071 and 61635005)in part by Sichuan Science and Technology Program(Grant No.2018HH0148)。
文摘Contrary to the conventional detection method like radiography,the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel,dentin,and caries lesion.In this paper,three light sources with different bandwidths based on a transillumination method are compared.The contrast among enamel,dentin,and caries lesion is calculated in different situations.The experimental results show that the random fiber laser has the best comprehensive quality in dental imaging due to its high spectral density,low coherence,and deep penetration.This work provides a guidance for light source selection in dental imaging.
文摘Photoacoustic waves from hemoglobin solutions in dental roots are detected by using a 1064-nm laser and an ultrasonic soft probe based on a composite transducer on the tooth surface. The high-frequency ultrasonic waves are detected from a tooth with a hemoglobin solution in the pulp cavity due to the large heat transfer coefficient and absorption coefficient of hemoglobin. The spectral intensities of frequency components higher than 1 MHz show good correlation with the hemoglobin solution concentrations, and maps of frequency spectra calculated by taking short-time Fourier transforms clearly exhibit the effect of absorbance in dental pulp.
