Detection and mapping of latent fingerprints by laser-induced breakdown spectroscopy

Detection of latent fingerprints on a Si wafer by laser-induced breakdown spectroscopy (LIBS) is demonstrated using approximately 120 fs pulses at 400 nm with energies of 84 +/- 7 microJ. The presence of a fingerprint ridge is found by observing the Na emission lines from the transferred skin oil. The presence of the thin layer of transferred oil was also found to be sufficient to suppress the LIBS signal from the Si substrate, giving an alternative method of mapping the latent fingerprint using the Si emission. A two-dimensional image of a latent fingerprint can be successfully collected using these techniques.     

Quantitative comparison of terahertz emission from (100) InAs surfaces and a GaAs large-aperture photoconductive switch at high fluences

InAs has previously been reported to be an efficient emitter of terahertz radiation at low excitation fluences by use of femtosecond laser pulses. The scaling and saturation of terahertz emission from a (100) InAs surface as a function of excitation fluence is measured and quantitatively compared with the emission from a GaAs large-aperture photoconductive switch. We find that, although the instantaneous peak radiated terahertz field from (100) InAs exceeds the peak radiated signals from a GaAs large-aperture photoconductive switch biased at 1.6 kV/cm, the pulse duration is shorter. For the InAs source the total energy radiated is less than can be obtained from a GaAs large-aperture photoconductive switch.     

Spectrochemical microanalysis of aluminum alloys by laser-induced breakdown spectroscopy: identification of precipitates

Multielemental microanalysis of commercially available aluminum alloys has been performed in air by laser-induced breakdown spectroscopy (LIBS) by use of UV laser pulses with energies below 10 microJ. It is shown that the LIBS technique is capable of detecting the elemental composition of particles less than 10 microm in size, such as precipitates in an aluminum alloy matrix, by using single laser shots. Chemical mapping with a lateral resolution of approximately 10 microm of the distribution of precipitates in the surface plane of a sample was also carried out. Two main types of precipitate, namely, Mn-Fe-Cu (type I) and Mg-Cu (type II), were unambiguously distinguished in our LIBS experiments, in good agreement with x-ray microanalysis measurements. The relative standard deviations of emission of the main minor constituent elements (Cu, Mg, Mn) of the aluminum 2024 alloy range from 33% to 39% when laser shots on the precipitates are included in the analysis but decrease to a range from 5.3% to 7.4% when laser shots are taken only on the matrix material, excluding the precipitates.     

Active-passive mode locking of a flashlamp-pumped dye laser

A simple dye laser system for obtaining relatively high energy, synchronized, picosecond pulses is described. The novel combination of active and passive mode locking within a single flashlamp-pumped dye laser cavity produced 2.5 μJ, sub-10 ps pulses capable of being synchronized to an external event with better than 100 ps accuracy. The single pulse energy was subsequently increased to 40 μJ by using a larger twin flashlamp-pumped oscillator.     

Experimental and modeling studies of a Brillouin amplifier

KrF laser-pumped backward Brillouin amplification of nanosecond pulses at 248 nm is investigated both experimentally and numerically. Gain and saturation of the amplifier system are studied for an SF₆ Brillouin medium at pressures of 5 to 15 atm and 24 ns pump pulses at an intensity of ≈9 MW/cm². The input Stokes intensity is varied from 0.001 to 1.0 MW/cm². Power gains of 20 are achieved at energy extraction efficiencies of 40%. Experimental results are compared to a time dependent numerical model of pulse amplification which incorporates arbitrary pump and Stokes pulse shapes and intensities. The effect of laser bandwidth is investigated in the model calculations in order to assess its influence on Brillouin amplification     

Sensitivity of surface reflectance retrieval to uncertainties in aerosol optical properties

We formulate a procedure to investigate the sensitivity of surface reflectances retrieved from satellite sensor data to uncertainties in aerosol optical properties. Aerosol optical characteristics encompassed in the study include the aerosol optical depth, the Junge parameter (i.e., spectral dependence), and the imaginary part of the refractive index (i.e., aerosol absorption). The study includes both clear and hazy atmospheric conditions, wavelengths of 0.550 and 0.870 μm, three solar zenith angles, and five viewing geometries. Key results are presented graphically in terms of accuracy requirements on the aerosol property under consideration for a 5% uncertainty in predicted surface reflectance.     

Two photon absorption coefficients and processing parameters for photoresists

The two photon absorption (TPA) process is currently used to write high resolution microstructures for a variety of applications. Key parameters required to predict the final structure formation for this process are experimentally determined and reported in this article for two commercially available resists, Ormocore and SU-8. The measured TPA coefficients measured at 800 nm for Ormocore and SU-8 are 27 ± 6 and 28 ± 6 cm TW⁻¹, respectively. For Ormocore and SU-8 the dose required to write 35 and 50 μm high structures, respectively, were 54 ± 8 and 3.5 ± 0.5 J cm⁻³, respectively, and the measured contrasts were 15 ± 2 μm per decade J⁻¹ cm³ and 55 ± 8 μm per decade J⁻¹ cm³, respectively.     

Potential of Getis statistics to characterize the radiometric uniformity and stability of test sites used for the calibration of Earth observation sensors

The calibration of airborne and satellite remote sensing sensors is a fundamental step for the rigorous validation of products derived from satellite data. Because of the inaccessibility of Earth Observation Satellites on orbit, the direct calibration method based on a test site with ground reference data is often considered necessary. However, the problem of radiometric spatial uniformity and temporal stability of test sites constitutes an important issue in the accuracy achieved in calibration operations and the long-term characterization of satellite sensor radiometry. Generally, the coefficient of variation and semivariograms are the most widely used tools for evaluating the radiometric uniformity and stability of a calibration site. In this study, we analyze for the first time the potential of Getis statistics compared to the coefficient of variation for the study of the radiometric spatial uniformity and temporal stability of the Lunar Lake Playa, Nevada (LLPN) test site. The results obtained show the potential and the importance of the synergy generated by these two methods for analyzing the radiometric temporal stability of the LLPN site. Getis statistics provide an excellent spatial analysis of the site while the coefficient of variation provides complementary information on the temporal evolution of the site.