Mid-infrared Wavelength Region Research Articles

LESS-INVASIVE LASER THERAPY AND DIAGNOSIS USING A TABLETOP MID-INFRARED TUNABLE LASER

Since numerous characteristic absorption lines caused by molecular vibration exist in the mid-infrared (MIR) wavelength region, selective excitation or selective dissociation of molecules is possible by tuning the laser wavelength to the characteristic absorption lines of target molecules. By applying this feature to the medical fields, less-invasive treatment and non-destructive diagnosis with absorption spectroscopy are possible using tunable MIR lasers. A high-energy nanosecond pulsed MIR tunable laser was obtained with difference-frequency generation (DFG) between a Nd:YAG and a tunable Cr:forsterite lasers. The MIR-DFG laser was tunable in a wavelength range of 5.5–10 μm and generated laser pulses with energy of up to 1.4 mJ, a pulse width of 5 ns, and a pulse repetition rate of 10 Hz. Selective removal of atherosclerotic lesion was successfully demonstrated with the MIR-DFG laser tuned at a wavelength of 5.75 μm, which corresponds to the characteristic absorption of the ester bond in cholesterol esters in the atherosclerotic lesions. We have developed a non-destructive diagnostic probe with an attenuated total reflection (ATR) prism and two hollow optical fibers. An absorption spectrum of cholesterol was measured with the ATR probe by scanning the wavelength of the MIR-DFG laser, and the spectrum was in good agreement with that measured with a commercial Fourier transform infrared spectrometer.

DESIGN AND FABRICATION OF INFRARED HOLLOW FIBERS FOR SPECTROSCOPIC GAS SENSING

Infrared hollow fibers were developed for spectroscopic gas sensing.The hollow core fiber has a silver film and a dielectric film on its inner surface to enhance the reflection rate,and thus to low the transmission loss.The chemical silver mirror-reaction method and the liquid-phase coating technique were used to form the silver and the dielectric film.Low-loss properties were achieved from the visible to the mid-infrared wavelength regions by optimizing the dielectric material and the film thickness.The low-loss hollow core fiber can be used not only as the absorption cell for gas sensing but also as the transmission medium for infrared light.Primary experimental results show that the hollow fiber is a good alternative for gas cell for miniaturization in spectroscopic gas sensing.

Silicon photonic waveguides for different wavelength regions

In this paper, we present our work on three silicon waveguide structures that are suitable for three different wavelength regions: near-, mid- and far-infrared. Design rules for standard rib SOI waveguides are given. Both single mode and polarization independence in these waveguides are discussed. A hollow-core waveguide suitable for gas-sensing applications in the mid-infrared wavelength region is also analysed. Finally, fabrication and experimental results for free standing waveguides, which may find application in the mid- and perhaps far-infrared wavelength regions, are presented.

GaAsSbN–GaAsSb–InP Type-II “W” Quantum Wells for Mid-IR Emission

A GaAsSbN-GaAsSb-InP type-II ldquoWrdquo quantum well (QW) structure is proposed for achieving emission in the mid-infrared (IR) wavelength region. Simulation studies based on the band anticrossing model and a 10-band k-p Hamiltonian demonstrate that emission wavelengths as long as 3 mum could be achieved on an InP substrate, limited primarily by strain relaxation considerations. The incorporation of nitrogen into GaAsSb grown on InP leads to band-gap narrowing and a deepening of the conduction band offset. The energy band structure, interband emission wavelengths, and optical matrix elements are evaluated for a GaAsSbN-GaAsSb-InP SL structure design. A structure design utilizing the lowest Sb content for the GaAsSbN electron wells and the highest Sb content for the GaAsSb hole wells, within strain limitations, provides the longest wavelength emission. The electron and hole effective masses of bulk GaAsSbN are extracted from the computed energy band structure as a function of Sb and N composition. The electron effective mass of GaAsSbN is found to remain nearly constant with N for low N-composition alloys. The heavy- and light-hole effective masses decrease slightly with increasing N composition.

Germanate glass as a window for high energy laser systems

A modified Barium Gallo-Germanate glass has been developed as an exit window for high energy lasers operating in the mid-infrared wavelength region. All the physical properties, for application as a window for high energy laser systems have been measured. Absorption loss and thermo-optic coefficient were identified as key in developing the Barium Gallo-Germanate glass for high energy laser applications. A purification method was developed to reduce the absorption loss of the glass from 6x10(-2) cm(-1) to 2x10(-3) cm(-1) at 3.8 mum. Manufacturability in large size windows has been demonstrated with the fabrication of an 18" diameter prototype window. Modified Barium Gallo-Germanate glasses have also been developed with lower thermo-optic coefficient resulting in lower optical path distortion.

Grape and wine analysis - enhancing the power of spectroscopy with chemometrics..

Spectroscopic techniques offer the potential to simplify and reduce analytical times for a range of grape and wine analytes. It is this aspect, together with the ability to simultaneously measure several analytes, which was the impetus for developing spectroscopic methods. The Australian Wine Research Institute (AWRI) has long used spectroscopic analysis of wines in the ultraviolet (UV) and visible (Vis) wavelengths, and since 1998 has been investigating applications of spectroscopic techniques in the near infrared (NIR) and mid-infrared (MIR) wavelength regions of the electromagnetic spectrum for the rapid analysis and quality control of both grapes and wine by the Australian wine industry. This paper reviews the use of several spectroscopic techniques, including NIR, MIR, and Vis, combined with chemometrics, to assess grape and wine composition in the Australian wine industry. The achievements, current research, and proposed further applications of different spectroscopic techniques are discussed in studies into the assessments of red grape composition and of fungal diseases in grapes, monitoring phenolic compounds during red wine fermentations, quality grading of red, white and fortified wine styles, monitoring wine distillation processes, and yeast strain classification.

In-flight validation of mid- and thermal infrared data from the Multispectral Thermal Imager (MTI) using an automated high-altitude validation site at Lake Tahoe CA/NV, USA

The Multispectral Thermal Imager (MTI) is a 15-band satellite-based imaging system. Two of the bands (J, K) are located in the mid-infrared (3-5 /spl mu/m) wavelength region: J, 3.5-4.1 /spl mu/m and K, 4.9-5.1 /spl mu/m, and three of the bands (L, M, N) are located in the thermal infrared (8-12 /spl mu/m) wavelength region: L, 8.0-8.4 /spl mu/m; M, 8.4-8.8 /spl mu/m; and N, 10.2-10.7 /spl mu/m. The absolute radiometric accuracy of the MTI data acquired in bands J-N was assessed over a period of approximately three years using data from the Lake Tahoe, CA/NV, automated validation site. Assessment involved using a radiative transfer model to propagate surface skin temperature measurements made at the time of the MTI overpass to predict the vicarious at-sensor radiance. The vicarious at-sensor radiance was convolved with the MTI system response functions to obtain the vicarious at-sensor MTI radiance in bands J-N. The vicarious radiances were then compared with the instrument measured radiances. In order to avoid any reflected solar contribution in the mid-infrared bands, only nighttime scenes were used in the analysis of bands J and K. Twelve cloud-free scenes were used in the analysis of the data from the mid-infrared bands (J, K), and 23 cloud-free scenes were used in the analysis of the thermal infrared bands (L, M, N). The scenes had skin temperatures ranging between 4.4 and 18.6/spl deg/C. The skin temperature was found to be, on average, 0.18/spl plusmn/0.36 degC cooler than the bulk temperature during the day and 0.65/spl plusmn/0.31 degC cooler than the bulk temperature at night. The smaller skin effect during the day was attributed to solar heating. The mean and standard deviation of the percent differences between the vicarious (predicted) at-sensor radiance convolved to the MTI bandpasses and the MTI measured radiances were -1.38/spl plusmn/2.32, -2.46/spl plusmn/1.96, -0.04/spl plusmn/0.78, -1.97/spl plusmn/0.62, -1.59/spl plusmn/0.55 for bands J-N, respectively. The results indicate that, with the exception of band L, the instrument measured radiances are warmer than expected.

ISOCAM Observations of Globular Clusters in the Magellanic Clouds: The Data

Seventeen globular clusters in the Large and Small Magellanic Clouds were observed in the mid-infrared wavelength region with the ISOCAM instrument on board the Infrared Space Observatory (ISO). Observations were made using the broadband filters LW1, LW2, and LW10, corresponding to the effective wavelengths of 4.5, 6.7, and 12 mum, respectively. We present the photometry of point sources in each cluster, as well as their precise positions and finding charts.

MBE growth and characterization of type-II InAs/GaSb superlattices for mid-infrared detection

Type-II InAs/GaSb superlattices (SLs) made of 10 InAs monolayers (MLs) and 10 GaSb MLs, designed to have a cut-off wavelength of 5.4 μm, have been grown on GaSb substrates by solid source molecular beam epitaxy (MBE). In order to obtain lattice-matched structures, a thin layer of InSb was inserted at the GaSb on InAs interface. We demonstrate that structural and optical properties of such structures strongly depend on the thickness of the InSb inserted layer. Strain-balanced InAs/GaSb SLs could be grown, after optimizing the MBE shutter sequence, by using a growth temperature of 390 °C and an inserted InSb layer of thickness 1 ML. Non-optimized pin diodes using 100 periods of such an SL as absorbing material showed an absorption coefficient varying from 4×10 3 to 6×10 3 cm −1 at room temperature in the 3–5 μm mid-infrared wavelength region, and a photovoltaic response up to 230 K.

Molecular-beam epitaxy growth of quantum cascade lasers on (111)B substrates for second harmonic generation

The growth conditions for realizing quantum cascade lasers on (111)B tilted GaAs substrates by molecular beam epitaxy are analyzed. AlGaAs/GaAs(111)B unipolar lasers emitting at 11.5 μm are fabricated and show encouraging performances which allow the nonlinear susceptibility of bulk GaAs to be exploited. The emission of coherent light at 5.75 μm is obtained by intracavity frequency doubling. Frequency doubling in quantum cascade lasers on (111) oriented substrates is very attractive and can be an alternative way to access the short mid-infrared wavelength region (3–4 μm).

Optimizing boron implantation dose of HgCdTe infrared detectors

Using the material chip technology,large area photodiodes of n-on-p structure with different boron implantation dose are fabricated on the Hg1-xCdxTe film for mid-infrared wavelength region(x=0.291).Current-voltage characteristics of the photodiodes are measured at 77K and zero bias resistance-area products of different photodiodes are fitted from the data in the voltage range of -0.2—0.08V.The study indicated that the R0A products of different elements depended distinctly upon the implanted boron dose.A large R0 value has also obtained in another chip with x=0.2743.All the samples in this study are grown by Riber 32P molecular-beam epitaxy system and all the junctions-forming process is same to the standard planar technology but using a series of metallic masks during the boron ion implantation.

Double-heterojunction photodetector for midinfrared applications: theoretical model and experimental results

We report a theoretical model for characterization of a double heterojunction (DH) photovoltaic detector for application in the midinfrared (MIR) wavelength region. The physics-based closed-form model developed here has been applied to study the characteristics of an n(+)-InAsSbP-n(0)-InAsSb-p(+)-InAsSbP DH detector grown by liquid-phase epitaxy (LPE) for possible application in the 2- to 5-mum wavelength region. The results obtained from the experimental measurements have been compared and contrasted with those predicted on the basis of the theoretical model. The model can be used to explain the various physical mechanisms that shape the characteristics of the device under room-temperature operation. It can also be used to optimize the performance of the photodetector to suit specific requirements. The study reveals that compositional grading in the active and the cladding regions of a DH grown by LPE is responsible for the reduction of the responsivity and detectivity of the device in the shorter wavelength region. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Time-Resolved Absorption Study on the Photocarrier Generation Process in Layered Organic Photoreceptors: A Role of Delocalized Holes in Photocarrier Generation

We have applied time-resolved absorption spectroscopy to the study on the photocarrier generation process in layered organic photoreceptors. The photoreceptors are comprised of azo-pigments as charge generation materials (CGMs) and charge transport materials (CTMs). Two or three distinct transient absorptions ranging from visible to mid-infrared wavelength region (600 – 2500 nm) were observed after photoexcitation in these photoreceptors. We ascribed all these transients to the cationic species of CTMs from the results of the measurements in various conditions. The transient absorption spectrum showed remarkable dependence on the CTM concentration. From this observation, we concluded that the cationic species of CTMs were monomer, dimer and larger aggregate cations. The latter two cationic species are regarded as the holes delocalized within some CTM molecules. The role of delocalized holes in photocarrier generation is discussed from the decay dynamics.

Study of the current-voltage characteristics of n-on-p junction fabricated by pr oton-implanted molecular beam epitaxial Hg1-xCdxTe

Large area n-on-p structures of p-n junction with different proton implantation doses are fabricated on the moleculer beam epitaxial grown HgCdTe films for mid-infrared wavelength region. Current-voltage characteristics of the p-n junction are measured at 77K. The zero-bias resistance-area product (R0A ) of 312.5Ω·cm2 is obtained when the proton implantation dose is 2×10 15cm-2， and R0A increases to 490Ω·cm2 after ann ealing at low temperatures.

A versatile photoacoustic spectrometer for sensitive trace-gas analysis in the mid-infrared wavelength region (5.1-8.0 and 2.8-4.1 μm)

A versatile CO laser-based photoacoustic spectrometer is presented equipped with three photoacoustic cells placed inside the laser cavity. The newly designed CO laser can operate both in the Δv=1 and the Δv=2 modes (5.1–8.0 μm and 2.8–4.1 μm) on 400 laser lines. Improved laser operation originating from a better cooling of the gas discharge was evidenced by a shift of the laser output power to lower J-values. Due to the wide emission range of the source, many molecules of biological and atmospheric interest, including methane and ethane, can be detected with sensitivities typically at the (sub)ppb level. Measurement of the respiration of a cockroach showed that the spectrometer is not only sensitive, but also has a good time response (8 s at a flow rate of 10 l/h).

Photoacoustic spectrometer based on a Planckian radiator with fast time response

We have developed a photoacoustic spectrometer based on a fast responding Planckian radiator. This promising radiation source represents a matrix of 35 tiny resistors ( 0.500 mm×0.357 mm) that emit their peak power in the mid-infrared wavelength region and that can be directly modulated via their current. It enables a simple, compact and robust detector for monitoring of trace gases like carbon dioxide (CO 2).

Wide single-mode tuning of a 30–38-µm, 700-mW, continuous-wave Nd:YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.

New infrared spectroscopic beamline at BESSY II

At BESSY a multipurpose infrared (IR) beamline is being built for biological and materials science investigations. It will provide useful IR intensities over the energy range from about 10 000 down to 50 cm−1 and lower. After commissioning the first beamline section in the spring of this year first quantitative measurements on the performance have been made in the near and mid-infrared wavelength region.

Multiple subband transitions and evidence for population inversion in InAs/In(As,Sb) heterostructures

We report on improved InAs/InAs1−xSbx heterostructure single quantum well emitters for the mid-infrared wavelength region. An InAlAs barrier layer has been incorporated into the active region of the structures for improved electron confinement. With room temperature pulsed power outputs of 140 μW at a wavelength of 4.3 μm, an improvement of more than a factor of 6 has been achieved compared to similar structures without the barrier layer. Magneto-electroluminescence measurements at 4 K reveal the presence of multiple subband transitions in the spectra. Based on a k⋅p model assuming a type-IIa band offset, these transitions are identified as (e1,hh1) and (e1,lh1). The observation of these multiple transitions is shown to be strong evidence for population inversion in the structures.

Volume Absorption Effect for Micro Drilling of Semi-Transparent Materials

Broad tunability of the infrared free electron laser will open a new scheme of material removal from solid target. In the mid infrared wavelength region, there are various materials with variety of the optical absorption coefficient. In the FEL ablation process, Si micro drilling with smaller diameter and increased depth would be realized. The micro drilling experiments of various semi-transparent materials will be discussed relating with the volume absorption effect.