Mid-infrared Free Electron Laser Research Articles

Low-invasive Soft Tissue Incision with 6.1.MU.m-light Irradiation-Gelatin Ablation Properties-

For low-invasive laser treatment, stable absorption properties of tissue during laser treatment are essentially needed, which enable us to predict irradiation effect (ablation depth, thermally-altered depth) using them. There are water and proteins as main absorber in the mid-infrared range. During laser treatment, the absorption properties of soft tissue are changed due to laser-induced temperature rise and leading to the induction of unexpected irradiation effects. We have proposed and demonstrated a novel, low-invasive laser surgery with 6.1-μm-light irradiation. 6.1-μm-light can resonantly excite both OH bending (water) and amide-I (proteins). The absorption properties of soft tissue during laser treatment would be come considerably stable because they do not remarkably depend on the surrounding temperature and the water concentration. We examined the gelatin ablation properties by λ=6.1-μm irradiation using a tunable mid-infrared Free-Electron Laser and showed that λ=6.1-μm irradiation is one of the candidates for a low-invasive soft tissue incision. Gelatins were used as a model substrate for soft tissue. From these experiments, it was found as follows. (1) Enhanced gelatin ablation occurred near λ=6.1-μm, but not λ=6.45-μm (Amide II of proteins). (2) The gelatins were removed due to water vaporization, which is reflected in the static absorption properties of the gelatin before laser irradiation. Thus, we showed the applicability of λ=6.1-μm -light for a new light source to realize a low-invasive soft tissue incision.

Free-electron-laser-based biophysical and biomedical instrumentation

A survey of biophysical and biomedical applications of free-electron lasers (FELs) is presented. FELs are pulsed light sources, collectively operating from the microwave through the x-ray range. This accelerator-based technology spans gaps in wavelength, pulse structure, and optical power left by conventional sources. FELs are continuously tunable and can produce high-average and high-peak power. Collectively, FEL pulses range from quasicontinuous to subpicosecond, in some cases with complex superpulse structures. Any given FEL, however, has a more restricted set of operational parameters. FELs with high-peak and high-average power are enabling biophysical and biomedical investigations of infrared tissue ablation. A midinfrared FEL has been upgraded to meet the standards of a medical laser and is serving as a surgical tool in ophthalmology and human neurosurgery. The ultrashort pulses produced by infrared or ultraviolet FELs are useful for biophysical investigations, both one-color time-resolved spectroscopy and when coupled with other light sources, for two-color time-resolved spectroscopy. FELs are being used to drive soft ionization processes in mass spectrometry. Certain FELs have high repetition rates that are beneficial for some biophysical and biomedical applications, but confound research for other applications. Infrared FELs have been used as sources for inverse Compton scattering to produce a pulsed, tunable, monochromatic x-ray source for medical imaging and structural biology. FEL research and FEL applications research have allowed the specification of spin-off technologies. On the horizon is the next generation of FELs, which is aimed at producing ultrashort, tunable x rays by self-amplified spontaneous emission with potential applications in biology.

The Thermal Dissociation of Cholesterol Esters using a 5.75-µm-Free Electron Laser

In order to estimate the optimum laser conditions for efficient dissociation of cholesterol ester in an arteriosclerotic region of blood vessels, we have investigated the relationship between laser wavelength and power density on cholesterol ester dissociation using a mid infrared free electron laser (MIR-FEL). In this study, cholesteryl oleate, which is a typical cholesterol ester found in arteriosclerotic regions, was irradiated with 5.75-µm-FELs, which cause vibration of ester bonds. Two results were obtained. (1) Ester dissociated depending on the absorption coefficient, and the macropulse duration was shorter than the thermal relaxation time, showing that ester bonds dissociated into carboxylic acid and cholesterol by macropulse-induced thermal effects without accompanying thermal diffusion. (2) Using a wavelength of 5.75 µm, the maximum ester dissociation ratio was achieved under the optimum laser conditions of a macropulse energy density of 0.4–1.0 J/cm2. We conclude that MIR pulsed-lasers with a wavelength of 5.75 µm can be useful for removal of cholesteryl ester in an arteriosclerotic region of blood vessels.

Wavelength and average power density dependency of the surface modification of root dentin using an MIR-FEL.

Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and power density, required for surface modification. The key aspect is to bring about effective surface modification of the root dentin while minimizing the unwanted removal of the underlying dentin. Using a tunable, MIR Free Electron Laser with lambda = 8.8-10.6 microm, we have investigated macroscopically the extent of the surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition. The observations showed that the surface modification of root dentin was inclined toward well-recrystallized HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be approximately in the wavelength region around lambda = approximately 9.0 or approximately 9.7 microm and in the average power density region of approximately 10-20 W/cm2 (resulting in total energy density and peak power density regions of approximately 1-2 kJ/cm2 and approximately 0.67-1.2 kW/cm2). The surface modification of root dentin strongly depends on the laser parameters applied. We conclude that the optimum wavelengths for laser treatment of root surface caries are lambda = approximately 9.0 or approximately 9.7 microm, corresponding to the absorption peak due to P-O stretching.

Gelatin ablation wavelength dependency in the range of 5.6–6.7 μm using a mid-infrared Free Electron Laser

Efficient and precise ablation of soft tissue is needed for non-invasive dermatological and corneal surgeries. Previous research has revealed that smooth and efficient cutting of certain soft tissues and gelatin is possible using a Free Electron Laser (FEL) with a wavelength of λ=6.45μm, tuned to the amide-II band of protein. Gelatin ablation experiments have been carried out using a mid-infrared FEL within the waveband λ=5.6–6.7μm by changing the primary absorbers such as water (λ=6.1μm) and protein (λ=6.45μm). The gelatin with 80wt% water was efficiently ablated by FEL irradiation with the waveband λ=∼5.95–6.19μm. On the other hand, using irradiation within λ=∼6.4–6.6μm, many small bubbles were observed in the irradiated volume, and the gelatin was not ablated but significantly melted. Thus, it was found that the most effective wavelength was ∼6.1μm, not ∼6.45μm, in order to cut soft tissue with a high water concentration at the expense of surface smoothness.

Medical Application Research Using a Mid-Infrared Free Electron Laser

A mid-infrared Free Electron Laser (MIR-FEL) has potentials for medical application research. The MIR-FEL has great two advantages: (1) tunability and (2) double pulse structure. The Osaka MIR-FEL is tunable from 5 to 17 μm, and produces a macropulse, composed of a train of micropulses, each approximately 5 ps long and separated by 44.8 ns. (1) Since there exist main absorbers such as water, protein, and apatite in the tissue, wavelength tunability leads to a choice of the primary absorber. (2) Laser-tissue interactions are mainly determined by the power density of the laser used. Therefore the interactions can be precisely controlled by a combination of the energy density and pulse duration of the macropulse, and the repetition rate of the micropulse. Thus, the MIR-FEL can carefully optimize the laser conditions for a non-invasive treatment without accompanying side and adverse effects by individually controlling the FEL parameters (wavelength, power density, repetition rate).

中赤外自由電子レーザーを用いたプロテオミクス応用研究

As an emerging field of molecular biology, proteomics gives a great impact on pharmaceutics, medicine and life science. The objectives of proteomics include protein identification and quantification, profiling of expression dynamics and localization, mapping of post-translational modifications, and probing of protein-ligand interactions. Because of tremendous complexity and diversity of protein world, proteomics requires high-throughput analytical technologies, which basically consist of gel electrophoresis, in-gel digestion, mass spectrometry and bio-informatics based on genome database. There are two aspects in which mid-infrared free-electron laser (MIR-FEL) can facilitate proteomics study: being used as a desorption laser in matrix-assisted laser desorption/ionization (MALDI) and as an activation laser in infrared multi-photon dissociation (IRMPD). This commentary article describes how MIR-FEL can be of benefit to proteomics, and indicates an ideal approach utilizing MIR-FEL to the goal of proteomics.

Isotope Separation of Silicon by Use of Mid-Infrared Free Electron Laser

Mid-infrared free electron laser (MIR-FEL) is an attractive light source for laser isotope separation because of its wavelength tunability and high output pulse energy. Several demonstrations have already done in the world FEL facilities. In this review, the recent results of isotope separation by use of MIR-FEL are described with our experimental result of silicon isotope separation by use of phenyltrifluorosilane.

Preface to the Special Issue on Mid-Infrared Free Electron Laser and Its Application Research

Preface to the Special Issue on Mid-Infrared Free Electron Laser and Its Application Research

Carrier Dynamics in Semiconductors under MIR FEL Excitation

Free electron lasers have unique advantages; wide-range wavelength tunability, ultrashort pulse operation and intense peak power. The high-power coherent laser beam in the mid-infrared (MIR) region provides unique opportunities to investigate carrier dynamics in semiconductors. Band-gap luminescence from a variety of compound semiconductors has been observed with an intense MIR radiation beam being directed to the samples. The band-gap luminescence is attributed to impact-ionization following scattering-induced free-electron heating.

Infrared laser ablation and ionization of water clusters and biomolecules from ice

We demonstrate the direct desorption and ionization of angiotensin II from frozen water ice samples without supplementary matrix, using a pulse train of approximately 340 intense (∼10 9 W/cm 2) picosecond pulses from a tunable, mid-infrared free-electron laser, at a wavelength of 5.9 μm. The pulse train was delivered at equally spaced intervals over a total duration of 120 ns. Ions thus formed were detected using a reflectron time-of-flight mass spectrometer. Single-shot ablation at spatially separated locations on the ice surface produced parent ions as well as Na and K adducts. Multiple pulse impact at a single location on the ice generated the parent ion signal and also protonated water clusters of the form (H 2O) n−1 H 3O +. Investigations of clusters produced by infrared laser ablation of frozen trifluoroacetic acid solution support a mechanism involving electrostatic ejection of pre-formed ions.

A new dynamics facility combining a storage ring with a synchronized free electron laser

Jefferson Laboratory currently operates a kilowatt average power, subpicosecond mid-infrared free electron laser as a user facility. We present plans to add an electron storage ring to this facility. Pulses of light from both sources will be synchronized at repetition rates up to 125 MHz to allow pump–probe dynamics experiments to be performed. We will present an outline of the new facility together with the operational parameters of the two sources. The new facility could be on line as a user facility in 2004.

Infrared laser desorption and ionization of polypeptides from a polyacrylamide gel

We observed direct desorption and ionization of angiotensin II and bovine insulin from a frozen polyacrylamide gel without the addition of an exogenous matrix, using picosecond pulses from a tunable, mid-infrared free-electron laser tuned to strong absorption bands of the gel. At 5.7, 5.9, 6.1 and 6.3 microm we were able to desorb and ionize both analyte molecules, with the strongest analyte signal generated at 5.9 microm. However, no analyte signal was observed at 5.5 microm. Consistent with a previous report, we did not observe ions of either polypeptide at 2.9 microm, in spite of strong overall absorption. We discuss the implications of this wavelength-dependent ionization, including possible ablation mechanisms and energy partitioning between competing vibrational modes.

Status of the FEL-SUT Project

IR FEL Research Center was established in the Noda Campus of the Science University of Tokyo on April 1, 1999, as a FEL user facility dedicated for the application of infrared free electron laser. The first observation of lasing emission from the mid-infrared free electron laser (MIR-FEL) was done on July 6, 2000 and the saturation emission was observed on September 27, 2000. The MIR-FEL machine is stably providing light for various application experiments. The infrared light from MIR-FEL is tunable over the wavelength region from 5 to 16 microns, the time width of its micro-pulse being about 2 pico-seconds with peak power of a few MW. Another FEL machine (FIR-FEL), which covers the wavelength region of 300-1000 microns, is now under construction. We report here the present status of the FEL machines, beam lines and experimental apparatus installed in the IR FEL Research Center.

Dissociation of cholesterol ester induced by the thermal effect of mid-infrared free electron laser

Cholesteryl ester is a compound of cholesterol and fatty acid, and is highly accumulated in arteriosclerosis regions and gallstones. We have studied irradiation effects of mid-infrared free electron laser (MIR-FEL) on cholesterol ester. In order to search optimum laser conditions for efficient removal of cholesterol ester, we tuned the FEL wavelengths to 5.75 (ester bond) and 6.82 µm (methylene bond), and irradiated cholesteryl oleate, a kind of cholesterol esters. The average power density was varied in the range of 1-10 W/cm2. Each irradiated sample was analyzed using a mass spectrometer to examine products after irradiation and obtain efficiencies of ester dissociation. The results indicate that (1) ester bond of cholesteryl oleate was dissociated to generate cholesterol and oleic acid, (2) irradiation products and dissociation efficiency of ester bond were similar regardless of the vibration modes which absorbs irradiated wavelength of MIR-FEL, and (3) the laser induced effects were considered to be thermal effects without accompanying thermal diffusion.

Infrared Multi-Photon Dissociation of SiF3I by Co-Irradiation with FEL and TEA-CO2 Laser

IR multi-photon dissociation of SiF3I in gaseous phase (pure SiF3I at 5 torr with natural abundance of Si isotopes) was studied by use of the mid-infrared free electron laser (MIR-FEL) of the IR FEL Research Center of the Tokyo University of Science. The following three kinds of experiment were carried out: irradiation with FEL only, irradiation with TEA-CO2 laser and co-irradiation with FEL and TEA-CO2 laser. Upon irradiating SiF3I with a strong light in the 10 µm spectral region, SiF3I was partially dissociated. The dissociation rate was found to be markedly enhanced by the co-irradiation with TEA-CO2 laser and FEL. The experimental results showed that the dissociation reaction SiF3I →SiF3 + I was induced by the multi-photon process, but isotope selectivity could not be found because SiF3 radical thus formed further reacted to form SiF4, SiF3I and SiF2I2.

Wavelength dependency of the optical properties of water in the bending vibrational band with photo-acoustic measurement

Laser-induced acoustic waves have been successfully used for the measurements of dynamic optical properties. We estimated the optical properties of water in the O-H bending vibrational band using the acoustic waves emitted from water irradiated by a tunable mid-infrared Free Electron Laser (MIR-FEL). From these observations, the following results were obtained. (1) The absorption spectrum of water from photo-acoustic measurements was in agreement with that obtained by the FT-IR measurement at room temperature. (2) There was a slight trend in the absorption spectrum below ∼6.1 µm to shift toward longer wavelengths, which is consistent with the previous report on the dynamic optical properties. This technique using longer MIR pulsed-lasers can be used to elucidate the dynamic optical properties of the tissues that depend on the temperature and composition during laser irradiation.

A Study of Tooth Structure Irradiated with IR-FEL

The effects of the irradiation with strong mid-infrared beam of FEL on teeth were studied by use of the mid-infrared free electron laser (MIR-FEL) of the IR FEL Research Center of the Tokyo University of Science, aiming to determine an effective and safe wavelength for fortifying tooth structure. Black discoloration was observed in the irradiated area for all specimens, but more clearly in the cases of softened dentin. SEM images showed an ablated cavity surrounded by dissolved apatite that resembled lava is formed. The irradiation experiment was done at the wavelengths of 8.8, 9.4 and 10.6 µm. The depth of the enamel cavity created the irradiation was found to be deeper depending on the wavelength in the order: 8.4, 10.6 and 9.5 µm. The 9.5 µm FEL beam selectively ablated enamel and dentin surfaces, even if it was softened. These results indicate that the 8.5 µm beam will cause only a mild damage to the enamel structure. Thus 8.5 µm FEL beam may be suitable for increasing the acid resistance of enamel, alongside the simultaneous application of fluoride.

Status of the Beijing IR Free Electron Laser facilities

Beijing free electron laser (BFEL) is a Compton type mid-infrared FEL facility. By using a thermionic cathode RF gun as an injector, 30 MeV s-band RF linac and two wiggler-optical cavity beam lines generate mid- and far-infrared radiation in the wavelength range of 5-50 µm. BFEL facility possesses the conditions for a user's facility. The running is stable, intensity fluctuation of laser is small, and wavelength adjustment is flexible. The stability test showed that the pulse energy fluctuation is about 1% within 30 minutes, and wavelength fluctuation is less than 0.1%. In this year, the lasing time used for users has reached 1000 hours. More than 250 samples have been studied and many application items have been concerned. Five user's stations will be established. Among them, two key experimental stations; FEL spectrum analysis station, and FEL steady state analysis station, have been constructed. For the purpose of user's applications, special equipments have been provided. Some experimental results of the application items are also presented.

Thin-film deposition method assisted by mid-infrared-FEL

We propose the novel application of the mid-infrared (MIR) FEL to the thin-film fabrication process. During the application, a substrate on which a thin film is being fabricated by a conventional method is simultaneously irradiated by the MIR FEL. The MIR FEL induces the fabricated molecules into the excited state of the stretching vibration energy, when the photon energy of the MIR FEL corresponds to one of the molecules. Therefore, the method can assist the thin-film fabrication quasi-independent of the substrate temperature. The method has the advantages of application on a temperature sensitive substrate and selective fabrication due to the tunable wavelength of the MIR FEL. In order to realize the method, we developed two thin film fabrication devices; an MIR FEL assisted RF sputtering device and an MIR FEL assisted laser ablation deposition device. For the method, the intensity of the assisted MIR FEL is an important problem. Thus the cross-section of the MIR FEL intensity profile is shown and the propagation discussed.