FEL Users Workshop

FRAIS01 Advances in the Physical Understanding of Laser Surgery at 6.45 microns
Michael Shane Hutson (Vanderbilt/DPA, Nashville - Tennessee), Glenn Edwards (DU/FEL, Durham, North Carolina)

We previously presented a model that attributes the wavelength-dependence of FEL tissue ablation to partitioning of absorbed energy between protein and saline. This energy-partitioning subsequently influences the competition between protein denaturation and saline vaporization. The original model approximated cornea as a 1D laminar material with a 50:50 saline-to-protein volume ratio. We have now refined the microscopic geometry of the model in two important ways: (1) cornea is represented as a saline bath interpenetrated by a 2D hexagonal array of protein fibrils; (2) the volume ratio is matched to the measured value, 85:15. With this volume fraction, the specific absorption coefficient for protein is much larger than previously reported. Thus, the 2D model magnifies the differences between wavelengths that target protein, as opposed to saline. We will discuss: (1) the consistency of this model with previous, seemingly conflicting, experimental data; (2) predictions of the model, with a particular emphasis on the role of laser intensity; and (3) the experiments needed to test these predictions.

THCIS01 Proposals for Pump-Probe Experiments in the Gas Phase using the TTF2-FEL
Michael Meyer (LURE, Orsay)

Many processes induced by the interaction of XUV light with atoms and molecules take place on a very short time scale. The temporal width of the soft X-Ray FEL pulses (100-300 fs) and of the synchronized, tunable optical laser (150 fs) will therefore be ideally suited to gain an insight into the dynamics of these processes. A first series of proposed experiments will serve to characterize the FEL pulses themselves, in particular the intensity, frequency and time structure of the individual pulses by using a cross correlation technique between the XUV photons and a strong infrared pulse. Depending on the final characteristics of the FEL with respect to photon energy range and tunability, these two-photon pump-probe experiments will be extended to further studies, like the investigation of resonances, which are only accessible by a two-photon excitation, the coupling of autoionization states by a strong laser field, which induces drastic changes in the resonance profiles, the wavepacket formation of higher Rydberg states, and the coherent population of excited states by fast dissociation, which will result in the observation of quantum beats on the decay curve of excited fragments.

FRAOS03 Picked FEL Micro Pulse for Nano-Second Interaction with Bio-Molecule
Sachiko Suzuki, Kunio Awazu, Katsonuri Ishii, T. Kanai, Y. Naito (OU-iFEL, Hirakata, Osaka)

Laser pulse duration is a very important parameter to determine the threshold between thermal and nonthermal effects in laser surgery of biomedical tissue. Free Electron Laser (FEL) at Osaka University, Japan, has a pulse structure in which a macropulse (pulse width : 15μs) consists of equally separated micropulses, whose width and interval are ~5ps and 44.8ns, respectively. Precise control of micropulse train may establish fast optic processes because thermal relaxation time in the tissue is about 1us. A pulse-picking system was designed in order to extract single or a few micropulses from an entire macropulse using an acousto-optic modulator (AOM) in which the light path can be temporally diffracted by an external gate signal. An extracted micropulse train was monitored by a mercury-cadmium-telluride (MCT) photodetector with ~1ns response time and recorded on digital oscilloscope. A single micropulse was extracted as a result of adjusting duration of the RF wave to 50 ns which is nearly equal to the interval of micropulse. Investigation of a fast interaction between the FEL and a tissue using this system is expected.

FRAOS04 Coherent Protein Dynamics Explored at FELIX
Robert Austin (PU, Princeton, New Jersey), Britta Redlich, Lex van der Meer (FOM Rijnhuizen, Nieuwegein), Aihua Xie (OKSU-Phy, Stillwater - Oklahoma)

We have discovered that there exists a very narrow (less than 0.02 microns) wide resonance in the amide I band of myoglobin and photoactive yellow protein that can be driven to greater than 30% saturation using very narrow linewidth pump-probe spectroscopy at FELIX. The extraordinary narrowness of this transition and the extraordinary ease of saturation inplies that this band is highly anharmonic and decoupled from the other oscillators in the amide I band. We will present detailed measurments on this discovery and implications for energy flow in proteins.

THBOS02 Preparation Femtosecond Laser Prevention for the Cold-Worked Stress Corrosion Crackings on Reactor Grade Low Carbon Stainless Steel
Eisuke John Minehara, Akihiko Nisimura (JAERI/FEL, Ibaraki-ken), Takashi Tsukada (JAERI, Ibaraki-ken)

We report here that the femtosecond lasers like low average power Ti:Sapphire lasers, the JAERI high average power free-electron laser and others could peel off and remove two stress corrosion cracking (SCC) origins of the cold-worked and the cracking susceptible material, and residual tensile stress in hardened and stretched surface of low-carbon stainless steel cubic samples for nuclear reactor internals as a proof of principle experiment except for the third origin of corrosive environment. Because a 143 °C and 43% MgCl2 hot solution SCC test was performed for the samples to simulate the cold-worked SCC phenomena of the internals to show no crack at the laser-peered off strip on the cold-worked side and ten-thousands of cracks at the non-peeled off on the same side, it has been successfully demonstrated that the femtosecond lasers could clearly remove the two SCC origins and could resultantly prevent the cold-worked SCC.

THBOS03 THz Imaging by a Wide-band Compact FEL
Young Uk Jeong, Hyuk Jin Cha, Byung Cheol Lee, Seong Hee Park (KAERI, Daejon), Grigori M. Kazakevitch (BINP, Novosibirsk)

We have developed a laboratory-scale users facility with a compact THz FEL. The FEL operates in the wide wavelength range of 100–1200 μm, which corresponds to 0.3-3 THz. THz radiation from the FEL shows well collimated Gaussian spatial distribution and narrow spectral width of 0.3 μm, which is Fourier transform limited by the estimated pulse duration of 20 ps. The main application of the FEL is THz imaging for bio-medical researches. We are developing THz imaging techniques by 2-D scanning, single pulse capturing with the electro-optic method, and 3-D holography. High power, coherent, and pulsed feature of the FEL radiation is expected to show much better performance in advanced THz imaging of 3-D tomography by comparing with incoherent and weak THz sources. By controlling the optical delay between reference beam and scattered light from an object, we can get its 3-D tomography by the holograms. The coherent and pulse length of the FEL beam is measured to be 3-6 mm. In this paper we will show and discuss the main results of THz imaging with the different methods by using the KAERI compact FEL.

THBOS04 The Present Applications of IR FEL at Peking University
Limin Yang, Jia'er Chen, Kui Zhao (PKU/IHIP, Beijing), MingKai Wang (Chinese Academy of Sciences, Beijing), Yunlan Su, Jinguang Wu, Yizhuang Xu (College of Chemistry and Molecular Engineering, Beijing)

In this study the sections of human tissues were treated under 9.5 μm FEL in the BFEL based on the vibrational spectroscopic investigation that significant differences occur between normal and malignant tissues. Under the defocus condition, the burning of tissue section at some part while other part remains unchanged, suggesting that the FEL can selectively destroy some part of tissue. Vibrational spectroscopic and microscopic methods have shown that the FEL can induce decomposition of malignant tissues. The application of FEL whose wavelength is on the characteristic bands of malignant tissues may provide a new method to kill cancer cells with higher selectivity. For understanding the interactions between FEL and biological tissues, structure changes of substances under irradiation by FEL of 9.414 μm and 6.228 μm were measured using FTIR spectroscopy. The samples include ATP, ADP, AMP, and D-ribose, etc. The FTIR spectra of the molecules before and after irradiation of FEL indicate molecular structure variations of the samples after irradiation of FEL, especially the rearrangement of their hydrogen bond networks, which may be caused by multiple photons process induced by FEL.

THCOS02 Interaction of Intense Ultrashort XUV Pulses with Different Solids – Results from the Tesla Test Facility FEL Phase I
Jacek Krzywinski, Marek Jurek, Dorota Klinger, Jerzy Pelka, Andrzej Wawro (IP PAS, Warsaw), Marcin Sikora (AGH University of Science and Technology, Krakow), Evgeny L. Saldin, Evgeny A. Schneidmiller, Barbara Steeg, Rolf Treusch, Mikhail V. Yurkov (DESY, Hamburg), Michal Bittner, Dagmar Chvostova, Libor Juha, Vit Letal, Vladimir Vorlicek (FZU, Prague), Andrzej Andrejczuk, Henryk Reniewicz (University of Bialystok, Bialystok), Ryszard Sobierajski (Warsaw University of Technology, Warsaw), Anna Kauch (Warsaw University, Warsaw)

Desorption, ablation, and plasma formation have been studied for a large variety of materials (insulators, semiconductors, and metals). Damaged surfaces have been investigated using light, electron, and atomic force microscopy. Short-wavelength ablation was very efficient and clean when proper irradiation conditions were chosen. The edges of craters were sharp, and the area around the craters was clean. A distinct difference in the behavior of conducting materials and insulators was observed. In the case of insulators the morphology of the irradiated surface and the crater depth hardly depended on the beam intensity. In contrast, the irradiated silicon surface becomes very rough when the intensity exceeds the damage threshold. At high intensities multiple charged ions were registered. Kinetic energy of the ions increases with charge state and reaches keV range for highly-charged ions. Again, a clear difference between insulators and conducting material was observed. High charge states and energetic ions were typical for conductors and semiconductors. Only single ions states and low energetic ions (~50 eV) were detected for insulators for all irradiation conditions.

THPOS05 Exploring the Spatial Resolution of the Photothermal Beam Deflection Technique in the Infrared Region
Wolfgang Seidel, Harald Foerstendorf (FZR, Dresden), François Glotin, Jean Michel Ortega, Rui Prazeres (LURE, Orsay)

In photothermal beam deflection spectroscopy (PTBD) generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry. Recent results of PTBD experiments are presented with a high spatial resolution which is near the diffraction limit of the infrared pump beam (CLIO-FEL). We investigated germanium substrates showing restricted O+-doped regions with an infrared absorption line at a wavelength around 11.6 microns. The spatial resolution was obtained by strongly focusing the probe beam (i.e. a HeNe laser) on a sufficiently small spot. The strong divergence makes it necessary to refocus the probe beam in front of the position detector. The influence of the focusing elements on spatial resolution and signal-to-noise ratio is discussed. In future studies we expect an enhanced spatial resolution due to an extreme focusing of the probe beam leading to a highly sensitive technique for detection of sorbed species on surfaces in the far infrared region.

THPOS08 Experiments on the Synchronization of an Ultrafast Cr:LiSAF Laser with the ELETTRA Storage Ring and FEL Pulses
Mario Ferianis, Miltcho B. Danailov, Giovanni De Ninno, Bruno Diviacco, Mauro Trovò (Elettra, Basovizza, Trieste), Marcello Coreno (CNR-IMIP, Basovizza (TS)), Gamal Elsayed Afifi (NILES, Cairo)

The techniques for synchronizing ultrafast lasers to external radio frequency reference sources are well established and characterized in the literature. However, data lack on the minimum light-to-light jitter which can be achieved in different synchrotron operation modes when an external laser is locked to the storage ring master clock. Here we present first results for the synchronization of an ultrafast Cr:LiSAF laser with electromagnetic radiation coming from the Elettra storage ring in four bunch and multi-bunch mode. In addition, data on the synchronization of the same laser with the Elettra FEL pulses, both in free running and Q-switching regime, are reported. In our experiments, laser-to-RF locking was continuously monitored using a built-in phase detection. The laser light to storage ring light locking was characterized by simultaneous acquisition of two/three pulse trains by a streak camera. In addition, pulse jitter was determined by processing of the signal of fast photodiodes monitoring the different light beams.

THPOS14 Laser Compton Scattering Gamma Ray Induced Photo-Trasmutation
Dazhi Li, Kazo Imasaki (ILT, 2-6 Yamada-oka, Suita, Osaka), S. Amano, S. Miyamoyo, T. Mochizuki (LASTI, Hyogo)

High brightness beams of gamma rays produced with laser Compton scattering have the potential to realize photo-transmutation through (γ,n) reaction, implying an efficient method to dispose long-lived fission products. Preliminary investigations have been carried out in understanding the feasibility of development of a transmutation facility to repose nuclear waste. A laser Compton scattering experimental setup based on a storage ring started to generate gamma-ray beams for studying the coupling of gamma photons and nuclear giant resonance. This paper demonstrates the dependency of nuclear transmutation efficiency on target dimensions and gamma ray features. 197Au sample was adopted in our experiment, and experimental results correspond to the theoretical estimations.

THPOS18 Development of a Pump-Probe System using a Non-Coated ZnSe Beam Splitter Cube for an MIR-FEL
Manabu Heya, Kunio Awazu, Hiroshi Horiike, Katsonuri Ishii, Sachiko Suzuki (OU-iFEL, Hirakata, Osaka)

A pump-probe technique is essential for a proper understanding of laser interaction with tissue and material. Our pump-probe system divides the incident mid-infrared Free Electron Laser (MIR-FEL) into two beams with equal intensity, and crosses simultaneously the two incoming beams at the same position. One is for a pump beam, another is for a probe beam. Time-resolved absorption spectroscopy involving this technique gives us information on the vibrational dynamics of molecules. We have developed this system for an MIR-FEL using a non-coating ZnSe beam splitter cube. The beam splitter cube is composed of two ZnSe prisms in the shape like a trapezoid. The two pulses with equal intensity are generated due to Fresnel reflection and transmission at the boundary between two prisms, then are reflected due to total reflection at other side boundaries between each prism and air, and illuminate simultaneously the same spot. We have conducted a proof-of-concept of experiment of this system using an MIR-FEL. We showed that this system is applicable for a broad waveband (6-11 μm). Thus, we proved that this system without complicated optical alignment is useful for absorption spectroscopy.

THPOS19 Medical Application of Free Electron Laser Trasmittance using Hollow Optical Fiber
Sachiko Suzuki, Kunio Awazu, Katsonuri Ishii (OU-iFEL, Hirakata, Osaka)

Mid-infrared Free Electron Laser (FEL) is expected as new application for biomedical surgery. However, delivery of MIR-FEL into the body is difficult because the common glass optical fibers have strong absorption at MIR region. A good operational and flexible line for FEL is required at medical field. A Hollow optical fiber is developed for IR laser and high-power laser delivery. We evaluated the fiber for FEL transmission line. This fiber is coated with cyclic olefin polymer (COP) and silver thin film on the inside of glass capillary tube. It is 700 μm-bore and 1m in lengths. The fiber transmission loss of the measured wavelength region of 5.5 μm to 12 μm is less than 1dB/m when the fiber is straight and 1.2 dB/m when bent to radius of 20 cm. Additionally, the output beam profile and the pulse structure is not so different form incidence beam. In conclusion, the fiber is suitable for delivery of the FEL energy for applications in medical and laser surgery.

THPOS25 Modification of Hydroxyapatite Crystal Using IR Laser
Saburoh Satoh, A. Danjyo, M. Goto, W. Guan, N. Hayashi, S. Ihara, C. Yamabe, Y. Yamaguchi (Saga University, Saga)

The first application of laser technology to dentistry was for the removal of caries. However, reports of laser application on improvement of dental surface were emerged, much attention has been focused on the laser’s potential to enhance enamel’s hardness and resistance to acid. Most of the previous reports concentrated on the photo issue interaction. Few research has pursued the photochemical phenomenon occurred during laser irradiation on biological tissues. In order to find a creative method to remineralize the dissociating enamel and exposed coronal of dentine, the authors developed a novel procedure during laser irradiation. Slice of sound molar and artificial HAp pellet were irradiated separately, with CO2 laser under different laser parameters. Tow series of samples covered with saturation calcium ion solution were irradiated separately. To investigate the crystal morphology, XRD pattern were surveyed. The comparison of each cases show that the chemical coating affected the ablation process evidently though distinct XRD results were observed. After CO2 laser irradiation, the (002) reflection was increased significantly that indicates the crystal growth in c-axis.

THPOS26 Vibrational Excitation of Ammonia Molecules by FEL-SUT
Yoshihiro Ogi, Koichi Tsukiyama (TUS-Kagurazaka, Shinjuku, Tokyo)

Free Electron Laser at Tokyo University of Science (FEL-SUT) was employed for exciting single vibrational modes of ammonia molecules. FEL is tuned to 10.5 μm, corresponding to the X1A1' (ν2 = 1) ← (ν2 = 0) transition of NH3. The population of the vibrationally excited states is probed by the (2 + 1) resonance enhanced multiphoton ionization (REMPI) technique via the B 1E" Rydberg state. Maximum excitation efficiency of ν2 = 1 ← ν2 = 0 transition was about 50 %, which was estimated by taking account of Franck-Condon factors and the rotational line strengths. Rotational analyses of the spectra revealed that vibrational ladder climbing up to ν2 = 2 in NH3 was realized for the first time. Experimental results on ν4 vibrational excitation of NH3 and ND3 will be also reported.

THPOS30 Photo-Acoustic Spectroscopy with Infrared FEL
Masato Yasumoto, Hiroshi Ogawa, Norihiro Sei, Kawakatsu Yamada (AIST-PRI, Tsukuba, Ibaraki)

Photo-acoustic spectroscopy (PAS) is a sensitive technique for measuring small absorptions of samples. In an ordinary PAS a pulse laser is used as a light source for inducing photo-acoustic signals. In our novel PAS an infrared FEL is used as the light source. The infrared FEL is continuously tunable in the wavelength with a high repetition rate. Thus, the PAS with the infrared FEL can be applied in various samples compared with the ordinary PAS. We will show the feasibility of the novel PAS.