Introduction
The Center for Ultrafast Lasers (CLUR) was founded by approval of the Complutense University of Madrid (UCM) Social Council on September 26th, 2013, and it is one of the Research Infrastructures of the University. This Center started at the beginning of the 1990’s as a Service for Multiphoton Spectroscopy within the Center for Spectroscopy of the University, with the aim of offering to the university and scientific community of a series of techniques based on high power pulsed lasers in combination with multiphoton ionization laser spectroscopy and time-of-flight mass spectrometry. Nowadays, as it will be described in detail below, the available techniques and instrumentation allow to carry out experiments and assays with temporal resolution in the scales of nanoseconds (10-9 seconds) and femtoseconds (10-15 seconds), in a variety of samples and systems in the three fundamental states of matter (gases, liquids, solids), by means of pump-probe laser techniques and laser spectroscopy (photoionization, photoelectron spectroscopy, fluorescence). In addition, the manipulation of materials (laser microfabrication, laser modification of materials, laser ablation) and the synthesis of new materials (femtosecond and nanosecond pulsed laser deposition of nanostructures) are possible with the available laser instrumentation.
Laser Multiphoton Ionization allows efficient ionization of atoms and molecules by means of high power laser radiation in the visible (VIS) and ultraviolet (UV) range. Ionization of atoms or molecules requires the absorption of electromagnetic radiation of enough energy to reach the ionization potential by absorption of one photon. This, generally, implies the use of vacuum ultraviolet (VUV) radiation. However, if irradiance is high enough, multiphoton processes (multiphoton absorption) in atom or molecules are possible, yielding ionization and/or molecular fragmentation using VIS or UV laser radiation. If wavelength tuneability of the laser radiation is available, then Resonance Enhanced Multiphoton Ionization (REMPI) is possible. In order to measure the ions of different masses produced by the interaction of the molecules and the laser pulses, the Time-of-Flight Mass Spectrometry (TOFMS) technique is employed. In this mass spectrometry, mass separation of the ions is achieved by resolving the arrival times of the different ions to a detector in a time-of-flight tube, since those ions with larger mass will spend longer in reaching the detector than those of lower mass.
Laser Multiphoton Ionization allows efficient ionization of atoms and molecules by means of high power laser radiation in the visible (VIS) and ultraviolet (UV) range. Ionization of atoms or molecules requires the absorption of electromagnetic radiation of enough energy to reach the ionization potential by absorption of one photon. This, generally, implies the use of vacuum ultraviolet (VUV) radiation. However, if irradiance is high enough, multiphoton processes (multiphoton absorption) in atom or molecules are possible, yielding ionization and/or molecular fragmentation using VIS or UV laser radiation. If wavelength tuneability of the laser radiation is available, then Resonance Enhanced Multiphoton Ionization (REMPI) is possible. In order to measure the ions of different masses produced by the interaction of the molecules and the laser pulses, the Time-of-Flight Mass Spectrometry (TOFMS) technique is employed. In this mass spectrometry, mass separation of the ions is achieved by resolving the arrival times of the different ions to a detector in a time-of-flight tube, since those ions with larger mass will spend longer in reaching the detector than those of lower mass.
The REMPI and TOFMS techniques are specially suited for structural characterization of organic, inorganic and organometalic compounds, and the identification and detection of traces in samples. Combination of these techniques with Gas Chromatography (GC) and laser ablation and laser desorption allow for qualitative and quantitative analyses of volatile and non-volatile compounds in solid, liquid or gas samples. Additionally, given their character as laser spectroscopy techniques, it is possible to measure high resolution electronic spectra in the UV and VUV for a given mass ion along with fragmentation patterns as a function of laser wavelength. The main advantages of these techniques with respect to other analytical techniques are: high specificity, since it is possible to find a given wavelength at which a compound in a sample absorbs and ionizes efficiently; high sensitivity, due to the high efficiency of laser ionization by REMPI, much higher than for other conventional ionization methods. The measurement of fragmentation patterns at different wavelengths and/or laser powers provides qualitative and quantitative information about the molecule(s) of interest, along with structural information and ionization potentials.
Nowadays, the REMPI and TOFMS techniques are used in combination with ion imaging techniques: velocity map imaging (VMI) and slice imaging (SI), to study the dynamics of chemical processes, such as photodissociation reactions or photon initiated chemical reactions.
From the very beginning, a Nanosecond Laser System, made of two Nd:YAG lasers and two dye lasers including second harmonic generation, is available. With this nanosecond laser system, upgraded in 2009, tuneable high-power pulsed nanosecond lases radiation is available from 199 nm up to the near infrarred. With these two tuneable laser beams, it is possible to carry out pump-probe or double-resonance experiments in combination with TOFMS and ion imaging.
In 2004, a Femtosecond Laser System was installed and since then the Center was called Service for Multiphoton and Femtosecond Spectroscopy within the Center for Spectroscopy. This femtosecond laser system yielded a train of femtosecond laser pulses at a repetition rate of 1 kHz and pulsewidth of 80 fs (1 fs = 10-15 s) centered at 800 nm and 1 mJ per pulse. A single-shot autocorrelator and second, third and fourth hamonic generation (400 nm, 266 nm and 200 nm) units were available along with two optical parametric amplifiers (OPA) to generate femtosecond tuneable radiation from 235 nm in the UV up to 3000 nm in the IR. This femtosecond laser system was upgraded in 2009 to femtosecond laser pulses better than 35 fs and 3.5 mJ per pulse. An Dazzler acousto-optic modulator was installed after the oscillator to optimize the laser pulses. Pulse diagnostics are carried out by the FROG and Dazzcope techniques. In addition, a spatial light modulator (SLM) is available for pulse shaping.
In 2013, a second Femtosecond Laser System generating 80 fs pulses and 1 mJ per pulse was installed. This laser was coupled to a femtosecond time-resolved Fluorescence Up-conversion equipment that allows the measurement of lifetimes for liquid or solid samples from few hundred femtoseconds up to several nanoseconds.
The availability of femtosecond lasers in the laboratory has changed completely the kind of experiments and assays that are now possible and thus the center is called since then the Center for Ultrafast Lasers (CLUR). Using these laser technologies, it is now possible to offer access to laser services for research at the frontier of Chemistry, Physics, Biology and Material Science in research fields involving ultrafast lasers to investigate phenomena at the temporal scale where they happen (Femtochemistry, Femtophysics, Femtobiology). Only with such an ultrashort time resolution it is possible to understand molecular change at the time scale where molecular processes occur, such as bond breaking and forming, molecular movements (vibration and rotation) or energy transfer, proton transfer and electron transfer processes of interest in Chemistry and Biology. The availability of ultraintense laser pulses makes it possible to study matter under strong electromagnetic fields where the processes of interest at a molecular level are dissociative ionization, Coulomb explosion and high order harmonic generation. In addition, the use of ultrafast laser pulses allows to have a photonic tool of high capabilities for materials microfabrication and nanostructured materials and thin film synthesis and modification. The possibility of pulse shaping is also relevant for the field of quantum control of physical and chemical processes and material science.
The availability of femtosecond lasers in the laboratory has changed completely the kind of experiments and assays that are now possible and thus the center is called since then the Center for Ultrafast Lasers (CLUR). Using these laser technologies, it is now possible to offer access to laser services for research at the frontier of Chemistry, Physics, Biology and Material Science in research fields involving ultrafast lasers to investigate phenomena at the temporal scale where they happen (Femtochemistry, Femtophysics, Femtobiology). Only with such an ultrashort time resolution it is possible to understand molecular change at the time scale where molecular processes occur, such as bond breaking and forming, molecular movements (vibration and rotation) or energy transfer, proton transfer and electron transfer processes of interest in Chemistry and Biology. The availability of ultraintense laser pulses makes it possible to study matter under strong electromagnetic fields where the processes of interest at a molecular level are dissociative ionization, Coulomb explosion and high order harmonic generation. In addition, the use of ultrafast laser pulses allows to have a photonic tool of high capabilities for materials microfabrication and nanostructured materials and thin film synthesis and modification. The possibility of pulse shaping is also relevant for the field of quantum control of physical and chemical processes and material science.
CLUR offers the possibility of custom made experiments and assays. The different nanosecond and femtosecond lasers available in combination with the additional instrumentation in the lab (molecular beams, TOFMS, ion and photoelectron imaging, time-resolved fluorescence, optics and optomechanics) and the availability of dedicated experts at CLUR allow for custom requested experimental setups and assays involving laser pulses. This way, CLUR is a unique laser installation offering access to researchers from many different areas of research in research projects involving instrumental developments.
More details about the kind of experiments and assays that can be carried out at CLUR are found in Red.escubre (in Spanish).
CLUR and the Spanish Scientific Infrastructure (ICTS) Centro de Láseres Pulsados Ultracortos Ultraintensos (CLPU) at Salamanca share a collaboration agreement. This agreement is of great importance for CLUR to offer complementary laser services to an even wider scientific communitiy at a National and International level.
More details about the kind of experiments and assays that can be carried out at CLUR are found in Red.escubre (in Spanish).
CLUR and the Spanish Scientific Infrastructure (ICTS) Centro de Láseres Pulsados Ultracortos Ultraintensos (CLPU) at Salamanca share a collaboration agreement. This agreement is of great importance for CLUR to offer complementary laser services to an even wider scientific communitiy at a National and International level.