Showing papers in "Applied Physics B in 1997"

Ultrashort-pulse fiber ring lasers

Abstract: This paper reviews recent progress on ultrashort pulse generation with erbium-doped fiber ring lasers. The passive mode-locking technique of polarization additive pulse mode-locking (P-APM) is used to generate stable, self- starting, sub-500 fs pulses at the fundamental repetition rate from a unidirectional fiber ring laser operating in the soliton regime. Saturation of the APM, spectral sideband genera- tion, and intracavity filtering are discussed. Harmonic mode- locking of fiber ring lasers with soliton pulse compression is addressed, and stability regions for the solitons are mapped and compared with theoretical predictions. The stretched- pulse laser, which incorporates segments of positive- and negative-dispersion fiber into the P-APM fiber ring, gen- erates shorter (sub-100 fs) pulses with broader bandwidths (> 65 nm) and higher pulse energies (up to 2: 7n J). We dis- cuss optimization of the net dispersion of the stretched-pulse laser, use of the APM rejection port as the laser output port, and frequency doubling for amplifier seed applications. We also review the analytical theory of the stretched-pulse laser as well as discuss the excellent noise characteristics of both the soliton and stretched-pulse lasers.

Femtosecond pulse shaping by an evolutionary algorithm with feedback

Abstract: We report on computer controlled compression of femtosecond laser pulses using a programmable liquid crys- tal spatial light modulator which is feedback-controlled by an evolutionary algorithm. This algorithm generates the opti- mal laser field on the basis of feedback from the experiment by optimizing the laser pulse iteratively. Without knowledge of the (chirped) input pulses, the experimental signal (second harmonic light=SHG) is maximized by the algorithm, thus re- sulting in fully compressed pulses. This method only makes use of the experiment's response (SHG signal) on the formed pulses. No other parameters need to be considered. This ap- proach leads to many experimental applications in all fields of optics and ultrafast spectroscopy where particularly shaped pulses are advantageous.

The ion trap quantum information processor

Abstract: An introductory review of the linear ion trap is given, with particular regard to its use for quantum information processing. The discussion aims to bring together ideas from information theory and experimental ion trapping, to provide a resource to workers unfamiliar with one or the other of these subjects. It is shown that information theory provides valuable concepts for the experimental use of ion traps, especially error correction, and conversely the ion trap provides a valuable link between information theory and physics, with attendant physical insights. Example parameters are given for the case of calcium ions. Passive stabilisation will allow about 200 computing operations on 10 ions; with error correction this can be greatly extended.

CW laser performance of Yb and Er,Yb doped tungstates

Abstract: Room temperature cw laser action of Yb3+-doped KY(WO4)2 and KGd(WO4)2 crystals at 1.025 μm and Er, Yb : KY(WO4)2 at 1.54 μm has been demonstrated under pumping by both Ti-sapphire laser and InGaAs laser diodes. A slope efficiency of Yb-lasers up to 78% has been obtained.

Light-induced charge transport processes in photorefractive crystals II: Materials

Abstract: , LiTaO3, BaTiO3, Ba1-xSrxTiO3 (\(\), BST), Ba1-xCaxTiO3 (\(\), BCT), KNbO3, KTa1-xNbxO3 (\(\), KTN), Sr1-xBaxNb2O6 (\(\), SBN) and Bi12(Si,Ti,Ge)O20 (BSO, BTO, BGO) are discussed. Utilizing the knowledge on the charge transport processes, consequences for applications are deduced; improved techniques for nondestructive readout of holograms with light of the recording wavelength are described.

A novel-high energy pulse compression system: generation of multigigawatt sub-5-fs pulses

Abstract: Powerful techniques for spectral broadening and ultrabroadband dispersion control, which allow the compression of high-energy femtosecond pulses to a duration of a few optical cycles, are presented. Spectral broadening by propagation along hollow-core fused silica fiber filled with atomic and molecular gases is studied under two excitation regimes with high-energy input pulses of 140 fs and 20 fs duration respectively. Conditions for optimum pulse compression are outlined considering the role of self-phase modulation and gas dispersion in the two regimes. With 20 fs input pulses and under optimum compression conditions we demonstrate a pulse shortening down to 4.5 fs with output energy up to 70 μJ using a high-throughput prism-chirped-mirror delay line. These pulses are the shortest generated to date at multigigawatt peak power. PACS: 42.65.Re; 42.65.Vh Ultrashort-pulse lasers are the most important experimental tools for investigating fast-evolving atomic and molecular dynamics in physics, chemistry, and biology. In the last few years, great technological advances have been made in the field of ultrafast pulse generation. New mode-locking techniques such as additive-pulse mode-locking and Kerr-lens mode-locking have been successfully used for femtosecond pulse generation from a wide range of solid-state laser oscillators [1]. Using chirped mirrors [2] for intracavity dispersion control, pulses down to 7.5 fs have been directly generated by a Kerr-lens mode-locked Ti:sapphire oscillator [3] and, more recently, 6.5-fs pulses have been obtained using broadband semiconductor saturable absorbers for self-starting [4]. Ti:sapphire amplifiers seeded by femtosecond laser oscillators can now generate pulses of 20–30 fs with gigawatt [5, 6] or terawatt [7–9] peak power at repetition rates in the kHz and 10 Hz regimes, respectively. Ultrashort pulses can also be generated by extracavity compression techniques, in which the pulses are spectrally broadened upon propagation in a suitable nonlinear waveguide and subsequently compressed in a carefully designed optical dispersive delay line. Spectral broadening of laser pulses by self-phase modulation (SPM) in a single-mode optical fiber is a well-established technique: pulses down to 6 fs were obtained in 1987 from 50-fs pulses from a mode-locked dye laser [10]. More recently 13-fs pulses from a cavity-dumped Ti:sapphire laser were compressed to 5 fs with the same technique [11]. However, the use of single-mode fibers limits the pulse energy to a few nanojoules. A powerful pulse compression technique based on spectral broadening in an hollow fiber filled with noble gases has demonstrated the capability of handling highenergy pulses (sub-mJ range) [12]. This technique presents the advantages of a guiding element with a large diameter mode and of a fast nonlinear medium with high threshold for multiphoton ionization. New concepts in the construction of dispersive delay lines have been applied in the development of specially designed chirped mirrors for fine control of cubic and quartic phase dispersion terms over a large spectral bandwidth [3]. The implementation of the hollow-fiber technique using 20-fs seed pulses from a Ti:sapphire system [5] and a high-throughput broadband dispersive delay line consisting of prisms and chirped mirrors has recently permitted the generation of multigigawatt sub-5 fs pulses [13]. In this paper we present a comprehensive analysis of compression experiments with high-energy femtosecond pulses performed using gas-filled hollow fibers. Spectral broadenings obtained in different gases are compared for 140-fs and 20-fs input pulses generated by Ti:sapphire laser systems, and the optimum conditions for pulse compression are outlined considering the role of SPM and gas dispersion. A new ultrabroadband prism-chirped-mirror dispersive delay line, characterized by a high throughput and dispersion control up to the fourth order, is described in detail. The paper is organized as follows. In Sect. 1 we provide a description of hollow fiber modes and discuss the major advantages of this device compared to optical fibers. Sect. 2 reports on typical spectral broadenings achieved under different excitation conditions. In Sect. 3 we report on the characteristics of the prism-chirped-mirror compressor and discuss the experimental results obtained with 20-fs input pulses. Under optimum compression conditions we show a pulse shortening down to 4.5 fs with output energy up to 70 μJ. These pulses are the

All-solid-state cavity-dumped sub-5-fs laser

Abstract: We discuss in detail a compact all-solid-state laser delivering sub-5-fs, 2-MW pulses at repetition rates up to 1 MHz. The shortest pulse generated thus far measures only 4.6 fs. The laser system employed is based on a cavity-dumped Ti:sapphire oscillator whose output is chirped in a single-mode fiber. The resulting white-light continuum is compressed in a novel high-throughput prism chirped-mirror Gires–Tournois interferometer pulse compressor. The temporal and spectral phase of the sub-5-fs pulses are deduced from the collinear fringe-resolved autocorrelation and optical spectrum. The derived pulse shape agrees well with the one retrieved from the measured group delay of the continuum and calculated characteristics of the pulse compressor.

Theory and design of chirped dielectric laser mirrors

Abstract: Chirped dielectric laser mirrors offer a general solution for broadband feedback and dispersion control in femtosecond laser systems. Chirped mirrors developed for modelocked solid-state lasers, femtosecond parametric oscillators, chirped pulse amplification systems and pulse compressors are introduced. Basic theoretical and design considerations are also presented. PACS: 42.15.Eq; 42.25.Bs; 42.40Pa; 42.60.Da; 42.65.k; 42.79Bh; 42.80.V One of the main trends of laser physics today is ultrafast laser technology. Recent research on high-power semiconductor laser diodes and solid-state laser materials with a broad fluorescence emission band has paved the way for compact, reliable, broadly tunable all-solid-state continuous wave (cw), picosecond (ps) and femtosecond (fs) pulse laser sources. One approach is based on Ti:sapphire ( Ti:S) [1], which can be efficiently pumped by the frequency-doubled output of AlGaAs diode-pumped neodymium lasers. Alternatively, the direct diode pumping of colquiriite laser-active materials such asLiCaAlF6:Cr3+ (Cr:LiCAF) [2], LiSrAlF6:Cr3+ (Cr:LiSAF) [3], and LiSrGaF6:Cr3+ (Cr:LiSGAF) [4] became feasible by the use of enhanced mode-matching schemes [5] or AlGaInPsemiconductor lasers with “improved” beam quality operating near 670 nm[6]. The latter approach might offer greater simplicity, efficiency, compactness, and cost effectiveness. The importance of these features for wideranging applications needs no explanation. These advances in laser technology offered the possibility of constructing laser oscillators generating optical pulses in the sub20-fs regime by using different mode-locking techniques such as self-mode-locking of the laser [7]. Because of the dominant role of soliton-like pulse shaping in ultrashort-pulse solid-state lasers [8], femtosecond-pulse generation relies on net negative, i.e. anomalous, intracavity group-delay dispersion (GDD). Solid-state gain media always introduce a certain amount of frequency-dependent positive (normal) dispersion in the cavity, which must be balanced as well. Until recently, Brewster-angled prism pairs [9] built into the laser cavity were the only low-loss sources of broadband negative GDD. In prism-pair-controlled broadband lasers, a major limitation to ultrashort-pulse generation originates from the variation of the intracavity GDD with wavelength. The principal source of this higher-order dispersion, however, was found to be the prism pair [10, 11]. If the lasers are operated in the vicinity of zero GDD, the spectra of sub20-fs pulses from prism-pair-controlled oscillators are asymmetric with a broad shoulder [10] or are double peaked [8, 11] depending on whether the soliton-like pulses are, respectively, thirdor fourth-order dispersion limited. This deviation from the ideal sech pulse spectrum causes a weak but significant pedestal in the time domain, the length of which may substantially exceed the pulse duration defined as the full width at half maximum (FWHM) intensity. This degradation in pulse quality may be unacceptable in a number of spectroscopic applications requiring high temporal resolution. An additional problem in the time domain is the increased sensitivity of the pulse width to the cavity and prism alignment. Cavity mirror alignment changes the position of the resonator axis and thus the glass path through the prisms. Hence any small cavity realignment calls for subsequent readjustment of the prism positions and orientation to restore the original pulse width and the corresponding spectrum. This makes “turn-key” operation and thus the integration of these devices in complex systems [e.g. chirped pulse amplification (CPA) systems, opto-electronic data processing systems] extremely difficult. Furthermore, the minimum prism separation sets a constraint on the resonator length and, in turn, the size and repetition rate of femtosecond-pulse solid-state laser oscillators. Continuous wave, ps, and fs lasers contain optical coatings as important functional elements, e.g., high reflectors (HR), output couplers (OC), and antireflection (AR) coatings. These optical elements are based on the interference phenomenon of light. Their theoretical analysis generally relies on the well-known scattering matrix formalism [12, 13] derived from the Maxwell equations. Laser performance strongly depends on the quality of optical coatings: the high reflec-

Time-resolved thermoreflectivity of thin gold films and its dependence on film thickness

Abstract: to \valunit{500}{nm} have been measured by femtosecond time-resolved pump-probe experiments. A conspicuous change of the relaxation behavior was found around \valunit{100}{nm} for pump pulse fluences of \valunit{1}{mJ/cm^{2}} . Thicker films show a nearly exponential decay of the transient linear reflectivity, which turns into a linear decay during the first \rangeunit{5}{7}{ps} for films with thicknesses of \valunit{100}{nm} or less. This observation is evidence of a mean free path of about \valunit{100}{nm} for hot electrons with temperatures around \valunit{1500}{K} .

Semiconductor saturable-absorber mirrors supporting sub-10-fs pulses

Abstract: We generated self-starting sub-10-fs pulses from a Ti:sapphire laser using a combination of a broadband semi- conductor saturable absorber mirror (SESAM), novel double- chirped mirrors, and Kerr-lens modelocking. We present a de- tailed overview of broadband SESAMs used in Ti:sapphire lasers and discuss their design issues. Using such a SESAM to assist the KLM process, we have generated pulses with a duration of only 6: 5f s, the shortest to date directly from the laser. Pulses as short as 13 fs were generated by soliton modelocking alone. Higher-order dispersion compensation was achieved with novel double-chirped mirrors in combina- tion with intracavity prisms.

The ultrahigh-peak-power laser: present and future

Abstract: to 1020-W/cm2 range. With some refinements and with superior energy storage materials, even higher peak power in the petawatt range should be possible from tabletop systems. In this paper we show the ultimate achievable power and intensity, as well as their applications in science and technology. Their applications cover a wide variety of fields, such as precision surgery, micromachining, coherent and incoherent X-ray generation, thermonuclear ignition, particle acceleration, and nonlinear quantum electrodynamics.

Efficient laser performance of Nd:YAG at 946 nm and intracavity frequency doubling with LiJO3, β-BaB2O4, and LiB3O5

Abstract: , β-BaB2O4, and LiB3O5 yielded a maximum output power of 550 mW at 473 nm with β-BaB2O4 as the nonlinear crystal.

Large third-order nonlinear optical susceptibility of Au-Al2O3 composite films near the resonant frequency

Abstract: O3 composite films with high Au concentrations (30%–60% in volume fraction) were prepared by reactive co-sputtering and post rapidly thermal annealing. The structure of the films and the size distributions of the Au nanoclusters were examined by TEM, and the third-order nonlinear optical susceptibility χ(3) was measured by degenerated four-wave mixing using a 70-ps pulse laser at 532 nm. The maximum value of the χ(3) was about 1.2×10-6 esu in the annealed films and occurred at around 45% Au concentration. The figure of merit, χ(3)/α (α is the absorption coefficient), has a value of 7×10-12 esu cm over a wide range of Au concentrations.

Diode-pumped thin-disk Yb:YAG regenerative amplifier

Abstract: . A passively modelocked 750-fs Yb:YAG oscilla-tor is used as the seed laser for a diode-pumped thin diskYb:YAG regenerative amplifier. Pulse energies of 180mJ areobtained at repetition rates of up to 750Hz,and120mJ pulseswere achieved at 1kHz. The amplified pulse duration was2 : 3ps, resulting in a pulse peak power of 78MW.Thein-crease in pulse duration during amplification is attributed togain narrowing in the amplifier material rather than to intra-cavity dispersion.PACS: 42.60; 42.55; 42.65Compact sources of ultrashort laser pulses at microjoule tomillijoule energy levels are of interest for several applica-tions, such as medical surgery, industrial machining, or non-linear frequency conversion. The development of powerfullaser diodes, matching the absorption wavelengths of manysolid state materials, made it possible to build compact andefficient modelocked oscillators and regenerative amplifiers.Typical pulse durations of diode-pumped passively mode-locked oscillators range from below 100fs to a few ps [1].However, most experiments on diode-pumped regenerativeamplifiers have been performed in the regime of 10 ps andmore. For example, pulse energies of 90mJ and 750 mJ wereextracted from cw diode-pumped Nd:YLF regenerative am-plifiers with 2Wand 15 W of pump power, respectively[2,3].Furthermore, 2

Measurements of picosecond laser induced fluorescence from gas phase 3-pentanone and acetone: Implications to combustion diagnostics

Abstract: between 323 K and 473 K at pressures of air or nitrogen between 0.1 MPa and 1.0 MPa.

Femtosecond decay-time measurement of electron-plasma oscillation in nanolithographically designed silver particles

Abstract: The decay time of the electron-plasma oscillation in silver nanoparticles is measured at a nanoparticle film consisting of regularly arranged, identically shaped and identically oriented particles. By design of a noncentrosymmetric particle shape, SHG in transmission at normal incidence of the fundamental beam is obtained. Therefore the autocorrelation function of the optical near field oscillation of the particle, excited by two emporally overlapping fs laser pulses separated by a defined delay time, could be measured. A decay time of 101 fs was extracted. This result shows that the damping of the electron-plasma oscillation in nanometric particles is approximately a factor of 2 larger than expected from the value of the imaginary part of the bulk metal dielectric funtion when consideration of the radiation damping in the particles is included.

Hexagonal nanostructures generated by light masks for neutral atoms

Abstract: Cr, different patterns can be generated. Possible applications using the inherent properties of atom lithography, e.g. the fabrication of photonic bandgap material, are discussed.

Quantum nondemolition measurement by optomechanical coupling

Abstract: We show that a single-port optical cavity with a movable mirror can provide a quantum non-demolition measurement of the intensity of a light beam. Due to radiation pressure, the cavity length is sensitive to the light intensity and can be measured with a secondary light beam. Signal-meter correlations can be made very large even at non-zero temperature. We study these correlations when the moving mirror is a plane–convex crystal resonator and we show the importance of spatial matching between light and acoustic modes.

2-d absolute oh concentration profiles in atmospheric flames using planar lif in a bi-directional laser beam configuration

Abstract: A technique has been developed to measure the absolute OH concentration at atmospheric pressures by using a combination of direct absorption and laser-induced fluorescence (LIF) detection. The technique is independent of collisions, because it uses laser beams in a bi-directional configuration, thereby eliminating collisional quenching. The absolute OH concentration is measured spatially resolved in two dimensions by using absorption on the Q(1)(6) rotational line in the A(2) Sigma(+) (upsilon' = 0) <-- X-2 Pi(upsilon '' = 0) band of OH at 309 nm. The requirements for obtaining a good signal-to-noise ratio for the technique are discussed and the possibilities of single-shot measurements are investigated.

Infrared cavity ringdown laser absorption spectroscopy (ir-crlas) in low pressure flames

Abstract: fractional absorption) and generality of IR-CRLAS for combustion studies is demonstrated for low pressure laminar flames and is shown to be robust even in sooting environments with high temperature gradients. The ability to obtain (1-D) spatially resolved spectra of both reactants and products within a narrow spectral region is also demonstrated. In these initial flame studies, two information rich mid-infrared spectral regions are probed at Doppler-limited resolution, centered about 1.5 μm and 3.3 μm.

Simultaneous detection of CO and CO2 using a semiconductor DFB diode laser at 1.578 μm

Abstract: and CO at a wavelength of λ=1578 nm. Sensitivity measurements under different conditions have been performed and the detection limit of the apparatus was measured to be less than 10 mTorr over a 1-m path length. In addition, we measured for the first time environmentally and spectroscopically relevant self-broadening and nitrogen-broadening coefficients for CO2 and CO in this spectral region and we discuss different possibilities for increasing the sensitivity of the apparatus.

Picosecond Z-scan study of bound electronic Kerr effect in LiNbO3 crystal associated with two-photon absorption

Abstract: crystal have been measured using Z-scan technique with picosecond pulses at 532 nm. The nonlinear absorption coefficient and nonlinear refractive index are determined to be 2.5×10-10 cm/W and 5.3×10-15 cm2/W, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the reported Z-scan results in LiNbO3 obtained with cw laser beam at 514 nm. The nonlinearities in LiNbO3 induced by 532 nm picosecond pulses are believed to be mainly due to two-photon absorption and bound electronic Kerr effect associated with the two-photon absorption.

Laser-induced fluorescence study of a xenon Hall thruster

Abstract: 0→6p[3/2]2(3P2-1D2) transition at 823.2 nm and the xenon-ion 5d[3]7/2→6p[2]5/2 0(4D7/2-4P5/2) transition is used to measure plasma parameters in the plume of a laboratory-model xenon Hall thruster. The Hall discharge operates nominally at 62 V, 4.2 A, and 3.2 mg s-1 xenon flow, with an overall thruster power of 320 W. A tunable semiconductor diode laser and an Ar+-pumped dye laser are used to probe the respective excited-state transitions. Axial velocity measurements are made at a number of axial and radial locations up to 4.5 cm downstream of the thruster-exit plane and under a variety of thruster operating conditions. Neutral velocities from 100 m s-1 to 400 m s-1 and ion velocities as high as 12 km s-1 are calculated from measured Doppler shifts. The charge-exchange phenomenon evidently does not significantly affect the xenon neutrals. The spectral-line shapes of the ion indicate a spread in ion energies through a non-Maxwellian distribution of axial velocities. Neutral kinetic temperatures of 500 (±200) K are observed under standard operating conditions. Zeeman and Stark effects on the spectral-line shapes, from the thruster’s magnetic and electric fields, are not substantial. The measured line center of the ion transition is 16521.23 (±0.02) cm-1.

High-power sub-10-fs Ti: sapphire oscillators

Abstract: The state of the art of mirror-dispersion-controlled (MDC) Ti:sapphire laser oscillators is reviewed. Owing to improvements in the cavity and mirror design, these systems can now routinely generate sub-10-fs pulses with peak powers exceeding the megawatt level. The unique compactness of MDC Ti:sapphire oscillators results in excellent noise characteristics, a nearly diffraction limited output, and a high reproducibility of performance. Employing a diode-pumped solid-state laser as a pump source allows the generation of sub-10-fs pulses from an all-solid-state laser for the first time. PACS: 42.55.Rz; 42.60.Mi; 42.65.Re Titanium-doped sapphire lasers [1] generating ultrashort pulses by Kerr-lens mode locking (KLM) [2–7] are now widely used for time-resolved studies in physics, chemistry, biology, and electronics, as well as for seeding high-power solid-state amplifier systems. After its first demonstration by Spence and co-workers in 1990 [2], the performance of KLM Ti:sapphire oscillators had been subject to a rapid progress [8], which temporarily culminated in the development of fused-silica-prism-controlled systems [9]. When detuned to ≈ 850 nm, these systems have been capable of generating pulses of around 10 fs or slightly shorter in duration [10, 11], which were limited by the fourth-order dispersion introduced by the prisms [12]. This performance came at the expense of a large (> 0.6) time–bandwidth product and a significant red shift of the spectrum from the gain peak of Ti:sapphire, impairing the suitability of this broadband output for seeding Ti:S amplifiers. With the advent of dispersion-engineered chirped multilayer dielectric mirrors [13] a new generation of mirrordispersion-controlled (MDC) Ti:sapphire lasers has been developed [14–17] which were able to overcome the limitations inherent in prism-controlled oscillators. In MDC oscillators the mirrors not only provide feedback but also introduce broadband negative dispersion indispensable for soliton-like pulse formation [18]. Hence they obviate the need for intracavity prisms, allowing the construction of femtosecond Ti:S oscillators containing no intracavity components other than the gain medium (and an optional aperture). This unprecedented simplicity and compactness come in combination with a reliable sub-10-fs performance in the 800-nm wavelength range. Owing to these unique features, sub-10-fs MDC Ti:sapphire oscillators are likely to become an important workhorse for a number of application fields, particularly where high time resolution, high peak power, solid-state ruggedness, and reliability are important. In this paper, we shall report on recent progress in MDC Ti:S oscillator technology, which has permitted the generation of femtosecond pulses with peak powers exceeding 1 MW for the first time directly from a laser oscillator. As this output is delivered in a nearly diffraction-limited beam, these sub-10-fs pulses are expected to be focusable to intensities well beyond the terawatt/cm2 level. This performance is unprecedented in a cw mode-locked laser. Yet higher peak powers can be achieved by cavity dumping [19, 20] or external amplification [21] at reduced repetition rates. The advanced sub-10-fs oscillator technology is the result of recent innovations in the design and optimization of KLM oscillators as well as of progress in chirped mirrors technology [22]. In what follows we shall focus on the laser design; details about the chirped mirror characteristics will be published elsewhere. After considering some general guidelines for optimizing KLM oscillators for maximum output pulse energy, the results of the optimization of MDC oscillators Kerr-lens mode-locked by using hard and soft apertures will be presented. The pulses delivered by the oscillators have been characterized temporally, spectrally, spatially (beam profile, M2), as well as in terms of their energy noise and timing jitter. Finally, the major characteristics of an allsolid-state sub-10-fs laser will be briefly summarized. 1 Design considerations for high-power KLM oscillators In femtosecond solid-state lasers a soliton-like interplay between self-phase modulation (SPM) and negative group delay dispersion (GDD) dominates the formation of an ultrashort pulse in the laser cavity. The separated action of SPM and GDD introduces a periodic perturbation to the soliton-like

Nanoscale atomic lithography with a cesium atomic beam

Abstract: line (852 nm) and a width of about 120 nm and covering a large area of approximately 1 mm2.

Precise measurement of methane in air using diode-pumped 3.4-μm difference-frequency generation in PPLN

Abstract: volume multi-pass absorption cell with an 18-m path length. The methane mixing ratio was determined by comparing the direct optical absorption measured in the sample with that measured in a reference gas at 100 torr and room temperature. Relative accuracy of better than 1 ppb (parts in 109, by mole fraction) was achieved in measurements of natural air that contained 1700–1900 ppb methane. The typical measurement time for each sample was 60 seconds. The accuracy was limited by residual interference fringes in the multi-pass cell that resulted from scattering. Without the use of reference samples, the relative accuracy was 20 ppb; it was limited by the long-term reproducibility of the spectroscopic baseline, which was affected by drift in the optical alignment coupled to changes in the ambient temperature. This work demonstrates the use of diode-pumped difference-frequency generation (DFG) in PPLN in a high-precision infrared spectrometer. Compact, room-temperature solid-state gas sensors can be built based on this technology, for accurate real-time measurements of trace gases in the 3–5 μm spectroscopic region.