High-power, Yb-fiber-laser-pumped, picosecond parametric source tunable across 752-860 nm

We report a stable, high-power source of picosecond pulses in the near-infrared based on intracavity second harmonic generation (SHG) of a MgO:PPLN optical parametric oscillator synchronously pumped at 81 MHz by a mode-locked Yb-fiber laser. By exploiting the large spectral acceptance bandwidth for Type I (oo→e) SHG in β-BaB2O4 and a 5 mm crystal, we have generated picosecond pulses over 752-860 nm spectral range under minimal angle tuning, with as much as 3.5 W of output power at 778 nm and >2 W over 73% of the tuning range, in good beam quality with TEM00 spatial profile and M2<1.4. The SHG output pulses have durations of 15.2 ps, with a spectral bandwidth of ～3.4 nm at 784 nm. In addition, the oscillator simultaneously provides a signal power of >1 W over 1505-1721 nm (25 THz) and idler power >1.8 W over 2787-3630 nm (25 THz), corresponding to a total (signal plus idler) tuning range of 1059 nm. The SHG, signal, and idler output exhibit passive long-term power stability better than 1.6%, 1.3%, and 1.6% rms, respectively, over 14 h.     

High-power 200 fs Kerr-lens mode-locked Yb:YAG thin-disk oscillator

We demonstrate a power-scalable Kerr-lens mode-locked Yb:YAG thin-disk oscillator. It delivers 200 fs pulses at an average power of 17 W and a repetition rate of 40 MHz. At an increased (180 W) pump power level, the laser produces 270 fs 1.1 μJ pulses at an average power of 45 W (optical-to-optical efficiency of 25%). Semiconductor-saturable-absorber-mirror-assisted Kerr-lens mode locking (KLM) and pure KLM with a hard aperture show similar performance. To our knowledge, these are the shortest pulses achieved from a mode-locked Yb:YAG disk oscillator and this is the first demonstration of a Kerr-lens mode-locked thin-disk laser.     

Regenerative amplification of femtosecond laser pulses in Ti:sapphire at multikilohertz repetition rates

We have generated and applied noncoherent x-ray radiation in an all-solid-state laser system operating at repetition rates up to 20 kHz. Based on a model that takes into account the strong thermal loading of the Ti:sapphire rod, a laser cavity with low sensitivity to thermal lensing was chosen. With a maximum pump power of 80 W, an output power as high as 27 W was obtained in gain-switched operation, and, with a seeding from a femtosecond oscillator, 60-fs, 0.8-mJ (8-W) pulses at 10 kHz and 0.32-mJ (6.5-W) pulses at 20 kHz were generated. High power femtosecond output was used to generate x-ray continuum radiation up to 5 keV from a liquid-gallium jet target.     

Two-color pulse compression in aperiodically-poled lithium niobate

We experimentally demonstrate engineerable compression of two-colored pulses in a linearly-chirped quasi-phase-matching grating. Quadratic solitons generated from fundamental input are reshaped through cascaded parametric processes of second-harmonic generation (SHG) and the back-conversion. We use type-I (e: o + o) SHG geometry in a 50-mm-long aperiodically-poled MgO:LiNbO₃ device to satisfy the group-velocity matching condition. Simultaneously compressed fundamental and SH pulses of about 55-fs duration with small pedestal are generated from the fundamental input pulses of 95-fs duration.     

Frequency doubling of phase-modulated femtosecond laser pulses in periodically poled and chirped nonlinear crystals

The second harmonic generation (SHG) at a wavelength of 0.8 μm by 50-and 10-fs pulses with and without phase modulation (PM) was systematically studied in LiNbO₃ crystals with regular domain structure and linearly varied domain thickness. The main results were obtained by numerical method, taking into account the difference between group velocities of interacting pulses and the group-velocity dispersion. In the approximation of the given field of the fundamental radiation, an analytical expression was derived for the spectral density of the second harmonic in the periodically poled nonlinear crystal (PPNC) under nonstationary excitation conditions. It was numerically found that the conversion efficiency of about 90% can be achieved by doubling the frequency of 50-fs laser pulses without PM in the LiNbO₃ PPNC. The maximum conversion efficiency for the SHG by PM pulses is achieved at a certain optimum chirp step in the crystal domain length, which depends on both the value and sign of frequency modulation.     

Characterization of sub-10-fs pulse focusing with high-numerical-aperture microscope objectives

Dispersion precompensation with a prism sequence and a third-order dispersion mirror resulted in negligible broadening of sub-10-fs pulses at subwavelength spot sizes when the pulses were focused with microscope objectives and moderate apertures. At larger apertures, lens chromaticity and spherical aberration led to an effective pulse broadening of up to 1.3x , depending on the aperture size and the detector position. The data suggest that intensities exceeding 10(14) W/cm(2) can be produced directly from femtosecond pulse oscillators.     

Femtosecond diode-pumped Nd:glass laser with more than 1 W of average output power

We have demonstrated 175-fs pulses with 1 W and 300-fs pulses with 1.2 W of average output power at a pulse repetition rate of 117 MHz from a Nd:phosphate (Schott LG 760) glass laser pumped by a 1-cm-wide, 20-W diode laser bar. Stable soliton mode locking was achieved by use of an intracavity semiconductor saturable absorber mirror. We obtained more than 2 W of average power without mode locking. Using cylindrical cavity mirrors, we adapted the laser mode inside the Nd:glass to the highly elliptical pump beam in both dimensions (tangential and sagittal axes) while maintaining a nearly ideal circular TEM(00) output beam with M(2) approximately 1.2 . Overpumping the laser mode in the tangential plane and efficient unidirectional heat removal in the sagittal plane using a 0.8-mm thin Nd:glass also contributed to the good output-beam quality.     

All-solid-state generation of 100-kHz tunable mid-infrared 50-fs pulses in type I and type II AgGaS(2)

We report the operation of an all-solid-state system for the generation of tunable mid-infrared sub-50-fs pulses. A Ti:sapphire regenerative amplifier, pumped by 10 W of power from 532-nm, diode-pumped, frequency-doubled Nd:YVO(4) lasers, produced 4-muJ energy, sub-50-fs pulses at 800 nm with a 100-kHz repetition rate. This output was used to drive a beta-BaB(2)O(4) optical parametric amplifier followed by a difference-frequency generator based on a AgGaS(2) crystal. Continuous tuning of ultrafast pulses from 2.4m to longer than 12mum was obtained. A performance comparison of difference-frequency generation in type I and type II phase-matched AgGaS(2) is reported.     

High-average-power kilohertz-repetition-rate sub-100-fs Ti:sapphire amplifier system

We report on a femtosecond Ti:sapphire laser amplifier system that generates pulse energies >5 mJ at a 1-kHz repetition rate. The system consists of regenerative and multipass amplifiers and uses the technique of chirped-pulse amplification. When the system was seeded with 70-fs pulses at 800 nm from a self-mode-locked Ti:sapphire oscillator, amplified pulses of 94-fs duration at a repetition rate of 1 kHz and an average output power of 5.4 W were produced. The amplified pulse-repetition rate is variable from 250 Hz to 3 kHz. Pulse energies of >7.5 mJ were obtained at 500 and 250 Hz.     

Continuous-wave mode-locked Ti:sapphire laser focusable to 5 x 10(13) W/cm(2)

Generation of sub-10-fs pulses with an average power of 1 W and a peak of 1.5 MW from a Kerr-lens mode-locked mirror-dispersion-controlled Ti:sapphire laser is demonstrated. A specially designed lens triplet focuses the output of this compact all-solid-state source to a peak intensity in excess of 5x10(13) W/cm (2) . Nonperturbative nonlinear optics is now becoming feasible by use of the output of a cw mode-locked laser.     

Nonlinear femtosecond pulse compression at high average power levels by use of a large-mode-area holey fiber

We demonstrate that nonlinear fiber compression is possible at unprecedented average power levels by use of a large-mode-area holey (microstructured) fiber and a passively mode-locked thin disk Yb:YAG laser operating at 1030 nm. We broaden the optical spectrum of the 810-fs pump pulses by nonlinear propagation in the fiber and remove the resultant chirp with a dispersive prism pair to achieve 18 W of average power in 33-fs pulses with a peak power of 12 MW and a repetition rate of 34 MHz. The output beam is nearly diffraction limited and is linearly polarized.     

Second-harmonic generation in a near-field optical-fiber probe

Second-harmonic generation (SHG) in a near-field optical-fiber probe was observed. The tip of the probe consists of a triple-tapered fiber with an aluminum coating. For a fiber probe with an aperture size of 100 nm, the SHG conversion factor was 2.0 x 10(-11)cm(2)/W , which is as large as that of a 5-mm KDP crystal. In a probe-to-probe experiment, we demonstrated that SHG took place at the aluminum coating on the fiber probe.     

Diode-pumped femtosecond Yb:KGd(WO(4))(2) laser with 1.1-W average power

We demonstrate what is to our knowledge the first mode-locked Yb:KGd(WO(4))(2) laser. Using a semiconductor saturable-absorber mirror for passive mode locking, we obtain pulses of 176-fs duration with an average power of 1.1 W and a peak power of 64 kW at a center wavelength of 1037 nm. We achieve pulses as short as 112 fs at a lower output power. The laser is based on a standard delta cavity and pumped by two high-brightness laser diodes, making the whole system very simple and compact. Tuning the laser by means of a knife-edge results in mode-locked pulses within a wavelength range from 1032 to 1054 nm. In cw operation, we achieve output powers as high as 1.3 W.     

Femtosecond Ti:sapphire ring laser with a 2-GHz repetition rate and its application in time-resolved spectroscopy

A Kerr-lens mode-locked femtosecond Ti:sapphire laser operating at a repetition rate of 2 GHz is demonstrated. A mirror-dispersion-controlled unidirectional ring cavity delivers nearly bandwidth-limited pulses of 23-fs length. Mode locking is self-starting without a hard aperture in the cavity. The advantages of this high-repetition-rate oscillator in optical time-resolved spectroscopy are demonstrated.     

Electrooptical sampling of ultra-short THz pulses by fs-laser pulses at 1060 nm

Electrooptical sampling of ultra-broadband terahertz (THz) radiation with the help of ultra-short 1060-nm pulses is reported for the first time. The THz pulses are generated by exciting a surface emitter (InAs) with a parabolic fiber laser amplifier delivering 100-fs pulses at a repetition rate of 75 MHz and an average power of 10 W. ZnTe and GaP crystals are used for detection and their velocity mismatch is compared at 800 nm and 1060 nm. PACS 42.55.Wd; 42.70.Nq; 42.72.Ai     

16.2-W average power from a diode-pumped femtosecond Yb:YAG thin disk laser

We demonstrate a power-scalable concept for high-power all-solid-state femtosecond lasers, based on passive mode locking of Yb:YAG thin disk lasers with semiconductor saturable-absorber mirrors. We obtained 16.2 W of average output power in pulses with 730-fs duration, 0.47-muJ pulse energy, and 560-kW peak power. This is to our knowledge the highest average power reported for a laser oscillator in the subpicosecond regime. Single-pass frequency doubling through a 5-mm-long lithium triborate crystal (LBO) yields 8-W average output power of 515-nm radiation.     

Ultrawide tunable Er soliton fiber laser amplified in Yb-doped fiber

A Raman-shifted and frequency-doubled high-power Er-fiber soliton laser for seeding an efficient high-power Yb fiber femtosecond amplifier is demonstrated. The Raman-shifted and frequency-doubled Er-soliton laser is tunable from 1.00 to 1.070microm and produces bandwidth-limited 24-pJ pulses at a repetition rate of 50 MHz with a FWHM pulse width of 170 fs at 1.040microm . The Yb(3+) amplifier has a slope efficiency of 52% and generates 3-ps linearly chirped pulses with an average power of 0.8 W at 1.05microm . After pulse compression, 74-fs bandwidth-limited pulses with an average power of 0.4 W and a pulse energy of 8 nJ are generated.     

7.6-W diode-pumped femtosecond Yb:KGW laser

We have demonstrated a high power diode-pumped mode-locked femtosecond Yb:KGW laser with semiconductor saturable absorber mirror(SESAM). By using an output coupler with 10% transmittance, the laser delivered 160-fs pulses with average output power of 7.6 W at a repetition rate of 78 MHz, corresponding to pulse energy of 97 nJ and peak power of 606 kW.     

Sub-100 femtosecond pulses from a SESAM modelocked thin disk laser

We present the first passively modelocked thin disk laser (TDL) with sub-100-fs pulse duration using the broadband sesquioxide gain material Yb:LuScO₃ and an optimized SEmiconductor Saturable Absorber Mirror (SESAM). In this proof-of-principle experiment, we obtained 5.1 W of average power at a repetition rate of 77.5 MHz and a pulse duration of 96 fs. We carefully explored and optimized the different parameters on the soliton pulse formation process for the generation of short pulses. In particular, SESAMs combining fast recovery time, high modulation depth and low nonsaturable losses proved crucial to achieve this result even though they are expected to only play a minor role in soliton modelocking. To our knowledge, these are the shortest pulses ever obtained with a modelocked TDL, reaching for the first time the sub-100-fs milestone. This result opens the door to sub-100-fs oscillators with substantially higher power levels in the near future.     

Kerr-lens mode-locked polycrystalline Cr:ZnS femtosecond laser pumped by a monolithic Er:YAG laser

We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linearpolarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 m W. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.