Μm Laser Pulses Research Articles

Build-Up of a Resin Composite Core in a Fiber-Reinforced Post by a 2.78 µm-Pulsed Laser Treatment

Build-Up of a Resin Composite Core in a Fiber-Reinforced Post by a 2.78 µm-Pulsed Laser Treatment

Attosecond lighthouse driven by sub-two-cycle, 1.8 μm laser pulses

We generate space-time coupled attosecond pulse trains with a 1.8 μm wavelength laser pulse using the ‘attosecond lighthouse’ technique. We show low divergence, spatially well-separated beamlets from low ionization potential gas media. We also find that there is little long trajectory contribution—only the short trajectory contribution is clearly visible for any beamlet. These results open a new route for extending attosecond technology to higher cut off energy and shorter pulse duration.

Remote laser ablation electrospray ionization mass spectrometry for non-proximate analysis of biological tissues.

We introduce remote laser ablation electrospray ionization (LAESI), a novel, non-proximate ambient sampling technique. Remote LAESI allows additional analytical instrumentation to be incorporated during sample analysis. This work demonstrates the utility of remote LAESI and, when combined with optical microscopy, allows for the microscopy-guided sampling of biological tissues. Rapid prototyping using a 3D printer was applied to produce various ablation chamber geometries. A focused 5 ns, 2.94 µm laser pulse kept at 10 Hz ablated the sample within the chamber, remote to the mass spectrometer inlet. Ablated particulates were carried through a transfer tube by N2 gas, delivered to the electrospray plume and ionized. A long-distance microscope was used to capture images of tissues before, during and after ablation. Optimized remote LAESI was found to have a 27% transport efficiency compared with conventional LAESI, sufficient for many applications. A comparable molecular coverage was obtained with remote LAESI for the analysis of plant tissue. Proof-of-principle experiments using a pansy flower and a maple leaf indicated the functionality of this approach for selecting domains of interest for analysis by optical microscopy and obtaining chemical information from those selected regions by remote LAESI-MS. Remote LAESI is an ambient non-proximate sampling technique, proven to detect metabolites in biological tissues. When combined with optical microscopy, remote LAESI allows for the simultaneous acquisition of morphological and chemical information. This technique has important implications for histology, where chemical information for specific locations within a tissue is critical.

Self-compression of terawatt level picosecond 10 μm laser pulses in NaCl

We propose and numerically validate a self-compression regime of powerful 10 μm laser radiation (power 500 GW, energy 1.5 J, pulse duration 2.5 ps) in a NaCl crystal, taking into account its nonlinear and dispersive properties. We demonstrate numerically that the proposed scheme—a solid state compressor containing four NaCl plates (total thickness 19 cm) and divided by spatial filters—avoids the small-scale self-focusing process and reduces by an order of magnitude the initial pulse duration, from 2.5 ps up to 250 fs (seven periods of oscillation) and increases output power from 0.5 TW up to 2.2 TW.

Diode-pumped Er3+:Yb3+:NaCe0.43Gd0.57(WO4)2 pulse laser passively Q -switched with a Co2+:Mg0.4Al2.4O4 saturable absorber at 1.53 μ m

Based on the long fluorescence lifetime of upper laser level 4I13/2 of Er3+ ions and high 1.5−1.6 μm laser operation efficiency, an Er3+:Y b3+:NaCe0.43Gd0.57(WO4)2 crystal was used to generate a Q-switched pulse laser with high energy and low threshold. End-pumped by a 970 nm diode laser, a passively Q-switched 1.5−1.6 μm pulse laser was first realized in an Er3+ and Y b3+ co-doped tungstate crystal, when a Co2+:Mg0.4Al2.4O4 spinel crystal was used as saturable absorber. A 1.53 μm pulse laser with about 22 μJ energy, 76 ns duration and 21 kHz repetition rate was obtained at an absorbed pump power of 12 W in a c-cut 1.7-mm-thick Er3+:Y b3+:NaCe0.43Gd0.57(WO4)2 crystal.

Saturation and Polarization Characteristics of 1.56 μm Optical Probe Pulses in a LTG-GaAs Photoconductive Antenna Terahertz Detector

The characteristics of low temperature-grown GaAs photoconductive antenna (PCA) terahertz detectors probed by 1.56 μm laser pulses are investigated. The influence of TM and TE polarized probe, as well as the saturation characteristics are studied for 2 μm- and 5 μm-gap PCA’s. Different polarization characteristics at low probe powers and at the saturation regimes were observed. Results are explained in terms of the polarization-dependent photocarrier distribution at the PCA gap arising from tight focusing. This work also demonstrates using a 1.56 μm probe for a GaAs PCA to achieve ~60 dB SNR; matching its performance characteristics for above-bandgap probes.

Hybrid-pumped, gain-switching operation of a Tm-doped fiber laser with linear-polarized output

We report an all-fiber laser with a linear-polarized, pulsed 2 μm output up to 4.6 W by applying a hybrid-pump gain-switched scheme. In this method, a 790 nm laser diode serves as the main supplier of inverse population while a 1 μm pulsed Yb-doped fiber laser triggers the 2 μm pulsed lasing, to realize the gain-switching operation. We construct a resonant cavity with a polarization-maintaining Tm-doped fiber and a fiber Bragg grating to achieve a polarized laser. The laser output is centered at 2021 nm and has a polarization extinction ratio of 13.7 dB; the maximum pulse energy is 230 μJ at a repetition rate of 20 kHz.

Thulium Laser Supported Nephron Sparing Surgery for Renal Cell Carcinoma

We analyze the feasibility, advantages and results of the use of a thulium laser in nephron sparing surgery for renal cell carcinoma. In this single center prospective study 10 consecutive high risk patients underwent open or laparoscopic thulium laser assisted enucleation for small peripheral renal cell carcinoma at our department. We used a 2.0 μm continuous or pulsed thulium laser. This diode pumped solid state laser emits a wavelength of 2,013 nm in the infrared spectrum and penetrates tissue to a depth of 0.5 mm. The entire tumor enucleation was performed using the frontal thulium laser fiber. In all cases the thulium laser produced a smooth incision of the renal parenchyma and a safe delineation of the plane between the tumor and the surrounding tissue. In addition, in the off clamp procedures bleeding was limited during the dissection and did not interfere with the definition of the surgical plane. Median surgical time from the beginning of the laser assisted tumor dissection to the end, after verification of bleeding control on the cut surface, was 15 minutes (range 12 to 20). No significant (less than 40 cc) blood loss occurred during the laser assisted tumor dissection. All cases were clear cell renal cell carcinoma and no positive surgical margins were found. In all cases postoperative management was uncomplicated without evidence of hemorrhage. In our prospective preliminary experience, thulium laser assisted enucleation for renal cell carcinoma is a feasible, safe and effective procedure.

Narrow-pulse-width gain-switched thulium fiber laser

A hybrid-pumped gain-switched Tm3+ fiber laser with an all-fiber configuration is demonstrated to achieve over 10 W 2 μm pulsed laser beams. This laser system is complementarily pumped by a 790 nm continuous-wave diode laser and a 1 μm pulsed Yb3+ fiber laser. Based on the triggering effect of a 1 μm pulse pump and the Rayleigh scattering induced Brillouin scattering effect, the 2 μm laser pulse can be narrowed to less than 20 ns, which is the narrowest pulse width ever achieved in high-power gain-switched thulium fiber lasers. The maximum pulse energy is 2 mJ and the maximum peak power is over 100 kW. Supercontinuum generation spanning over 200 nm can be observed with an average-power spectral density of >30 mW nm−1.

Interaction of 0.53 μm laser pulse with millimeter-scale plasmas generated with gas-bag target

Reported are the interactions of 0.53 μm laser pulse with millimeter-scale plasmas that are produced with gas-bag target irradiated with 0.35 μm laser pulses. The generated plasmas are characterized with collective Thomson scattering and space- and time-resolved X-ray images. The density of the plasmas is about 0.1 n c corresponding to the 0.53 μm laser beam, and the temperature is about 0.64 keV with a filling gas of C5 H12 . The interaction laser beam can output 1.0 kJ energy within the duration of 1 ns at the wavelength of 0.53 μm, leading to a nominal intensity less than 1.5 × 1015 W/cm2 . The reflectivity of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is measured with a full aperture backscatter system. The experimental results show than the reflectivity of SBS is less than 5% and that of SRS is less than 1%. It is a positive result with respect to using 0.53 μm lasers as drivers for laser fusion.

Carrier envelope phase effects in strong field ionization of xenon with few-cycle 1.8 μm laser pulses

Interferometrically CEP controlled few-cycle IR pulses revealed a strong influence on both, directly ionized and rescattered electrons in xenon for pulse durations from 2 to 5 cycles.

1.5 to 1.6μm pulsed laser diode bars based on epitaxially stacked AlGaInAs/InP heterostructures

This paper describes pulsed laser diode bars based on epitaxially stacked double AlGaInAs/InP heterostructures. The output power of such bars is 1.8 times that of single-heterostructure laser diode bars. We present the key characteristics of the laser sources.

Kinetics of Coil-to-Globule Transition of Dansyl-Labeled Poly(N-sopropylacrylamide) Chains in Aqueous Solution

The coil-to-globule transition of thermally sensitive linear poly(N-isopropylacrylamide) (PNIPAM) labeled with dansyl group is induced by 1.54 μm laser pulses (width≈10 ns). The dansyl group is used to follow the transition kinetics because its fluorescence intensity is very sensitive to its micro-environment. As the molar ratio of NIPAM monomer to dansyl group increases from 110 to 300, the effect of covalently attached dansyl fluorophores on the transition decreases. In agreement with our previous study in which we used 8-anilino-1-naphthalensulfonic acid ammonium salt free in water as a fluorescent probe, the current study reveals that the transition has two distinct stages with two characteristic times, namely, τfast≈0.1 ms, which can be attributed to the nucleation and formation of some “pearls" (locally contracting segments) on the chain, and τslow≈0.5 ms, which is related to the merging and coarsening of the “pearls". τfast is independent of the PNIPAM chain length over a wide range (Mw=2.8×106–4.2×107 g/mol). On the other hand, τslow only slightly increases with the chain length.

Diode-Pumped Actively Q-Switched Nd:Lu0.1Y0.9VO4Laser at 1.34 µm

The continuous-wave (CW) and acoustooptic (AO) Q-switched 1.34 µm laser performance of Nd:Lu0.1Y0.9VO4 crystals was demonstrated. In all operations, an a-cut crystal behaved better than a c-cut crystal. With a T = 3.9% output coupler, the maximum CW output power was 2 W, which corresponded to an optical conversion efficiency of 30.8%. At a pulse repetition frequency (PRF) of 5 kHz, the shortest pulse width, largest pulse energy, and highest peak power were 23.8 ns, 124 µJ, and 5.21 kW, respectively. As we have known, these are the best results obtained for a 1.34 µm pulsed laser based on mixed vanadate crystals.

Diode-Pumped Actively Q-Switched Nd:Lu0.1Y0.9VO4 Laser at 1.34 µm

The continuous-wave (CW) and acoustooptic (AO) Q-switched 1.34 µm laser performance of Nd:Lu0.1Y0.9VO4 crystals was demonstrated. In all operations, an a-cut crystal behaved better than a c-cut crystal. With a T = 3.9% output coupler, the maximum CW output power was 2 W, which corresponded to an optical conversion efficiency of 30.8%. At a pulse repetition frequency (PRF) of 5 kHz, the shortest pulse width, largest pulse energy, and highest peak power were 23.8 ns, 124 µJ, and 5.21 kW, respectively. As we have known, these are the best results obtained for a 1.34 µm pulsed laser based on mixed vanadate crystals.

Interaction of 0.53 μm laser pulse with millimeter-scale plasmas generated by gasbag target

Detailed research on the interaction of a 0.53 μm laser pulse with millimeter-scale plasmas produced by a gasbag target on the Shengguang-II facility is presented. The x-ray pinhole images confirm that millimeter-scale plasmas are generated and the x-ray framing images show a temporal window of 0.6–1.1 ns during which the millimeter-scale plasmas exist. The electron temperature is measured with a collective Thomson scattering system, providing 0.64 keV for C5H12 and 1.8 keV for Xe plasmas. The electron density is inferred from the stimulated Raman scattering spectra. The experimental spectra show large differences for C5H12- and Xe-filled gasbags. A one-dimensional code based upon steady-state, kinetic linear theory is applied to calculate the stimulated Raman scattering spectra. Excellent agreement between the calculated and experimental results shows that the plasma parameters, especially the electron density and the temperature, dominate the disruption behavior of stimulated Raman scattering. The results also indicate that stimulated Raman scattering is probably located within specific region of the gasbag. The time-integrated reflectivity of both the stimulated Raman and Brillouin scattering is at a low level, even in the conditions of high laser intensity (1.5×1015 W/cm2) and no beam-smoothing. The experimental results are promising for future ignition experiments with a 0.53 μm laser as the driver.

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.

Tunable wide-angle acousto-optic filter in single-crystal tellurium

The acoustic, optic and acousto-optic properties of tellurium crystals have been examined in order to develop an acousto-optic tunable filter (AOTF) operating in the long-wave infrared (LWIR) region. The AOTF design is based on the wide-angle regime of light diffraction in the YZ plane of the birefringent crystal operating from 8.4 to 13.6 µm. Device characteristics were obtained from both theoretical and experimental investigations. Experiments were carried out using both a 10.6 µm pulsed CO2 laser as well as a tunable CO2 laser operating in a continuous wave mode from 9.2 to 10.7 µm. The AOTF was tuned over the acoustic frequency range of 81.5–94.7 MHz. The filtering performance in the tellurium device was provided by a pure shear elastic wave propagating at a 95.8° angle with respect to the positive direction of the optic axis, while an ordinary polarized optical beam was incident at the Bragg angle of 6.0° relative to the acoustic wavefront. At 10.6 µm, the measured spectral bandwidth of the filter was 127 nm and the optical transmission coefficient was around 8.8% with 2.0 W drive power. This paper presents detailed results from both the theoretical as well as experimental device characterization including the spectral images obtained with a 256 × 256 mercury cadmium telluride camera cooled to 77 K.

High-power mid-infrared tunable optical parametric oscillator based on 3-mm-thick PPMgCLN

The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at 10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91 μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was about ±4% in 10 min continuous operation. The beam quality factor M 2 was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C.

Mid-infrared laser-driven broadband water-window supercontinuum generation from pre-excited medium

We theoretically investigate the broadband water-window supercontinuum generation from pre-excited medium with a mid-infrared pulse. We find that the wavelength scaling of the harmonic yield from near-visible (0.8 μm) to mid-infrared (1.8 μm) in single-atom level is λ(-2.7). Using an intense phase-stabilized few-cycle 1.6 μm laser pulse, a broadband water window supercontinuum with bandwidth of approximately 140 eV is obtained. We also investigate the macroscopic effects and find that large initial population of the excited state leads to the high-density of free electrons, which shift the carrier-envelop phase of the driving pulse and further diminish the water-window supercontinuum generation. The highly-ionized medium also results in poor temporal and spatial properties of the attosecond pulse. Instead, small initial population of the excited state can produce well phase-matched xuv supercontinuum in water-window region and an 100-as pulse with central wavelength of 2.8 nm and pulse energy of 0.15 nJ can be filtered out.