Μm Laser Pulses Research Articles

2.09 µm high-gain, high-energy sub-nanosecond laser amplification system and its application to a millijoule-level mid-infrared ZnGeP2 optical parametric generator.

In this Letter, we report for the first time to our knowledge a 2 mJ-level 2.09 µm Ho:YAG regenerative amplifier (RA) seeded by the first-stage Ho-doped fiber (HDF) preamplifier of a gain-switched laser diode (GSLD). After the single-pass power amplifier (SPPA), the output of a 2.09 µm pulse laser with 1 kHz, 570 ps, and >10 mJ was achieved. The overall gain of the whole amplifier system was greater than 90 dB, providing a novel, stable, and reliable sub-nanosecond (sub-ns) pump source operating at a pulse repetition frequency (PRF) of 1 kHz for an optical parametric generator (OPG) based on ZnGeP2 (ZGP). Specifically, for the ZGP OPG structure, a maximum pulse energy of 1.82 mJ at 3-5 µm had been achieved with an injected pump pulse energy of 5.47 mJ, corresponding to a slope efficiency of 39.5% and an optical-to-optical conversion efficiency (OOCE) of 33.27%.

SHG behavior of the solid isomorphic compounds Ni- and Cu-5,10,15,20- tetraphenylporphyrinate. An experimental and theoretical study

We prepared and investigated the SHG behavior in the solid state of the two isomorphic Nickel and Copper 5,10,15,20-tetraphenylporphyrinate, that crystallize in the same acentric I4¯2d space group. The compounds were synthesized and characterized, and the Second Harmonic Generation (SHG) response of powdered samples was measured employing a 1.907 μm pulsed laser radiation. During laser irradiation, for both compounds, a gradual increase of the intensity of the SH signal was observed until, after a few minutes, it reached a plateau of about fifty times (for the Ni-TPP) or ten times (for the Cu-TPP) the initial value. We attempted to understand the origin of this phenomenon both through experimental analysis and theoretical calculations. Absorption and vibrational spectroscopies, in solution and solid state, combined with powder X-ray diffraction, both before and after irradiation, do not evidence any chemical degradation, phase transition or amorphization process. Theoretical calculations on little fragments of the Ni/Cu-TPP structure simulate appropriately the structural features of the complexes and their initial experimental SHG response. Magnetic balance measurement in the solid state before and after irradiation, in conjunction with DFT/B3LYP optimization of excited spin states and TDDFT calculations, highlight a change in the electronic and/or spin state due to the irradiation of the complexes.

V2O5/Ti3C2 MXene-Based Solid-State Passively Mode-Locked Tm:YAP laser at 2 μm

In the present work, V2O5/Ti3C2 MXene hybrid nanomaterials were successfully synthesized. The morphology and structure of the prepared V2O5/Ti3C2 MXene were investigated, and the results showed excellent bonding and strong interaction between Ti3C2 MXene and V2O5 nanoparticles. The nonlinear absorption properties of V2O5/Ti3C2 MXene nanocomposites at 2 μm have been investigated using power transfer techniques, and the large modulation depth of the material gives it potential for applications in nonlinear optics. As a result, a 2 μm solid-state mode-locked pulsed laser with V2O5/Ti3C2 MXene as a saturable absorber has been realized for the first time, generating a pulsed laser output as short as 657 ps, which corresponds to an average output power of 0.67 W. The results show that the synthesized V2O5/Ti3C2 MXene hybrid nanomaterials, which have a large optical nonlinearity, can be applied to generating an ultrashort 2 μm pulsed laser.

Pulsed Ho:YLF laser intra-cavity pumped by a diode-pumped Q-switched Tm:YAP laser.

We reported an intra-cavity pumped Q-switched laser with dual-wavelength synchronous output at 2066.7 nm and 1940nm. Ho:YLF crystal was pumped by a self-Q-switched Tm:YAP laser, which was served as both a gain medium and a saturable absorber simultaneously. For Ho:YLF laser, under 11.4-W incident pump power, a stable pulse laser was achieved at 2066.7 nm with the highest peak power of 69.65 W and the pulse repetition rate of 42.14 kHz. Under the same incident pump power, the highest peak power and pulse repetition rate of Tm:YAP laser were 17.85 W and 50.82 kHz, corresponding to the central wavelength of 1940nm. These results suggested that Q-switching without additional absorber element were effective way to obtain high-efficiency and compact 2.1 µm pulsed laser.

Laser induced temperature-jump time resolved IR spectroscopy of zeolites.

Combining pulsed laser heating and time-resolved infrared (TR-IR) absorption spectroscopy provides a means of initiating and studying thermally activated chemical reactions and diffusion processes in heterogeneous catalysts on timescales from nanoseconds to seconds. To this end, we investigated single pulse and burst laser heating in zeolite catalysts under realistic conditions using TR-IR spectroscopy. 1 ns, 70 μJ, 2.8 μm laser pulses from a Nd:YAG-pumped optical parametric oscillator were observed to induce temperature-jumps (T-jumps) in zeolite pellets in nanoseconds, with the sample cooling over 1-3 ms. By adopting a tightly focused beam geometry, T-jumps as large as 145 °C from the starting temperature were achieved, demonstrated through comparison of the TR-IR spectra with temperature dependent IR absorption spectra and three dimensional heat transfer modelling using realistic experimental parameters. The simulations provide a detailed understanding of the temperature distribution within the sample and its evolution over the cooling period, which we observe to be bi-exponential. These results provide foundations for determining the magnitude of a T-jump in a catalyst/adsorbate system from its absorption spectrum and physical properties, and for applying T-jump TR-IR spectroscopy to the study of reactive chemistry in heterogeneous catalysts.

Gain-switched 3 μm dysprosium-doped fluoride fiber laser pumped at 1.7 μm

To the best of our knowledge, we demonstrated a gain-switched 3 μm dysprosium-doped fluoride fiber laser pumped by a 1706.5 nm pulsed thulium-doped fiber master oscillator power amplifier for the first time. The maximum average power of the 3 μm pulsed laser was 50 mW with a slope efficiency of 12.3%, a repetition rate of 100 kHz, and a pulse width of 283 ns. This work exhibits the potential of 1.7 μm pulse pumped dysprosium-doped fluoride fiber laser as a platform for developing pulsed sources in the 3 μm region.

Mode-locked thulium/holmium-doped fiber laser utilizing manganese violet saturable absorber

2 µm pulsed lasers have slowly gathered attention over the years for their promising potential in the medical field and sensing. We report the fabrication of a saturable absorber (SA) made by coating manganese violet (MV) on an arc-shaped fiber and the successful utilization of this SA to generate mode-locked pulses in a thulium/holmium-doped fiber laser (THDFL). This is the first demonstration of mode-locking by using MV as a saturable absorber. The MV was first synthesized using hydrothermal method and then drop-casted onto a homemade arc-shaped fiber. The generated mode-locked pulses have a center wavelength of 1908.9 nm, a fundamental repetition rate of 12.27 MHz and a pulse width of 1.27 ps. The maximum output power of the laser was measured as 3.02mW with a slope efficiency of 1.36 %. The calculated pulse energy and the peak power are 246 pJ and 193.7 W, respectively. This work demonstrates the potential of MV, which belongs to the family of ammonium metal phosphates, as a saturable absorber used for mode-locked laser operations in the 2 µm region.

Development of a 2 μm Solid-State Laser for Lidar in the Past Decade.

The 2 μm wavelength belongs to the eye-safe band and has a wide range of applications in the fields of lidar, biomedicine, and materials processing. With the rapid development of military, wind power, sensing, and other industries, new requirements for 2 μm solid-state laser light sources have emerged, especially in the field of lidar. This paper focuses on the research progress of 2 μm solid-state lasers for lidar over the past decade. The technology and performance of 2 μm pulsed single longitudinal mode solid-state lasers, 2 μm seed solid-state lasers, and 2 μm high power solid-state lasers are, respectively, summarized and analyzed. This paper also introduces the properties of gain media commonly used in the 2 μm band, the construction method of new bonded crystals, and the fabrication method of saturable absorbers. Finally, the future prospects of 2 μm solid-state lasers for lidar are presented.

The peculiar SHG behaviour of Co-5,10,15,20-tetraphenilporphyrinate in the solid state. An experimental and theoretical study

We prepared and investigated the SHG behavior in the solid state of the Cobalt 5,10,15,20-tetraphenylporphyrinate that crystallizes in the acentric I4¯2d space group. The compound was synthesized and characterized, and the Second Harmonic Generation (SHG) response of a powdered sample was measured through a 1.907 μm pulsed laser radiation. During laser irradiation, a gradual increase of the intensity of the SH signal was observed until, after a few minutes, it reached a plateau of about fifty times the initial value. We attempted to understand the origin of this peculiar SHG behavior, both through experimental analysis and theoretical calculations. Mass spectrometry, absorption, emission, and vibrational spectroscopies in solution combined with powder X-ray diffraction analysis in solid state, both before and after irradiation, do not evidence any chemical degradation, phase transition or amorphization process. Theoretical calculations on little fragments of the Co-TPP structure simulate appropriately the structural feature of the complex and its initial experimental SHG response. UV–VIS and EPR spectra collected in the solid state before and after irradiation, in conjunction with DFT/B3LYP optimization of excited spin states and TDDFT calculation, highlight a change in the electronic and/or spin state due to the irradiation of the complex.

Tellurium crystal pumped with ultrafast 10 µm pulses demonstrates a giant nonlinear optical response.

The nonresonant nonlinear optical response of bulk tellurium (Te) is studied using 220 fs 10 µm laser pulses with photon energy roughly three times smaller than the band gap energy. The Kerr nonlinearity is found to be extremely large (n2,eff = 3.0-6.0 × 10-12 cm2/W), nearly 100 times larger than that of GaAs, depending on crystal orientation. Multiphoton absorption is observed at intensities >109 W/cm2 indicating the importance of free carriers to the overall nonlinear optical response. The large values of the nonlinear susceptibilities of Te open up possibilities of designing thin film elements for mid- and long-wavelength infrared nonlinear photonics.

1.55 μm Narrow-Linewidth Pulsed Laser Based on MgO:PPLN

A high-power narrow-linewidth 1.55 μm pulsed laser, based on MgO:PPLN OPO, has been achieved using a F–P etalon. The pump source is a 1064 nm acousto-optical (AO) Q-switched Nd:YAG laser with a repetition rate of 10 kHz. Under the maximum pump power of 18 W, the signal output power of 2.57 W is demonstrated at 1551.1 nm with a linewidth of 0.07 nm, corresponding to a slope efficiency of 16.1%. Different from traditional inversion lasers, the narrow-linewidth wavelength tunability of approximately 1.55 μm can be realized by changing the temperature.

Nanometer-Thin Stacks of MXenes (Ti3C2Tx and Ta4C3Tx) for Applications as Nonlinear Photonic Devices

Two-dimensional (2D) carbides of transition metals, so called “MXenes”, maintain excellent optical properties and unique layer stacking form via hydrogen bonds in contrast to other low-dimensional materials. These promising features have attracted increasingly research interest in the field of ultrafast photonics. In this work, titanium carbide (Ti3C2Tx) and tantalum carbide (Ta4C3Tx), as two promising MXene materials for photonic applications, are experimentally synthesized by the ultrasound-assisted liquid phase exfoliation technique. The morphology of prepared few-layer Ti3C2Tx and Ta4C3Tx has been systematically characterized by transmission electron microscopy and X-ray diffraction analysis. Density functional theory is performed to obtain their electronic band structures, demonstrating metallic properties and verifying their optical absorption at 1 μm. Their tempting optical modulation properties for multi-gigahertz pulsed laser emission are demonstrated by using them as saturable absorbers in a waveguide laser cavity. Particularly, high-performance Q-switched mode-locked lasers with/without laser mirrors are realized based on the hybrid waveguide laser configuration, delivering 1 μm laser pulses with durations as short as 30 ps. The results presented in this work show the great potential of metallic MXenes and waveguide structures for applications in functional photonic devices.

Ultra-broadband pulse generation via hollow-core fiber compression and frequency doubling for ultra-intense lasers

Abstract We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification, hollow-core fiber (HCF) and second harmonic generation processes. In this setup, the spectrum of an approximately 1.8 μm laser pulse has near 1 μm full bandwidth by employing an argon gas-filled HCF. Subsequently, after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair, 9.6 fs (~3 cycles) and 150 μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated. The energy stability of the output laser pulse is excellent with 0.8% (root mean square) over 20 min, and the temporal contrast is >1012 at –10 ps before the main pulse. The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.

Investigation of parameters affecting the high harmonic generation from monolayer WS2

AbstractThe effect of crystal symmetry in the high harmonic generation of monolayer WS2 is investigated using the three‐dimensional time‐dependent density functional theory. The role of linearly and elliptically polarized laser, as well as the crystall orientation in the enhancement of harmonics yield, is explored. Also, the wavelength dependence of the harmonic yield and the intensity dependence of cutoff harmonic order are studied. The former shows an exponential decay with increasing the driving laser wavelength, and the latter reveals a linear dependency of cutoff harmonic to the driving laser field. Moreover, a dual pulse system as a driving laser, a fundamental 1.3 μm laser pulse synthesized by its second harmonic, is proposed which could increase the cutoff harmonic order up to 24th (22 eV). Our results pave the way for controlling and enhancing high harmonic spectra from solids.

Matlab-based gain modeling and simulation of a 1300-1400 nm wavelength band neo-doped fiber amplifier

A systematic investigation of gain-modulated neodymium-doped fiber laser is carried out. The numerical model of gain modulated thulium-doped neodymium fiber laser oscillator and amplifier is constructed based on the rate equation and transmission equation, and solved by the time domain finite difference method. The nano-second laser output in the 2 μm band with high conversion efficiency, narrow linewidth, and single polarization was obtained by numerical simulation. A 2 μm pulsed laser output with a maximum power of 340 mW and amplification of 42 dB was obtained using a master oscillator, and a 2 μm pulsed laser output with a maximum power of 9.13 W was obtained using a power amplifier. The model can be used as a reference for experimental research and engineering design of this type of laser.

Stimulated Thermal Scattering in Two-Photon Absorbing Nanocolloids under Laser Radiation of Nanosecond-to-Picosecond Pulse Widths.

Recent discoveries in nonlinear optical properties of nanoparticle colloids make actual the challenge to lower the energy threshold of phase conjugation and move it into the domain of shorter pulse widths. A novel effect of the stimulated Rayleigh-Mie scattering (SRMS) in two-photon absorbing nanocolloids is considered as a promising answer to this challenge. We report the results of experimental and theoretical study of the two-photon-assisted SRMS in Ag and ZnO nanocolloids in the nanosecond-to-picosecond pulse width domain. For 12 ns 0.527 μm laser pulses, the four-wave mixing SRMS scheme provides lasing and amplification of backscattered anti-Stokes signal in Ag nanocolloids in toluene at the threshold 0.2 mJ and the spectral shifts up to 150 MHz. For 100 ps 0.532 μm pulses, we observed for the first time efficient (over 50% in signal-to-pump ratio of pulse energies) SRMS backscattering of the anti-Stokes signal in Ag nanocolloids in toluene and predominantly Stokes signal in ZnO nanocolloids in water, with the spectral shifts up to 0.25 cm−1. We develop the first order-in-perturbation model of the four-wave mixing two-photon absorption-assisted SRMS process which shows that at nanosecond pulses, amplification is predominantly due to the thermal-induced coherent oscillations of polarization while the slow temperature wave acts also as a dynamic spatial grating which provides a self-induced optical cavity inside the interaction region. At a picosecond pulse width, according to our model, the spectral overlap between pump and signal pulses results in formation of only the dynamic spatial temperature grating, and we succeeded at recovering the linear growth of the spectral shift with the pump power near the threshold.

Self-Q-switched Tm:YAP vortex laser by thermal-lensing effect

We demonstrated a self-Q-switched Gaussian laser mode and a Laguerre-Gaussian (LG0,1) laser mode at 1937.9 nm, which was directly generated by thermal lensing effect in a Tm:YAP laser. By building a Mach-Zehnder interferometer, the helical nature of the wavefront is checked. The experimental maximum output power of LG01 pulsed vortex laser was 83 mW with the repetition rate of 75.46 kHz and pulse width of 1.711 μs, corresponding to the peak power of 0.64 W and single pulse energy of 1.10 μJ. The self-Q-switched Tm:YAP vortex laser is compact and provides a convenient way to construct 2 μm pulsed vortex laser source.

Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO2 laser

Understanding the formation and long-timescale evolution of atmospheric plasmas produced by ultrashort, long-wavelength infrared (LWIR) pulses is an important but partially understood problem. Of particular interest are plasmas produced in air with a peak laser intensity ∼1012 W/cm2, the so-called clamping intensity observed in LWIR atmospheric guiding experiments where tunneling and multi-photon ionization operative at near-IR or shorter wavelengths are inoperative. We find that avalanche breakdown on the surface of aerosol (dust) particles can act to seed the breakdown of air observed above the 200 GW/cm2 threshold when a train of 3 ps 10.6 μm laser pulses separated by 18 ps is used. The breakdown first appears at the best focus but propagates backward toward the focusing optic as the plasma density approaches critical density and makes forward propagation impossible. The velocity of the backward propagating breakdown can be as high as 109 cm/s, an order of magnitude greater than measured with ns pulse-produced breakdown, and can be explained rather well by the so-called breakdown wave mechanism. Transverse plasma expansion with a similar velocity is assisted by UV photoionization and is observed as a secondary longitudinal breakdown mechanism in roughly 10% of the shots. When a cm-size, TW power beam is propagated, interception of aerosol particles is guaranteed and several (40 cm−3) breakdown sites appear, each initially producing a near-critical density plasma. On a 10 ns–1 μs timescale, shockwaves from each site expand radially and coalesce to produce a large hot gas channel. The radial velocity of the expansion agrees well with the prediction of the blast wave theory developed for ultrafast atmospheric detonations.

In-band pumped 2 μm pulsed laser with dual-wavelength synchronous output

We reported an in-band pumped Q-switched laser with dual-wavelength synchronous output at 2067.1 nm and 1885.7 nm. Ho:YLF crystal, which was pumped by Tm:YLF laser, was served as both a gain medium and a saturable absorber simultaneously. For Ho:YLF laser, under 16.02 W incident pump power, a stable pulse laser was achieved at 2067.1 nm with the highest peak power of 21.71 W and the pulse repetition rate of 70.62 kHz. Under the same incident pump power, the highest peak power and pulse repetition rate of Tm:YLF laser were 44.05 W and 71.56 kHz corresponding to the central wavelength of 1881.5 nm. These results suggested that in-band pumping was an effective way to obtain high efficiency dual-wavelength synchronous pulsed laser.

Shot-noise limited homodyne detection for MHz quantum light characterisation in the 2 µm band.

Characterising quantum states of light in the 2 µm band requires high-performance shot-noise limited detectors. Here, we present the characterisation of a homodyne detector that we use to observe vacuum shot-noise via homodyne measurement with a 2.07 µm pulsed mode-locked laser. The device is designed primarily for pulsed illumination. It has a 3-dB bandwidth of 13.2 MHz, total conversion efficiency of 57% at 2.07 µm, and a common-mode rejection ratio of 48 dB at 39.5 MHz. The detector begins to saturate at 1.8 mW with 9 dB of shot-noise clearance at 5 MHz. This demonstration enables the characterisation of megahertz-quantum optical behaviour in the 2 µm band and provides a guide of how to design a 2 µm homodyne detector for quantum applications.