Tie-Jun Wang

• PhD
• Group Leader at Shanghai Institute of Optics and Fine Mechanics

The conventional use of Laser‐Induced Breakdown Spectroscopy (LIBS) for elemental analysis in high‐density polyethylene (HDPE) limits the exploration of bond behavior in Physics and Chemistry. A suitable combination of process parameters, exceeding the bond dissociation threshold, enables LIBS to break HDPE bonds, facilitating laser‐induced pyrolys...

Third harmonic generation (THG) by laser filamentation in gases is immune to the damage threshold and phase matching limit for UV and EUV pulse generation. Here, we report on the jitter measurements of the beam pointing and the intensity of the THG through filamentation with different repetition rates in air. The THG jitters are stronger at the hig...

The emission of N2⁺ lasing at 391 nm from 800 nm femtosecond laser filament in air at 1 atm presents significant challenges due to the quenching effect induced by oxygen molecules. We introduce a simple technique for the 391 nm N2⁺ lasing emission induced by a corona electric field-assisted femtosecond filament in air. This technique greatly addres...

The evolution of the THz waveform generated from the two-color air filament was experimentally investigated by moving an iris along the plasma channel. By taking the differentiation of the measured THz waveforms, the local longitudinally resolved THz waves along a 54 mm-long filament were obtained. The local THz pulse underwent periodic phase shift...

Laser-induced breakdown spectroscopy (LIBS) is a commonly employed technique in commercial plastic recycling for purposes including classification, sorting, identification, and elemental analysis. However, understanding the molecular-level kinetics, thermodynamic interactions, bonding cleavage, and process parameter impacts is crucial for identify...

The femtosecond laser filamentation is of significant interest due to its remarkable characteristics, and determining the critical power of self-focusing is essential for the process of filamentation. In this work, the critical power for self-focusing of intense femtosecond laser pulses at different repetition rates is experimentally measured accor...

The evolution of THz waveform generated from the two-color air filament was experimentally investigated by moving an iris along the plasma channel. By taking the differentiation of the measured THz waveforms, the longitudinally resolved THz waves along 54 mm long filament were obtained. The local THz pulse undergoes periodic phase shifts. Theoretic...

Supercontinuum (SC) light source has advanced ultrafast laser spectroscopy in condensed matter science, biology, physics, and chemistry. Compared to the frequently used photonic crystal fibers and bulk materials, femtosecond laser filamentation in gases is damage-immune for supercontinuum generation. A bottleneck problem is the strong jitters from...

The characteristics of plasmas play an important role in femtosecond laser filament-based applications. Spectroscopic analysis is used to experimentally investigate the plasma density and its temperature of the air filament under different pulse repetition rates. In our experiments, the measured average plasma density of the filament is 1.54 × 10 1...

Cloud electrification is one of the oldest unresolved puzzles in the atmospheric sciences. Though many mechanisms for charge separation in clouds have been proposed, a quantitative understanding of their respective contribution in a given meteorological situation is lacking. Here we suggest and analyze a hitherto little discussed process. A qualita...

The evolution of THz waveform and frequency generated from the two-color air filament was experimentally investigated by moving an iris along the filament. With the increase of the filament length, the peak-to-peak amplitude of THz signal existed an oscillating behavior which is attributed to the relative phase between the two-color laser pulses an...

The evolution of THz waveform and frequency generated from the two-color air filament was experimentally investigated by moving an iris along the filament. With the increase of the filament length, the peak-to-peak amplitude of THz signal existed an oscillating behavior which is attributed to the relative phase between the two-color laser pulses an...

Achieving optically controlled nanomachine engineering can satisfy the touch-free and non-invasive demands of optoelectronics, nanotechnology, and biology. Traditional optical manipulations are mainly based on optical and photophoresis forces, and they usually drive particles in gas or liquid environments. However, the development of an optical dri...

Discharges of different polarities develop in different modes, resulting in different guiding effects by femtosecond laser filaments. Knowledge of the contribution of laser filaments to positive and negative discharges is the basis of the laser-guided long-air-gap discharge technique. This study presents a direct comparison of the inception, propag...

As intense, ultrashort, kHz-repetition-rate laser systems become commercially available, pulse cumulative effects are critical for laser filament-based applications. In this work, the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally. The pulse repetition-rate effect has negl...

We experimentally demonstrated the 3D propagation of laser filament in air by an Fabry-Pérot (F-P) cavity assisted imaging within a single exposure. The F-P cavity was composed of two parallel mirrors with certain reflectivity and transmission at filament laser, so that the beam was reflected and refracted multiple times between the two mirrors. Th...

Cumulative effects are crucial for applications of laser filaments, such as for the remote transfer of energy and the control of electric discharges. Up to now, studies of cumulative effects in the air of high-repetition-rate pulse trains have been performed at lower rates than 10 kHz. Herein, the nonlinear effects associated with short plasma fila...

We experimentally demonstrated the 3D propagation of laser filament in air by an Fabry-Pérot (F-P) cavity assisted imaging within a single exposure. The F-P cavity was composed of two parallel mirrors with certain reflectivity and transmission at filament laser, so that the beam was reflected and refracted multiple times between the two mirrors. Th...

We experimentally demonstrated the 3D propagation of laser filament in air by an Fabry-Pérot (F-P) cavity assisted imaging within a single exposure. The F-P cavity was composed of two parallel mirrors with certain reflectivity and transmission at filament laser, so that the beam was reflected and refracted multiple times between the two mirrors. Th...

A piecewise diffraction calculation model based on scalar diffraction theory was proposed to simulate the propagation of probe beam in the same direction as the filament. Based on this model the diffraction rings of the detected light recorded in the experiment were fitted. The results show that the segmented diffraction model can extend the measur...

Analytical expressions for the cross-spectral density matrix of a partially coherent twisted Laguerre-Gaussian pulsed (PCTLGP) beam in anisotropic atmospheric turbulence are derived based on the extended Huygens–Fresnel principle. Numerical results indicate that the atmospheric turbulence induces the degeneration of the spectral intensity distribut...

The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method. A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser...

We have extended the photocurrent model on THz radiation generation from an external DC electric field biased and single-color femtosecond laser induced Ar-gas micro-plasma. The properties of THz radiation under different conditions have been analyzed. The simulation results show that the THz radiation from laser-induced plasma can be significantly...

The propagation of intense femtosecond laser pulses in atmospheric air can lead to a channel with high laser intensity, high plasma density, and capability for remote generation and control, namely filament. When the filaments interact with the materials, high laser intensity can excite the materials and induce the finger print fluorescence of the...

Laser polarization and its intensity inside a filament core play an important role in filament-based applications. However, polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related fila-mentation phenomena. Here, we report on experimental and numerical investigations of polarization depend...

We experimentally investigate the laser polarization effect on the supercontinuum (SC) generation through femtosecond laser filamentation in air. By tuning filamenting laser ellipticity from linear polarization to circular polarization, the spectral intensity of the SC after filamentation gradually increases, while the spectral bandwidth of the SC...

Supercontinuum (SC) light source has advanced ultrafast laser spectroscopy in condensed matter science, biology, physics, and chemistry. Compared to the frequently used photonic crystal fibers and bulk materials, femtosecond laser filamentation in gases is damage-immune for supercontinuum generation. A bottleneck problem is the strong jitters from...

Modulation and direct measurement of the radial fluence distribution inside a single filament core (especially less than 100 μm in diameter) is crucial to filament-based applications. We report direct measurements of the radial fluence distribution inside a femtosecond laser filament core and its evolution via the filament-induced ablation method....

We report on the experimental investigation of femtosecond laser filament guided negative coronas. When the coupling between the filament and negative corona was weak, the side fluorescence spectral analysis confirmed the existence of impact ionization although less effect on the filament length was observed. When the coupling was strong so that th...

Polarization dependence on clamping intensity inside femtosecond filament was experimentally measured in air. By tuning the laser pulse ellipse from linear polarization to circular polarization, the measured clamping intensity inside laser filament is gradually increased up to 1.7 times. The experimental results are in good agreement with the simul...

We compare detailed spatio-temporal propagation simulations with experiments on generation of terahertz (THz) pulses in single filaments with two-color optical excitation, which elucidates the mechanism whereby positively chirped optical pulses lead to the maximum THz yield. The long-wavelength components in the leading edge of the positively chirp...

AgI-type pyrotechnics are widely used in the field of weather modification, as a kind of artificial ice nuclei. However, their precipitation yield remains an intensively studied area. In this paper, we present a study of AgI-type pyrotechnic nucleant-induced water condensation promoted by femtosecond laser filaments in a cloud chamber. It is found...

We report on a method to experimentally generate ionic wind by coupling an external high voltage electric field with an intense femtosecond laser induced air plasma filament. The measured ionic wind velocity could be as strong as >4 m/s. It could be optimized by changing the applied electric field and the laser induced plasma channel. The experimen...

Based upon experimental observation in the laboratory, we propose that ionic wind from corona discharge inside a thundercloud would play an important role in producing a rain gush. A cyclic chain of events inside a super-saturated environment in a thundercloud is proposed, each event enhancing the successive ones until lightning occurs. These succe...

We report on a systematic study of the laser polarization effect on a femtosecond laser filamentation in air. By changing the laser's ellipticity from linear polarization to circular polarization, the onset position of laser filament formation becomes farther from the focusing optics, the filament length is shorter, and less laser energy is deposit...

Sub-picosecond chirped laser pulse-induced airflow and water condensation were investigated in a cloud chamber. The results indicate that the positively chirped sub-picosecond laser pulses generate a more uniform intensity distribution inside the plasma column, leading to a weaker airflow and an elliptic-shaped snow pile. The negatively chirped sub...

We demonstrate a simple technique to filter out the continuum background in filament-induced remote breakdown spectroscopy. By inserting a polarizer before the detector, the continuum background was reduced by more than 42% in filament-induced breakdown spectroscopy at a distance of 3.8 m, while the fluorescence intensity of aluminum atomic lines r...

Water condensation and precipitation induced by 22-TW 800-nm laser pulses at 1 Hz in an open cloud chamber were investigated in a time-resolved manner. Two parts of precipitation in two independent periods of time were observed directly following each laser shot. One part started around the filament zone at t < 500 μs and ended at t 1.5 ms after th...

We report on a method to experimentally generate ionic wind by coupling an external high voltage electric field with an intense femtosecond laser induced air plasma filament. The measured ionic wind velocity could be as strong as >4 m/s. It could be optimized by changing the applied electric field and the laser induced plasma channel. The experimen...

Artificial rainmaking is in strong demand especially in arid regions. Traditional methods of seeding various Cloud Condensation Nuclei (CCN) into the clouds are costly and not environment friendly. Possible solutions based on ionization were proposed more than 100 years ago but there is still a lack of convincing verification or evidence. In this r...

An optimization design scheme is proposed for the femtosecond laser induced corona discharge experiment. The differences between spherical electrode and traditional cone electrode are investigated by numerical analysis. The distribution of space electric field around femtosecond filament is demonstrated, and the thresholds of corona electric field...

We observe the third-harmonic generation and second-harmonic generation together with element fluorescence from the interaction of a femtosecond laser filament with a rough surface sample (sandy soil) in non-phasematched directions. The harmonics prove to originate from the phase-matched surface harmonics and air filament, then scatter in non-phase...

We report on a waveform control of enhanced THz radiation along a femtosecond laser filament in air with a high voltage technique. By applying a DC high-voltage electric field from two sharp electrodes in a direction parallel to the laser filament and scanning it along the filament, the longitudinal evolution of amplified THz emission was demonstra...

We present a novel method based on plasma-guided corona discharges to probe the plasma density longitudinal distribution, which is particularly good for the weakly ionized plasmas (~10¹⁴ cm⁻³). With this method, plasma density longitudinal distribution inside both a weakly ionized plasma and a filament were characterized. When a high voltage electr...

We investigated water condensation in a laboratory cloud chamber induced by picosecond (ps) laser pulses at ~350 ps (800 nm/1–1000 Hz) with a maximum peak power of ~25 MW. The peak power was much lower than the critical power for self-focusing in air (~3–10 GW depending on the pulse duration). Sparks, airflow and snow formation were observed under...

We demonstrated for the first time the condensation and precipitation (or snowfall) induced by a corona discharge inside a cloud chamber. Ionic wind was found to have played a more significant role than ions as extra Cloud Condensation Nuclei (CCN). 2.25 g of net snow enhancement was measured after applying a 30 kV corona discharge for 25 min. In c...

A unified picture of femtosecond laser induced precipitation in a cloud chamber is proposed. Among the three principal consequences of filamentation from the point of view of thermodynamics, namely, generation of chemicals, shock waves and thermal air flow motion (due to convection), the last one turns out to be the principal cause. Much of the fil...

We investigated femtosecond laser-filamentation-induced airflow, water condensation and snow formation in a cloud chamber filled respectively with air, argon and helium. The mass of snow induced by laser filaments was found being the maximum when the chamber was filled with argon, followed by air and being the minimum with helium. We also discussed...

We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona discharge (CD). Fluorescence spectra from neutral and ionic air molecules were measured and compared with pure high-voltage CD and pure la...

We report on the experimental observation of the airflow motion induced by an 800 nm, 1 kHz femtosecond filament in a cloud chamber filled with air and helium. It is found that vortex pairs with opposite rotation directions always form both below and above the filaments. We do not observe that the vortices clearly formed above the filament in air j...

Lasing action inside a femtosecond laser filament in air has recently attracted much attention due to its important application on enhanced remote sensing. In this chapter, we summarize our recent experimental work together with physical understanding on various lasing actions inside femtosecond laser filaments in air, namely, amplified spontaneous...

Airflow induced by femtosecond laser (800 nm/1 kHz/25 fs) filamentation with different lengths was investigated in a laboratory cloud chamber. Various filament lengths were generated by adjusting laser energy and lens focal length. It was found that airflow patterns are closely related to filament intensity and length. Intense and long filaments ar...

Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reporte...

We report on a longitudinally resolved measurement of plasma density along femtosecond laser filament in air via needlelike high-voltage DC electric field enhanced THz spectroscopy. Longitudinal distribution of plasma density of ~1015 cm-3 along laser filament has been successfully recorded.

The polarization evolution and control of a femtosecond laser pulse in the wake of molecular alignment inside a laser filament was investigated. A weak probe pulse was delayed with respect to the field-free revivals of the pre-excited rotational wave-packets created by an infrared filamenting pulse in nitrogen gas. 30° was set between the pump and...

We report on a longitudinally resolved measurement of plasma density along femtosecond laser filament in air via needlelike high-voltage DC electric field enhanced THz spectroscopy. Longitudinal distribution of plasma density of ~1015 cm-3 along laser filament has been successfully recorded.

Calculation of the saturation ratio inside vortices formed below the filament in a sub-saturation zone in a cloud chamber was given. By mixing the air with a large temper-ature gradient, supersaturation was sustained inside the vor-tices. This led to precipitation and snow formation when strong filaments were created using short focal length lenses...

We report on a longitudinally resolved measurement of plasma density along femtosecond laser filament in air via terahertz (THz) spectroscopy. By applying a needlelike high-voltage direct current (DC) electric field on the laser filament and scanning it along filament, the longitudinal evolution of amplified THz emission has been demonstrated. The...

Strong fluorescence emissions from nitrogen monohydride (NH) free radical at 336 nm were observed in air, when water vapor was present in a 400 nm femtosecond laser filament. The generated NH radical is ascribed to chemical reaction between nitrogen and water vapor during laser filamentation. The backscattered fluorescence from NH shows an exponent...

1 kHz, 2 mJ, 45 fs, 800 nm laser pulses were fired into a laboratory diffusion cloud chamber through a subsaturated zone (relative humidity ∼73%, T ∼ 4.3 °C). After 60 min of laser irradiation, an oval-shaped snow pile was observed right below the filament center and weighed ∼12.0 mg. The air current velocity at the edge of the vortices was estimat...

White-light seeded forward lasing action from a femtosecond laser filament in air was systematically investigated. Using the self-generated white-light seed from 800-and 400-nm laser filaments, 428-and 391-nm lasings, respectively, were observed. When an external white-light seed produced from a femtosecond laser supercontinuum in a water cell was...

We have demonstrated experimentally that firing a laser filament in a subsaturated zone of a cloud chamber of inversed temperature profile could induce water condensation. Initially, through ion chromatography performed on samples collected from a receptacle placed under the laser, the presence of HNO 3 was observed. The existence of this HNO 3 , a...

428 nm forward lasing action was observed from a femtosecond laser filament in air created by Ti:sapphire laser pulses. The 800 nm femtosecond laser filament not only provides a source for population inversion between two vibrational levels (B26C u .0/ and X26C g .1/) of NC2 but also generates a 428 nm seed from filament-induced white light. This s...

We have demonstrated experimentally that firing a laser filament in a subsaturated zone of a cloud chamber of inversed temperature profile could induce water condensation. Initially, through ion chromatography performed on samples collected from a receptacle placed under the laser, the presence of HNO 3 was observed. The existence of this HNO 3 , a...

The water vapor fluorescence in air from filaments generated by intense ultrashort Ti:sapphire laser pulses is experimentally studied. The backscattered fluorescence from OH shows an exponential increase with increasing filament length, indicating amplified spontaneous emission. By measuring the intensity inside the filament and the fluorescence in...