Laser-induced Breakdown In Water Research Articles

High-Conversion Efficiency Pulse Compression by Stimulated Raman Scattering and Laser Induced Breakdown in Water

A novel temporal pulse compression technique, combining stimulated Raman scattering (SRS) and laser induced breakdown (LIB) principles was presented in this work, which employing an energy controllable dual-cell setup. As a novel type of plasma shutter, the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell was used to transmit the high-power peak at the leading pulse edge and successfully block its low-power tail. The effect resulted in a 7 ns pulse duration from a Nd: YAG laser compressed into 330 ps, the pulse compression ratio was about 21×. The magnified optical power of the leading edge diminished the threshold of SRS and improved the beam quality of the output pulse. In addition, the output energy of Stokes was approximately 2 times than that of the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> cell process, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell process increased the energy conversion efficiency from 4.2% to 15.8%. Thus, the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> -order Stokes SRS was greatly improved, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order Stokes SRS was more easily generated. The method provided a simple but convenient way to generate a short pulse with a high energy conversion efficiency Raman laser.

Estimating the effective pressure from nanosecond laser-induced breakdown in water.

Nanosecond laser-induced breakdown (LIB) in liquids (e.g., water) can produce dynamic high pressure and high temperature. However, since high pressure needs to negate the effect of high temperature to some degree, it is only partially effective. As a result, it is difficult to directly measure the effective pressure due to the transient and complex LIB process. Here, we presented a simple method based on Raman spectroscopy to indirectly determine the effective pressure caused by LIB in liquid pure H2O and low concentration H2O-H2O2 mixtures. By comparing the Raman shifts of the ice-VII mode for pure H2O and H2O-H2O2 mixtures under laser pumping and static high pressure, the LIB effective pressure can be first estimated. The empirical equation was then derived base on the correlation of the LIB effective pressure to ice-VII-point stimulated Raman scattering thresholds for pure and mixture water solutions, which can be used to estimate the LIB effective pressures for other different mixture water solutions with the uncertainty of 0.14-0.25 Gpa. Hopefully, our study here would advance the measurements of effective pressure in the LIB process.

Experimental research on plastic deformation of metal foil through ns laser-induced mechanical effects underwater

Laser shock forming (LSF) is an effective method to induce plastic deformation of metal foil, but the need for a solid-state energy absorbent layer during LSF limits its engineering application. Strong shockwave can also be launched by laser-induced breakdown in water because of the nonlinear absorption of water. So through this method, underwater laser-induced mechanical forming (LMF) without specialized absorbent layer can be achieved. In this paper, nanosecond laser was used to induce the breakdown of water. The feasibility of inducing metal foil plastic deformation through LMF with water as the absorbent layer was validated. The surface morphology of the obtained micro pit on the metal foil was observed and measured by a topography measuring instrument and a scanning electron microscope. The laser-induced shockwave and the process of forming bubbles were recorded by a high speed camera. It is found that there are three possible mechanisms responsible for the plastic deformation of metal foil underwater: water-breakdown-induced shockwave, bubble-pulsation-induced shockwave and bubble-collapse-induced micro jet. The dominant forming mechanism and the forming result can be controlled by changing the distance between the laser focus and the foil surface.

Optical Fiber Fabry-Perot Interferometer Sensor Fabricated by Femtosecond Laser-Induced Water Breakdown

The Fabry-Perot interferometer sensor in the optical fiber fabricated by femtosecond laser in the water is investigated in this article. The Fabry-Perot interferometer fabricated with different laser pulse energies and cavity lengths are discussed in the air and water. It is concluded that the Fabry-Perot interferometer with 60 mW in the water has more obvious fringe visibility, and the method has high potentials in Fabry-Perot interferometer fabrication.

High-speed photography of shock waves with an adaptive illumination.

An adaptable, laser-diode-based illumination system was developed to simultaneously visualize the dynamics of slow and fast phenomena in optically transparent media. The system can be coupled with still or high-speed cameras and makes it possible to generate an arbitrary train of illumination pulses with a variable pulse duration, pulse energy, and an intrapulse delay with a temporal resolution of 12.5 ns. Its capabilities are presented with selected illustrative visualizations of the dynamics of the shock waves and the cavitation entities generated after the laser-induced breakdown in water.

Mach–Zehnder interferometer based on a cross-type microchannel in SMS fiber structure for gas pressure sensing with high sensitivity

An inline fiber Mach–Zehnder interferometer (MZI) based on a cross-type microchannel in single mode–multimode–single mode fiber structure was proposed. The cross-type microchannel was fabricated in the fiber material directly using femtosecond laser-induced breakdown in water. The horizontal part of the cross-type microchannel along the fiber direction results in enough phase difference for the interference, and the cross-type shape makes the whole structure more robust because a smaller part of fiber material is etched. In addition, the proposed MZI shows high-pressure sensitivity (−14.27 nm / MPa), low-temperature cross sensitivity (0.043 nm/°C), and low strain force cross sensitivity (0.257 nm/N), which makes it a promising candidate for applications in gas pressure sensing field.

Spectroscopic features of laser-induced breakdown in water and aqueous solutions in ultrasonic field

It is established that the action of ultrasound leads to both sharp enhancement of the acoustic emission and increase in the intensity of spectral lines of laser-excited elements dissolved in aqueous salt solutions (NaCl, NaHCO3, CaCl2), which provides a new method of combined laser–ultrasonic spark spectroscopy. The task of synchronization of the acoustic and optical emission has been solved, which reveals dependence of the intensity of spectral lines on the phase of ultrasonic wave action.

Water-assisted femtosecond laser micromachining of micro-cavities in optical fiber

ABSTRACTThe micro-cavities in the optical fiber by femtosecond laser direct writing in the water is investigated in this paper. The micro-cavity fabricated under different conditions such as laser pulse energies and translation speeds are discussed, and the optimal parameters are investigated for a particular application. The method of femtosecond laser induced water breakdown provided an alternative solution for high quality micro-structure fabrication.

High-quality Mach-Zehnder interferometer based on a microcavity in single-multi-single mode fiber structure for refractive index sensing.

A fiber inline Mach-Zehnder interferometer (MZI) based on a microcavity with two symmetric openings in single-multi-single mode fiber (SMSF) structure is proposed. By using the finite difference beam propagation method (FD-BPM), the interference spectrum simulation result shows that the MZI can still have high-quality interference even if the microcavity deviates along the radial direction for 3 μm. Therefore, it allows a larger fabrication tolerance and tremendously decreases the fabrication difficulty. Then a microcavity with two symmetric openings in SMSF was fabricated by using femtosecond laser-induced water breakdown. The insertion loss of the microcavity immerged in water is only -8 dB, and the MZ interference peak contrast in the transmission spectrum reaches more than 30 dB. The MZI based on the microcavity in SMSF can be used as a practical liquid refractive index sensor as its high-quality interference spectrum, ultrahigh sensitivity (9756.75 nm/RIU), high refractive index resolution (2×10-5 RIU), good linearity (99.93%), and low-temperature crosstalk (0.04 nm/°C).

Wavelength dependence of femtosecond laser-induced breakdown in water and implications for laser surgery

The wavelength dependence of the threshold for femtosecond optical breakdown in water provides information on the interplay of multiphoton, tunneling, and avalanche ionization and is of interest for parameter selection in laser surgery. We measured the bubble threshold from ultraviolet to near-infrared wavelengths and found a continuous decrease of the irradiance threshold with increasing wavelength $\ensuremath{\lambda}$. Results are compared to the predictions of a numerical model that assumes a band gap of 9.5 eV and considers the existence of a separate initiation channel via excitation of valence band electrons into a solvated state followed by rapid upconversion into the conduction band. Fits to experimental data yield an electron collision time of $\ensuremath{\approx}1\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$ and an estimate for the capacity of the initiation channel. Using that collision time, the breakdown dynamics were explored up to $\ensuremath{\lambda}=2\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$. The irradiance threshold first continues to decrease but levels out for wavelengths longer than 1.3 $\ensuremath{\mu}\mathrm{m}$. This opens promising perspectives for laser surgery at wavelengths around 1.3 and 1.7 $\ensuremath{\mu}\mathrm{m}$, which are attractive because of their large penetration depth into scattering tissues.

Ultrasensitive liquid refractometer based on a Mach-Zehnder micro-cavity in optical fibre fabricated by femtosecond laser-induced water breakdown

A Mach–Zehnder (MZ) micro-cavity with two symmetric openings in single mode fibre (SMF) was fabricated by femtosecond laser-induced water breakdown. The micro-cavity is rightly across half of the fibre core, and the opening size of the micro-cavity is 10 μm × 100 μm. The micro-cavity and the remaining half of the fibre core constitute two arms of the Mach–Zehnder interferometer (MZI). The MZI with micro-cavity immerged in water shows perfect interference spectrum due to the regular shape and smooth internal surface of the micro-cavity. The insertion loss is only –8 dB and the contrast of one MZI peak reaches more than 40 dB. The MZI with micro-cavity in SMF can be used as an ultrasensitive liquid refractometer as its ultrahigh refractive index (RI) sensitivity (14296.98 nm/RIU), high RI resolution (1 × 10−5 RIU), good linearity (99.62%) and low temperature crosstalk (0.04 nm/°C).

Wavelength dependence of nanosecond infrared laser-induced breakdown in water: Evidence for multiphoton initiation via an intermediate state

Abstract : Investigation of the wavelength dependence (725 1025 nm) of the threshold for nanosecond optical breakdown in water revealed steps consistent with breakdown initiation by multiphoton ionization, with an initiation energy of about 6.6 eV. This value is considerably smaller than the autoionization threshold of about 9.5 eV, which can be regarded as band gap relevant for avalanche ionization. Breakdown initiation is likely to occur via excitation of a valence band electron into a solvated state, followed by rapid excitation into the conduction band. Theoretical analysis based on these assumptions suggests that the seed electron density required for initiating avalanche ionization drops from 2.51015 cm-3 at 725 nm to 1.11012 cm-3 at 1025 nm. These results demand changes of future breakdown modeling for water including the use of a larger band gap than previously employed, the introduction of an intermediate energy level for initiation, and consideration of the wavelength dependence of seed electron density.

H-type microchannel fiber humidity sensor by femtosecond laser-induced water breakdown

H-type microchannel in single-mode fiber was fabricated using femtosecond laser-induced water breakdown. The air can be brought into the fiber core position through H-type microchannel. As the relative humidity of the air changing from 25 to 60%, the transmission power of the fiber without coating any absorbent material on the fiber decreased more than −23 dB. The relative humidity sensitivity gets to as high as −1.00 dB/1%RH. The fiber with H-type microchannel structure can be used as humidity sensor as its high sensitivity, quick response, and low cost.

Optical fiber Fabry–Perot interferometer cavity fabricated by femtosecond laser-induced water breakdown for refractive index sensing

The Fabry-Perot interferometer (FPI) cavity in a single-mode fiber with two open faces was fabricated by using the method of femtosecond laser-induced water breakdown. Then the FPI cavity was annealed by the arc discharge to greatly smooth its internal surface. The whole fabrication process features simple operation and high efficiency. The fabricated FPI cavity exhibits a perfect interferometer spectrum with reflection loss of only -3 dB and fringe visibility of almost 30 dB. It can be used as a perfectly reliable liquid refractive index sensor, as it exhibits high sensitivity (1147.48 nm/RIU), good linearity (99.93%), good repeatability, high actual measurement accuracy (1.29×10(-4)RIU), large measurement range, and good temperature insensitive characteristic.

Exploring morphological variations of a laser-induced water jet in temporal evolution: formation of an air bubble enclosing a water drop

We explore the spatio-temporal dynamics of a water jet that is generated by laser-induced water breakdown beneath a flat free surface. We find that morphological variations in the temporal evolution can be divided into three categories depending on the depth parameter γ, which is the ratio of the water-breakdown depth to the maximum bubble radius. For a depth parameter in the range 0.8 ≤ γ ≤ 1.03, we observe an intriguing pattern formation in which an air bubble perfectly encloses a water drop through the process of the Plateau–Rayleigh instability.

Fabrication of a D-shaped fiber by femtosecond laser-induced water breakdown for carbon nanotubes’ evanescent field interaction mode-locking of a double-clad fiber laser

A D-shaped fiber was fabricated by femtosecond laser-induced water breakdown for a fiber laser mode-locked by the evanescent field interaction of carbon nanotubes. Then a mode-locked double-clad fiber laser was constructed using the D-shaped fiber with carbon nanotubes as a saturable absorber and an ytterbium-doped double-clad fiber pumped by a 915 nm fiber coupled multimode laser diode as an amplifying medium. Stable mode-locked operation at 1.07 μm was achieved with a full width at half maximum of 18.1 nm. The output pulses had a repetition rate of 5.76 MHz with a pulse duration of 136.2 fs. The energy per pulse was 52.5 nJ and the slope efficiency was about 11%.

Single microchannel high-temperature fiber sensor by femtosecond laser-induced water breakdown

Single microchannel high-temperature fiber sensors were fabricated by drilling a microchannel across the fiber core near the end of the common single-mode fiber using femtosecond laser-induced water breakdown. Then the microchannel was annealed by the arc discharge to smooth its inwall. The two sides of microchannel and the end surface of the fiber constitute three reflective mirrors, which form a three-wave Fabry-Pérot interferometer (FPI). The fabricated FPI can be used as a high-temperature sensor in harsh environments due to its large temperature range (up to 1000°C), high linearity, miniaturized size, and perfect mechanical property.

Exploration of water jet generated by Q-switched laser induced water breakdown with different depths beneath a flat free surface

The dynamics of a water jet on a flat free surface are investigated using a nanosecond pulsed laser for creating an oscillating bubble with different depths beneath the free surface. A thin jet is shown to deform a crater surface resulted from surface depression and cause a circular ring-shaped crater on the connection surface between the crater of surface depression and the thin jet. The collapse of this circular ring-shaped crater is proposed to the crown-like formation around a thick jet. The evolution of the bubble depth suggests a classification of four distinctive ranges of the bubble depths: non-crown formation when the parameter of bubble depth over the maximum bubble radius γ ≤ 0.5, unstable crown formation when 0.5 ≤ γ ≤ 0.6, crown-like structure with a complete crown wall when 0.6 ≤ γ ≤ 1.1, and non-crown formation when 1.1 ≤ γ. Furthermore, the orientation of the crown wall gradually turns counterclockwise to vertical direction with increasing γ from 0.5 to 1.1, implying a high correlation between the orientation of the crown wall and the depth of the bubble. This correlation is explained and discussed by the directional change of the jet eruption from the collapse of circular ring-shaped crater.

Liquid refractive index sensor with three-cascaded microchannels in single-mode fiber fabricated by femtosecond laser-induced water breakdown

Liquid refractive index sensor with three-cascaded microchannels in single-mode fiber was fabricated by femtosecond laser-induced water breakdown. When the liquid is filled in three microchannels across the fiber core, the transmission spectrum of the sensor shows interference peaks. The refractive index of liquid can be sensed accurately based on both the wavelength shift and loss change of interference peaks. The refractive index sensitivities of wavelength shift and loss change reach to as high as −2,406.1 nm/RIU and −156.8 dB/RIU, respectively. The sensor is insensitive to the refractive index change of liquid caused by environmental temperature. It can be used for liquid refractive index sensing with high sensitivity, especially for water pollution monitoring.

Etching of long fiber polymeric composite materials by nanosecond laser induced water breakdown plasma

Composite materials are widely used in industry due to their superior material properties and light weight. However, shear failure can occur at the interface between the fibers and polymer matrix when a tensile force stretches the matrix more than the fibers. Repairing the damaged composite material appears to be cost effective but still remains a challenge despite extensive research. Laser induced water breakdown plasma, which is generated by the strong interaction between nanosecond laser and water, is proposed in this work to etch the surface layer of a carbon fiber reinforced composite sample. It is found that the polymer layer can be effectively removed by the plasma while the carbon fiber remains almost intact. The dependence of the etching depth on the laser power density, laser focus position, and the number of shots are also investigated in this work. The maximum possible etching depth is around 350μm with 50 laser shots at laser power density of 70GW/cm2.