Laser-induced optical breakdown applied for laser spark ignition

Abstract

In the present article, the experimental investigation of optical breakdown induced by ns/mJ pulses at two wavelengths, 1064 nm and 532 nm, in air of atmospheric pressure is reported and discussed. The obtained breakdown thresholds were compared with theory and are in good agreement. The generated plasmas have been characterized by their amount of scattered laser light, energy transmission, and change of the transmitted temporal shape. Laser-induced plasma formation in a gas, in air, also generates an acoustic pressure wave. The acoustic energy is compared to the laser pulse energy and is found to be linearly dependent. Moreover, the frequency distribution of the characteristic acoustic pressure wave was analyzed. The experiments described were accomplished in order to optimize a laser ignition system with regard to efficiency and costs. The laser system employed for these investigations is a compact high peak power, passively Q-switched, longitudinally diode-pumped solid-state laser. Such a "laser spark plug" should replace conventional spark plugs in internal combustion engines because conventional ignition has reached its limits in terms of efficiency and durability. Thereby, a reduction of pollutant emission should also be feasible.

Dynamics of laser induced micro-shock waves and hot core plasma in quiescent air

“…The same is clear from the shadowgraphs ( Fig. 3a-3f) corroborating with higher deposition of laser energy before the geometrical focus of the focusing optics (Monot et al, 1992;Schwarz et al, 2010) and with the observed on-axis self-emission intensity profiles (Fig. 3i).…”

“…Laser-plasma induced shockwaves in air threshold the low dense plasma created around the focal plane interacts with the laser pulse leading to deposition of energy at different positions along the propagation direction analogous to self-focusing, a phenomenon well-known for high-power laser beams propagating in air (Shen, 1984;Monot et al, 1992;Schwarz et al, 2010). Figure 4 shows R SW as a function of delay from the laser pulse for 50, 75, and 150 mJ laser energies.…”

“…Shockwaves (SWs) generated from laser induced optical breakdown of materials have found many applications like laser spark ignition for fuel-air mixtures, internal combustion engines, pulse detonations engines etc. (Schwarz et al, 2010), laser shock peening (Ding & Ye, 2006) as it is used to treat many aerospace products such as turbine blades and rotor components, discs, gear shafts and bearing components, surface cleaning (Luk'yanchuk, 2002), laser propulsion (Phipps et al, 2000;Wang et al, 2010), spectroscopic applications like laser induced breakdown spectroscopy (LIBS) (Miziolek et al, 2006;Kumar et al, 2011), understanding the formation of atmospheric oxides in the natural lightening (Hill et al, 1980;Sobral et al, 2000), gas dynamic flow (Jeong et al, 1998), ablation of surfaces (Kudryashov et al, 2011;Bigoni et al, 2010), spray and micro-jet formation from liquid droplets (Thoroddsen et al, 2009) to name a few. Biological applications involve SW lithotripsy used for the treatment of kidney stones (Kawahara et al, 1991) and gall bladder diseases, treatment of pancreatic and salivary stones and also in orthopedics (Delius et al, 1994).…”

Laser-induced reactive microplasma for etching of fused silica

“…Additionally, in the case of APPJ processing, the nozzle can be corroded by the plasma, requiring regular maintenance. Besides plasma ignition by electrical energy like RF or microwave power, plasma can also be generated in gas by laser radiation due to optical break down [14][15][16]. An optical breakdown can be achieved by focusing a laser beam in a gas when a critical power density is exceeded.…”

Characterization of energy transfer for passively Q-switched laser ignition

“…Most studies concerning the energy transfer and the plasma breakdown have been carried out with actively Q-switched nanosecond Nd:YAG lasers at fundamental or frequency-doubled wavelength. Schwarz et al [9] show that 532 nm radiation is advantageous for generating a plasma breakdown because of tighter focus area, whereas 1064 nm radiation is advantageous for transferring more energy to the plasma due to a greater plasma absorption efficiency. Moreover, investigations show that increasing focal length leads to raised minimum energy for ignition (MIE) and lower power density [10,11].…”