Nek M. Shaikh

Measurement of electron density and temperature of a laser-induced zinc plasma

We report spectroscopic studies of the zinc plasma produced in air by the three harmonics of a Q-switched pulsed Nd : YAG laser at 1064, 532 and 355 nm. The electron temperature has been determined from the intensity ratio of the transitions (4s4d 3 D3 → 4s4p 3 P2) at 334.5 nm and (4s5s 3 S1 → 4s4p 3 P2) at 481.0 nm of neutral zinc, whereas the electron number density has been evaluated from the Stark broadening of the (4s4d 3 D3 → 4s4p 3 P2) transition at 334.5 nm. It is observed that both these parameters decrease as the distance from the target surface increases and it increases with an increase in the laser irradiance. The power law is fitted to the experimental data.

Spectroscopic studies of Ca plasma generated by the fundamental, second, and third harmonics of a Nd:YAG laser

The ablation of calcium sample has been studied by the optical emission spectroscopy of the evolving plasma using the fundamental, second, and third harmonic of a Nd:YAG laser, which reveals numerous transitions due to neutral and singly ionized calcium. The measurements have been performed to determine the electron temperature and electron number density and their spatial behavior. In addition, the behavior of the electron temperature and number density as a function of laser irradiance and ambient gas pressure has been studied. The processes of laser photon absorption in the plasma through inverse bremsstrahlung and photoionization have also been discussed.

Diagnostics of cadmium plasma produced by laser ablation

Optical measurements of the cadmium plasma produced by the fundamental, second, and third harmonics of a Nd:YAG laser are reported. The excitation temperature and ionic temperature have been determined from the Boltzmann plot and Saha equation, whereas the number density is estimated from the Stark broadened profile of the spectral lines. The variations in the excitation temperature and number density with the ambient air pressure as well as with the laser irradiance have been studied. Besides, the spatial distributions of the temperature and number density have been investigated.

Laser wavelength effects on the charge state resolved ion energy distributions from laser-produced Sn plasma

The effects of laser wavelength on the charge state resolved ion energy distributions from laser-produced Sn plasma freely expanding into vacuum are investigated. Planar Sn targets are irradiated at laser wavelengths of 10.6 and 1.064 μm and intensities of 1.8×1010 and 3.4×1011 W/cm2, respectively. These parameters are relevant to the extreme ultraviolet x-ray source application. An electrostatic deflection probe and single channel electron multiplier are used to record the charge state resolved ion energy distributions 100 cm from the laser plasma source. At the longer laser wavelength, higher charge state ions are observed. At both laser wavelengths, the peak ion energies increase approximately linearly as a function of charge state, and all ion energies greatly exceed the initial thermal electron temperature. The differences in the ion energy distributions are attributed to the laser wavelength dependence of the laser energy absorption, the resulting plasma density in the corona, and the subsequent rec...

Spectroscopic characterization of laser ablation brass plasma

We present optical emission studies of the laser ablation brass plasma generated by the fundamental, second, and third harmonics of a neodymium doped yttrium aluminum garnet laser. The spectra predominantly reveal the spectral lines of the neutral and singly ionized copper and zinc. The excitation temperatures are determined by the Boltzmann plot method, whereas the electron number densities have been extracted from the Stark broadened line profiles. The spatial variations in the spectral line intensities and the plasma parameters at 1000, 500, and 100 mbar air pressures have been evaluated. Besides, the effect of the ambient gases (He, Ne, and Ar), the laser irradiance, and the laser wavelengths on the plasma parameters have been investigated.

Plasma properties of laser-ablated strontium target

Optical emission spectroscopy is used to characterize the laser-produced strontium plasma by using the fundamental, second, and third harmonics of a Nd:YAG laser. Variations in the electron temperature (Te) and number density (Ne) as a function of distance, laser irradiance, and ambient gas pressure have been studied by using the emission lines of neutral strontium. In addition, absorption mechanisms responsible for the variation of the electron temperature and number density and the dependence of the spectral line intensities on the ambient gas pressure and laser irradiance are discussed.

Optical emission studies of the mercury plasma generated by the fundamental, second and third harmonics of a Nd : YAG laser

We report the first measurements of the optical emission spectra of mercury plasma produced by the fundamental, second and third harmonics of a Nd : YAG laser, which reveals numerous transitions due to the neutral and singly ionized mercury. The excitation temperature has been determined from the Boltzmann plots, whereas the electron number density is estimated from the Stark broaden profile of the spectral lines. The estimated range of the excitation temperature and the electron number density is (7000–14000) K and (3.6 × 1016 to 2.5 × 1017) cm−3, respectively. The behaviour of the excitation temperature and the electron number density with the laser irradiance has been studied. The spatial distribution of the temperature and the electron number density has also been investigated besides the studies of absorption in the plasma through inverse bremstrahlung and photoionization.

Spectroscopic studies of tin plasma using laser induced breakdown spectroscopy

Laser-induced Sn plasma generated at different laser intensities has been characterized using visible emission spectroscopy. A CO2 laser pulse 85 ns in duration is used to generate plasma from a planar Sn sample in a vacuum of 10?5 torr. The plasma electron temperature is inferred by the Boltzmann plot method from singly ionized Sn emission lines, and plasma electron density is inferred using Stark broadened profiles. Electron temperature is measured in the range of (0.53 ? 1.28) eV, and electron density is measured in the range of (9.19?1015 ? 7.45?1016) cm?3, as the laser intensity is varied from (1?1010 to 2.5?1010) W/cm2. The plasma shielding effect has been observed within the laser intensities of (2?1010 ? 2.5?1010) W/cm2.

Interaction of a

The interaction of a CO2 laser pulse with Sn-based plasma for a 13.5-nm extreme ultraviolet (EUV) lithography source was investigated. It was noted that a CO2 laser with wavelength of 10.6 ¿m is more sensitive to surface impurities as compared with a Nd:YAG laser with wavelength of 1.06 ¿m . This reveals that a CO2 laser is more likely absorbed in a thinner layer near the target surface. Compared with a Nd:YAG laser, a CO2 laser shows higher in-band (2% bandwidth) conversion efficiency (CE) with a solid Sn target due to less reabsorption of the EUV emission induced by the plasma. However, with foam targets containing low concentrations of Sn, the in-band CE is lower than that with solid Sn. The CE can be enhanced with plasma confinement. These results suggest that a driving laser with wavelength between 1.06 and 10.6 ¿m may be an even better choice to generate higher CE from laser to 13.5-nm EUV emission.

\hbox{CO}_{2}

A CO(2) laser system with flexible parameters was developed for fundamental research related to an extreme ultraviolet (EUV) lithography source. The laser is a master oscillator and power amplifier (MOPA) system, consisting of a master oscillator, an externally triggered plasma switch, a preamplifier, a main amplifier, and electronic synchronization units. The laser pulse duration can be varied easily from 10 to 110 ns, with a constant peak power for pulse durations from 25 to 110 ns. The MOPA laser system can also be operated in dual-oscillator mode to produce laser pulse with pulse duration as long as 200 ns and a train of laser pulses with flexible interval. The divergence of the laser beam is 1.3 times the diffraction limit. The laser intensity on the target surface can be up to 8x10(10) W/cm(2). Utilizing this CO(2) MOPA laser system, high conversion efficiency from laser to in-band (2% bandwidth) 13.5 nm EUV emission has been demonstrated over a wide range of laser pulse durations.