Repetition rates

Dadap J I, Hu X F, Russell N M, Ekerdt J G, Lowell J Kand Downer M C 1995 Analysis of second-harmonic generation by unamplified, high-repetition-rate, ultrashort laser pulses at Si(OOI) interfaces/ J. Selected Topics Quantum Electron 1 1145-55... 

The most connnon commercially prepared amplifier systems are pumped by frequency-doubled Nd-YAG or Nd-YLF lasers at a 1-5 kHz repetition rate a continuously pumped amplifier that operates typically in the 250 kHz regime has been described and implemented connnercially [40]. The average power of all of the connnonly used types of Ti-sapphire amplifier systems approaches 1 W, so the energy per pulse required for an experiment effectively detennines the repetition rate. 

Knox W H, Downer M C, Fork R L and Shank C V 1984 Amplified femtosecond optical pulses and continuum generation at 5 kHz repetition rate Qpt. Lett. 9 552-4... 

Rudd J V, Korn G, Kane S, Squier J, Mourou G and Bade P 1993 Chirped-pulse amplification of 55 fs pulses at a 1 kHz repetition rate in a TIAI203 regenerative amplifier Opt. Lett. 18 2044-6... 

Hz repetition rate of the lasers and is usually sampled with a gated integrator, whose output is reeorded with a laboratory eomputer. Analogue, rather than digital, eleetronies is usually employed beeause of pile-up of the deteeted photon eounts in an experiment with reasonable produet intensities. 

For the sake of illustration, a TOF analyzer could be likened to a camera taking snapshots of the m/z values of an assembly (beam) of ions the faster the repetition rate at which the camera shutter is clicked, the greater is the number of mass spectra that can be taken in a very short time. For TOF analyzers, it is not uncommon to measure several thousand mass spectra in one second All such spectra can be added to each other digitally, a process that improves the signal-to-noise ratio in the final accumulated total. 

In order to prevent this occurring a pulsed method of pumping is used with a repetition rate low enough to allow time for Tj — Sq relaxation. For CW operation either Tj must be sufflciently short or another dye has to be used for which T2 — Ti absorption does not overlap with the fluorescence. 

A pulsed dye laser may be pumped with a flashlamp surrounding the cell through which the dye is flowing. With this method of excitation pulses from the dye laser about 1 ps long and with an energy of the order of 100 mJ can be obtained. Repetition rates are typically low - up to about 30 FIz. 

In bofh CW and pulsed lasers fhe dye solution musf be kepf moving to prevenf overheating and decomposition. In a pulsed laser fhe dye is continuously flowed fhrough fhe confaining cell. Alternatively, magnetic stirring may be adequate for low repetition rates and relatively low power. In a CW laser fhe dye solution is usually in fhe form of a jef flowing rapidly across fhe laser cavify. 

This is in contrast to lasers based on mby or neodymium in glass, which operate at much lower pulse-repetition rates. Nd YAG lasers are often operated as frequency-doubled devices so that the output is at 532 nm. These lasers are the most common type of soHd-state laser and have dominated sohd-state laser technology since the early 1970s. Nd YAG lasers having continuous output power up to 1800 W are available, but output powers of a few tens of watts are much more common. 

A typical example might involve use of a krypton fluoride excimer laser operating at 249 nm with a pulse duration around 100 nanoseconds and a pulse repetition rate which can be varied up to 200 Hz. For metal deposition, energy densities in the range from 0.1 to 1 J/cm per pulse are typical. 

Heteronuclear chemical shift-correlated spectroscopy, commonly called H-X COSY or HETCOR has, as the name implies, different and F frequencies. The experiment uses polarization transfer from the nuclei to the C or X nuclei which increases the SNR. Additionally, the repetition rate can be set to 1—3 of the rather than the longer C. Using the standard C COSY, the ampHtude of the C signals are modulated by the... 

Atomic- Vapor Laser Isotope-Separation. Although the technology has been around since the 1970s, laser isotope separation has only recently matured to the point of industrialization. In particular, laser isotope separation for the production of fuel and moderators for nuclear power generation is on the threshold of pilot-plant demonstrations in several countries. In the atomic vapor laser isotope-separation (AVLIS) process, vibrationaHy cooled U metal atoms are selectively ionized by means of a high power (1—2 kW) tunable copper vapor or dye laser operated at high (kHz) repetition rates (51,59,60). 

MPI is especially valuable for elemental analyses with typical useful yield of 10 . Because SALI is laser-based, expected improvements over the next few years, in particular for vacuum-ultraviolet laser technology, should have a significant impact. High repetition rate Nd—YAG systems with sufficient pulse energy are already available to 50 Hz, and probably can be extended to a few hundred Hz. 

Company Model Maximum repetition rate [Hz] Pulse energy [mJ] ... 

A commercial fs-laser (CPA-10 Clark-MXR, MI, USA) was used for ablation. The parameters used for the laser output pulses were central wavelength 775 nm pulse energy -0.5 mj pulse duration 170-200 fs and repetition rate from single pulse operation up to 10 Hz. In these experiments the laser with Gaussian beam profile was used because of the lack of commercial beam homogenizers for femtosecond lasers. 

Frequency is the repetition rate of pressure variations, and it is described by the reciprocal of the period time T ... 

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