![\"\"](\"https:\/\/testwebc3.com.es\/wp-content\/uploads\/2020\/03\/CPA_scheme.png\")
<\/figure><\/div>\n\n\n\nFigure 1: Schematic overview of a chirped pulse amplifier laser system.<\/em><\/p>\n\n\n\n \n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nThe CPA laser system is comprised of four main sub-systems. The first\none consists of an oscillator that generates low energy femtosecond pulses at a\nbase rep rate of several MHz. A pulse picker selects 1 out of 106<\/sup> of\nall generated pulses to be injected into a stretcher, which uses a diffracting\ngrating with 1200 grooves per mm and is designed in an on-axis Oeffner configuration. After the stretcher\nthe amplification chain begins, consisting of three stages, one regenerative\nand two multi-pass amplifiers (Figure 1). All of them are pumped by diode\npumped frequency converted solid state laser. Once the pulse has reached proper\nenergy, a compressor using identical diffraction gratings as in the stretcher\nreverse the pulse length to its original temporal state, giving rise to a TW\npeak power. To avoid air-breakdown, the compressor is placed in a vacuum\nchamber with a Treacy design. The pulse is then finally focused into the target\nfor proton\/ion generation (Figure 2).\n\n\n\n<\/p>\n\n\n\n Figure 2: Schematic overview of a dual output MOPA pump laser setup used to pump the last amplifier stage in the CPA. <\/em><\/p>\n\n\n\n Figure 3: A strong and ultra-short laser pulse is directed onto a thin target and the generated particles inside the plasma are accelerated by means of its high electric field. Caused by the mass difference between electron and protons (m<\/em>p<\/em><\/sub>\/m<\/em>e<\/em><\/sub>\u2248 2000) both particle species are well separated after a short distance in vacuum.<\/em><\/p>\n\n\n\n The\npower densities achieved are so high (>1018<\/sup> W\/cm2<\/sup>)\nthat the laser basically acts as a particle accelerator when it reaches the\ntarget surface. After striking, electrons are directly accelerated and\npenetrate the target. Most of them spread and dissipate energy inside of it,\nbut the most energetic ones escape, leaving behind an electrostatic potential\nwhich generates an electric field that ionizes and accelerates surface ions in\na process called Target Normal Sheath Acceleration (TNSA).<\/p>\n\n\n\n As\na consequence, an intense collimated beam of high-energy protons is emitted\nnormal to the rear surface of the irradiated targets. This beam presents a\nspectrum of energies, typically with an exponential profile, and present three\nmain features (see Figure 4): a large energy spread, a smooth decrease of\nparticle number with energy and, finally, an abrupt \u201ccutoff\u201d that delimits the\nmaximum proton energy achievable and determines the experimental scaling laws\nfor the acceleration process. This spectrum is highly dependent on the target\nproperties, especially considering their thickness. After different\nexperiments, it has been proved that the maximum proton energy accelerated via\nTNSA can be enhanced by using thinner targets.<\/p>\n\n\n\n Despite\nthe promising results, proton accelerated energies are still low to be applied\nin cancer treatments. Nonetheless, the advantages over existing techniques like\ncyclotron accelerators (reduced radiation shielding requirements, compactness, energy\nconsumption or economic viability from institutions with constrained means) makes\nfurther developments to be worth the effort. That is why advances are being\nmade to increase the laser peak power up to the sub-petawatt level, all relying\non Monocrom current and improved pumping modules.<\/p>\n\n\n\n Figure 4: The graph visualizes the particle yield per narrow solid angle over particle energy for different target thicknesses. The maximum particle energy reached is clearly depended on the target thickness used. Spectral distribution is measured by a time of flight detector.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" 1 The Laser system In Monocrom we have tackled the challenges of generating high power ultra-short laser pulses by building a CPA laser system that is pumped by several MOPA systems. We used titanium doped sapphire (Ti:Sa) as the active material for both the oscillation…<\/p>\n","protected":false},"author":6,"featured_media":19421,"comment_status":"open","ping_status":"open","sticky":true,"template":"","format":"standard","meta":{"footnotes":""},"categories":[79,86],"tags":[],"_links":{"self":[{"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/posts\/19405"}],"collection":[{"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/comments?post=19405"}],"version-history":[{"count":11,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/posts\/19405\/revisions"}],"predecessor-version":[{"id":19791,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/posts\/19405\/revisions\/19791"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/media\/19421"}],"wp:attachment":[{"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/media?parent=19405"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/categories?post=19405"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/testwebc3.com.es\/en\/wp-json\/wp\/v2\/tags?post=19405"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/testwebc3.com.es\/wp-content\/uploads\/2020\/03\/Pumping-scheme.jpg\")
<\/figure><\/div>\n\n\n\n![\"\"](\"https:\/\/testwebc3.com.es\/wp-content\/uploads\/2020\/03\/Proton_generation_target_chamber_scheme.png\")
<\/figure><\/div>\n\n\n\n2 Proton\/ion generation<\/h4>\n\n\n\n
![\"\"](\"https:\/\/testwebc3.com.es\/wp-content\/uploads\/2020\/03\/Proton_energy_distribution.png\")
<\/figure><\/div>\n\n\n\n