Investigation and suppression of pre-pulses on nanosecond time scale in the SULF-1PW laser

Abstract

It is of crucial significance to investigate and suppress pre-pulses on nanosecond time scale because the intense pre-plasma generated by them may have enough time to expand and, thus, cause fatal impact on laser-matter interactions. In this research, we analyze the potential origins of pre-pulses on nanosecond time scale in a typical Ti:sapphire chirped pulse amplification laser system. Based on the analysis, the initial status of these generated pre-pulses in the SULF-1PW laser is measured and investigated. Then different measures, including fine control on the time synchronization and the replacement for the Ti:sapphire, are adopted in the SULF-1PW laser to suppress these pre-pulses with respective origins, which can promote the energy ratio between the main pulse and these pre-pulses by 2–3 orders of magnitude. This research not only improves the temporal contrast of the SULF-1PW laser on nanosecond time scale but also provides beneficial guidance for the design and construction of similar laser facilities.

Suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser

“…1(b). The time interval t p between the main pulse and the third type of ns prepulse (R3) corresponds to the distance l pm between PC1 and M2 [21] . To suppress the prepulse R3 by the pulse pickers more effectively, the time interval t p should be larger than the leading edge of the picking gate.…”

“…It should be noticed that the −4 ns prepulse still overlaps with the ASE pedestal [15] . Before the RA is optimized, the prepulse would easily be covered by the ASE pedestal [21] . With a fine adjustment on the switching-on time of PC2/PC3, the 4 ns pre-pulse would decay to an undetectable level, as shown in Fig.…”

“…In a typical CPA laser system, the ns prepulses mainly originate from a regenerative amplifier (RA), a multipass amplifier, and a four-grating compressor [21] . The ns prepulse generated from the four-grating compressor can be suppressed by blocking the zeroth-order diffraction of the gratings.…”

“…As analyzed in Ref. [21], the ns prepulses generated from RA mainly include three types: R1, the leaked ns prepulses due to the limited extinction ratio of the thin-film polarizer (TFP); R2, the ns prepulses from the mismatch on cavity length between the oscillator and the following RA; and R3, the ns prepulse arising from the Pockels cell (PC) in the RA. The first type of ns prepulse can be suppressed by adding pulse pickers after the RA, while the second type of ns prepulse can be suppressed by adding pulse pickers before the RA.…”

“…As mentioned in Ref. [21], the ns prepulses were measured mainly by employing a photodiode (ET2030, Electro-Optics Technology) and an oscilloscope (MSO58, Tektronix).…”