Stable generation of high-power subnanosecond laser pulses
S. Gagarsky, P. Gnatyuk , M. Inochkin, K. Fedin, L. Khloponin, V. Khramov Laser Technologies and Bio-Medicine Optics
NRU ITMO Saint-Petersburg, Russia
Abstract — A compact Nd:YAG laser with pulse energy more than 700mJ at 1064nm wavelength with individual spike duration less than 0.8ns was build. Supershort-term quasiperiodic Q-modulation of laser cavity was used for generation of stable subnanosecond pulses.
Keywords — pulsed solid-state laser; Q-switching; stable subnanosecond pulses.
The possibility of generating of high-power subnanosecond pulses in solid-state lasers with electro-optic Q-switching is well known [1-2]. In these works so called short-term modulation of the laser cavity losses during a number of axial periods was used. The most stable subnanosecond generation was achieved by means of delayed electro-optical negative feedback which allowed to automatically coordinate modulation period and axial period (double-pass time) of laser resonator [3]. However, the complexity and bulkiness of such systems prevents to their widespread practical application in compact laser systems. The same disadvantages are intrinsic for other methods of powerful subnanosecond pulses generation based on multipass amplification of radiation of subnansecond microchip laser or compression of nanosecond pulses in nonlinear optical media (require extra space and additional bulky and expensive optical elements like optical isolators, nonlinear cells, etc.).
In this work we developed and investigated a compact subnanosecond Nd:YAG laser with sub-joule level of output energy. The laser is based on previously developed compact nanosecond laser master oscillator power amplifier (MOPA) system with unstable oscillator cavity [4]. In present work we used a supershort-term quasiperiodic Q-modulation of master oscillator cavity without any feedback components. It was shown that application of specially generated voltage pulse with maximum amplitude of 10-20% greater than half-wave voltage to Pockels cell gives possibility to obtain stable trains of subnanosecond pulses with high energy.
Figure 1 shows experimental data: Pockels cell transmission dynamics (upper line 1) and oscilloscope traces of laser pulses (line 2 below). Pockels cell transmission was investigated for radiation of auxiliary Nd:YAG CW-laser.
During design time repetition quasiperiods of shutter transmission peaks and valleys were adjusted to be approximately equal to axial period of laser resonator. Line 2 shows about 200 superimposed oscillograms of the output laser shots. For visualization purposes transmission curve (line 1) at
Fig.1 is shifted in time by the value of laser generation build-up time to superpose with the output laser pulses. The total energy of compact MOPA system where both active rods were located in one laser head is more than 0.7J. Width of individual spike of generation is less than 0.8ns and pulse repetition rate is 10 Hz. It is worth to note that dimensions of the laser module allow to embed it in a handpiece disposed for example in the operator's hand.
Fig. 1. Experimental oscilloscope traces for transmission of electro-optic shutter (upper curve) and laser pulses (superimposed for 200 laser shots), oscilloscope was triggered by electrical pulse of Pockels cell driver.
References
[1] V. Anikeev, V. N. Khramov, K. A. Levin, "Neodymium lasers with short-term periodic loss modulation", QUANTUM ELECTRON, 1996, 26(1), 57-59.
[2] V. Anikeev, R. Sh. Zatrudina, "Negative feedback in an actively mode- locked laser", QUANTUM ELECTRON, 1995, 25 (1), 42-44.
[3] M. Inochkin, A. Pavlishin, “Mode-locking solid-state lasers with a delayed negative feedback”, Scientific And Technical Journal Of Information Technologies, Mechanics And Optics, 2001, 4(4), 47-54.
[4] M. Inochkin, V. Nazarov, K. Fedin, L. Khloponin, V. Khramov "High- powered compact Nd:YAG laser with unstable resonator", Scientific and Technical Journal «Priborostroenie», 2013, 56(9), 7-11.
