Carrier-envelope offset frequency stabilization of a thin-disk laser oscillator operating in the strongly self-phase modulation broadened regime

Abstract

We demonstrate the carrier-envelope offset (CEO) frequency stabilization of a Kerr lens mode-locked Yb:Lu 2 O 3 thin-disk laser oscillator operating in the strongly self-phase modulation (SPM) broadened regime. This novel approach allows overcoming the intrinsic gain bandwidth limit and is suited to support frequency combs from sub-100-fs pulse trains with very high output power. In this work, strong intra-oscillator SPM in the Kerr medium enables the optical spectrum of the oscillating pulse to exceed the bandwidth of the gain material Yb:Lu 2 O 3 by a factor of two. This results in the direct generation of 50-fs pulses without the need for external pulse compression. The oscillator delivers an average power of 4.4 W at a repetition rate of 61 MHz. We investigated the cavity dynamics in this regime by characterizing the transfer function of the laser output power for pump power modulation, both in continuous-wave and mode-locked operations. The cavity dynamics in mode-locked operation limit the CEO modulation bandwidth to ~10 kHz. This value is sufficient to achieve a tight phase-lock of the CEO beat via active feedback to the pump current and yields a residual in-loop integrated CEO phase noise of 197 mrad integrated from 1 Hz to 1 MHz.

Carrier-Envelope Offset Frequency Stabilization of a Thin-Disk Laser Oscillator via Depletion Modulation

“…The resulting error signal is amplified in a proportional-integral servo controller (MenloSystems PIC201) and the feedback signal is applied either to a voltage-to-current (V-I) converter to modulate the current of the pump diode, to the AOM modulating the power of the 3 W beam shining onto the disk, or to both simultaneously. The home-designed V-I converter (same one as used in [13], with an electrical modulation bandwidth of 1 MHz) is connected to the wavelength-stabilized 969 nm pump diode in parallel to a high DC power supply unit (PSU). A 7 Hz low-pass filter prevents cross-talk between the V-I converter and PSU [13].…”

“…The home-designed V-I converter (same one as used in [13], with an electrical modulation bandwidth of 1 MHz) is connected to the wavelength-stabilized 969 nm pump diode in parallel to a high DC power supply unit (PSU). A 7 Hz low-pass filter prevents cross-talk between the V-I converter and PSU [13]. The coarse control of f CEO is done via a pair of fused silica wedges, inserted at Brewester's angle into the laser cavity [20].…”

“…After f CEO detection, stabilization of this parameter in TDLs has been mainly done via modulation of the pump power. This was realized either by using a dedicated electronic module (voltage-to-current converter) placed in parallel to the high current DC source for direct modulation of the pump diode [11]- [13], or by the dichroic combination of a second low-power pump diode with fast modulation capabilities to avoid the modulation of high currents at high frequencies [15]. However, the former requires electronics which are not commercially available and the latter, besides using an in-house coated dichroic mirror, manipulates the pump beam path, which might be detrimental at high pump powers.…”

XUV Sources Based on Intra-Oscillator High Harmonic Generation With Thin-Disk Lasers: Current Status and Prospects

“…As discussed in Section III, operation with sub-150-fs is desirable for intra-oscillator HHG and a promising approach is to operate the TDL oscillator in the strongly SPM-broadened regime. So far, there has been only one study of f CEO stabilization in this regime [155]. The intracavity peak power was already 47 MW and owing to the 50-fs pulse duration, only 63 mW of output power were used for direct SCG, without the need for a nonlinear pulse compression stage [155].…”

“…So far, there has been only one study of f CEO stabilization in this regime [155]. The intracavity peak power was already 47 MW and owing to the 50-fs pulse duration, only 63 mW of output power were used for direct SCG, without the need for a nonlinear pulse compression stage [155]. Applying the peak power scaling procedure mentioned in Section III to this TDL oscillator operating in this regime should allow for a powerful driving source for intra-oscillator HHG, which makes this result very promising.…”