The phase stability of broadband (280 nm bandwidth) terawatt-class parametric amplification was measured, for the first time to our knowledge, with a combination of spatial and spectral interferometry. Measurements at four different wavelengths from 750 to 900 nm were performed in combination with numerical modeling. The phase stability is better than 1/23 rms of an optical cycle for all the measured wavelengths, depending on the phase-matching conditions in the amplifier. © 2007 Optical Society of America OCIS codes: 190.4970, 320.7090, 320.7160, 350.5030. The generation and amplification of phase-controlled few-cycle laser pulses is a necessity for applications such as quantum interference metrology [1], attosecond science [2], and quantum control of, e.g., molecular dynamics [3]. Intense, phase-stable few-cycle laser pulses have been produced by using Ti:sapphire amplifiers and subsequent spectral broadening in filaments. However, filamentation in gas-filled hollow fibers [4], or directly in a gas cell [5], is difficult to scale beyond Ϸ0.2 TW. In parametric amplification phase-stable pulses, albeit at moderate energies of a few hundred microjoules [6][7][8][9], have also been demonstrated. The generation of multimillijoule-level phase-controlled few-cycle pulses with terawatt (TW) intensity has not been demonstrated to date. In this Letter we report what is, to the best of our knowledge, the first measurement of the phase stability of TW-class ultrafast amplification. The amplifier is based on noncollinear optical parametric chirped pulse amplification (NOPCPA) and was described elsewhere in detail [10]. It consists of a double-pass preamplifier and a single-pass power amplifier using BBO crystals. The seed laser is a home-built 6.2 fs frequency comb oscillator, producing phase-locked 5.5 nJ pulses at a 75 MHz repetition rate. The carrier-envelope phase (CEP) stability of the oscillator is 1 / 46 rms of an optical cycle. The 532 nm pump laser provides 170 mJ pulses with a duration of 60 ps and is synchronized to the oscillator laser. The system operates at a repetition rate of 30 Hz and is capable of generating 7.6 fs pulses at 2 TW (15.5 mJ after compression) when the normal full seed energy of 1 nJ per pulse is available.The phase stability of the NOPCPA output is measured with linear interferometry. The advantage of this method over the frequently used f :2f technique [11] is that pulse intensity fluctuations (typically a few percent) do not influence the measurement; also the wavelength dependence can be measured. The system is based on a double interferometer, to be able to correct for optical path fluctuations due to external noise and drift (see Fig. 1). The interferometer path length variations, of the order of a wavelength, are too small to influence the CEP. Changes induced by thermal effects due to the 20 mm of optical material in the NOPCPA path are small and are in addition compensated by a similar amount of material in the reference arm. The interferometer compares interference [12] between...
Abstract:We demonstrate phase stable, mJ-level parametric amplification of pulse pairs originating from a Ti:Sapphire frequency comb laser. The amplifier-induced phase shift between the pulses has been determined interferometrically with an accuracy of ≈ 10 mrad. Typical phase shifts are on the order of 50-200 mrad, depending on the operating conditions. The measured phase-relation can be as stable as 20 mrad rms (1/300 th of an optical cycle). This makes the system suitable for Ramsey spectroscopy at short wavelengths by employing harmonic upconversion of the doublepulses in nonlinear media.
Passive mode-locking in two-section InAs/InP quantum dot laser diodes operating at wavelengths around 1.55 µm is reported. For a 4.6-GHz laser, a large operating regime of stable mode-locking, with RF-peak heights of over 40 dB, is found for injection currents of 750 mA up to 1.0 A and for values of the absorber bias voltage of 0 V down to −3 V. Optical output spectra are broad, with a bandwidth of 6-7 nm. However, power exchange between different spectral components of the laser output leads to a relatively large phase jitter, resulting in a total timing jitter of around 35 ps. In a 4-mm-long, 10.5-GHz laser, it is shown that the operating regime of stable mode-locking is limited by the appearance of quantum dot excited state lasing, since higher injection current densities are necessary for these shorter lasers. The output pulses are stretched in time and heavily up-chirped with a value of 16-20 ps/nm. This mode of operation can be compared to Fourier domain mode-locking. The lasers have been realized using a fabrication technology that is compatible with further photonic integration. This makes such lasers promising candidates for, e.g., a coherent multiwavelength source in a complex photonic chip.
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