36 research outputs found
Direct Frequency-Mode-Stable Laser Amplification at Terahertz Burst Rates
Generation of high-fidelity amplified pulse bursts with a regular interpulse
interval yields, in the spectral domain, an equidistant pattern of narrowband
spectral modes, similar to frequency combs produced by cw mode-locked lasers,
but with greatly increased pulse energy. Despite their great potential for
nonlinear spectroscopy, material processing, etc., such long frequency-stable
bursts are difficult to generate and amplify because of prominent temporal
intensity modulation even after strong dispersive pulse stretching. This study
presents a burst generation method based on a master-oscillator
regenerative-amplifier system that allows for chirped-pulse amplification (CPA)
with high scalability in pulse number. A gradual smoothing of temporal
intensity profiles at an increasing number of pulses is discovered,
demonstrating an unexpected recovery of the CPA performance at terahertz (THz)
intraburst repetition rates. In consequence, a self-referenced stable burst
spectral peak structure with megahertz (MHz) peak width is generated, without
risk of amplifier damage caused by interference of chirped pulses. This result
eliminates limitations in burst amplification and paves the way for
advancements in ultrashort-pulse burst technology, particularly for its use in
nonlinear optical applications.Comment: 21 pages, 12 figure
Highly efficient THz generation by optical rectification of mid-IR pulses in DAST
We report on efficient THz generation in DAST by optical rectification of intense mid-IR pulses centered at (i) 3.9 μm and (ii) its second harmonic at 1.95 μm. Suppression of multi-photon absorption shifts the onset of saturation of the THz conversion efficiency to pump energy densities, which are almost an order of magnitude higher as compared to conventional pump schemes at 1.5 μm. Despite strong linear absorption at 3.9 μm, DAST exhibits a high optical-to-THz conversion efficiency, which we attribute to resonantly enhanced nonlinearity and advantageous phase matching of the THz phase velocity and group velocity of the driving pulse. At 1.95 μm, we find that low linear and multi-photon absorption in combination with cascaded optical rectification lead to record optical-to-THz conversion efficiencies approaching 6%. The observed high sensitivity of the THz generation to the parameters of the mid-IR driving pulses motivates an in-depth study of the underlying interplay of nonlinear wavelength- and intensity-dependent effects
Rapid-scan nonlinear time-resolved spectroscopy over arbitrary delay intervals
Femtosecond dual-comb lasers have revolutionized linear Fourier-domain
spectroscopy by offering a rapid motion-free, precise and accurate measurement
mode with easy registration of the combs beat note in the RF domain. Extensions
of this technique found already application for nonlinear time-resolved
spectroscopy within the energy limit available from sources operating at the
full oscillator repetition rate. Here, we present a technique based on time
filtering of femtosecond frequency combs by pulse gating in a laser amplifier.
This gives the required boost to the pulse energy and provides the flexibility
to engineer pairs of arbitrarily delayed wavelength-tunable pulses for
pump-probe techniques. Using a dual-channel millijoule amplifier, we
demonstrate programmable generation of both extremely short, fs, and extremely
long (>ns) interpulse delays. A predetermined arbitrarily chosen interpulse
delay can be directly realized in each successive amplifier shot, eliminating
the massive waiting time required to alter the delay setting by means of an
optomechanical line or an asynchronous scan of two free-running oscillators. We
confirm the versatility of this delay generation method by measuring chi^(2)
cross-correlation and chi^(3) multicomponent population recovery kinetics
Rapid amplitude-phase reconstruction of femtosecond pulses from intensity autocorrelation and spectrum
The retrieval of time-dependent intensity and phase of femtosecond laser pulses is a long standing problem. To date, frequency-resolved optical gating (FROG) is probably the most trustworthy pulse measurement method. However, it requires a substantial experimental and numerical involvement. This motivates the quest for other simpler high-fidelity pulse measuring techniques. We present a new method of deciphering the pulse structure from the intensity autocorrelation trace and the intensity spectrum. We show that such a set of data is sufficient to restore the intensity and phase of a femtosecond pulse except for the typical uncertainties concerning the time shift and direction. The main feature of the proposed method is its robustness and swift convergence. Unlike a two-step pulse reconstruction, our algorithm employs the time- and frequency-domain data simultaneously, which in general provides a much faster convergence