An official website of the United States government
Counter-propagating ultrafast pulses can disrupt the phase of harmonic generation, and offer a means to achieve quasi-phase matching in processes like high-order harmonic generation. Optimizing this process requires accurate modeling. Using second harmonic generation (SHG) as a simpler and more accessible proxy, we compare the results of two numerical simulations to experimental measurements of SHG with counter-propagating pulses. The first follows previous theoretical work in assuming a quasi-CW pulse and solving the nonlinear wave equation in the time-domain. However, we find that adapting a frequency-domain model to account for the broadband nature of ultrafast pulses better reproduces the salient features we observe in our experimental results.
more »
« less
Pulse Measurement of Second-Harmonic Generation from Random Quasi-Phase-Matching in ZnS
We use 2.4-micron laser pulses to produce second-harmonic generation via random quasi-phase-matching in ZnS. Using a frequency-resolved optical gating system, we reconstruct the complex temporal profile of the second-harmonic pulses.
more »
« less
- Award ID(s):
- 2048263
- PAR ID:
- 10580047
- Publisher / Repository:
- Optica Publishing Group
- Date Published:
- ISSN:
- 2160-8989
- ISBN:
- 978-1-957171-39-5
- Page Range / eLocation ID:
- JW2A.44
- Format(s):
- Medium: X
- Location:
- Charlotte, North Carolina
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Generating wavelength-tunable picosecond laser pulses from an ultrafast laser source is essential for femtosecond stimulated Raman scattering (FSRS) measurements. Etalon filters produce narrowband (picosecond) pulses with an asymmetric temporal profile that is ideal for stimulated resonance Raman excitation. However, direct spectral filtering of femtosecond laser pulses is typically limited to the laser’s fundamental and harmonic frequencies due to very low transmission of broad bandwidth pulses through an etalon. Here, we show that a single etalon filter (15 cm−1 bandwidth; 172 cm−1 free spectral range) provides an efficient and tunable option for generating Raman pump pulses over a wide range of wavelengths when used in combination with an optical parametric amplifier and a second harmonic generation (SHG) crystal that has an appropriate phase-matching bandwidth for partial spectral compression before the etalon. Tuning the SHG wavelength to match individual transmission lines of the etalon filter gives asymmetric picosecond pump pulses over a range of 460–650 nm. Importantly, the SHG crystal length determines the temporal rise time of the filtered pulse, which is an important property for reducing background and increasing Raman signals compared with symmetric pulses having the same total energy. We examine the wavelength-dependent trade-off between spectral narrowing via SHG and the asymmetric pulse shape after transmission through the etalon. This approach provides a relatively simple and efficient method to generate tunable pump pulses with the optimum temporal profile for resonance-enhanced FSRS measurements across the visible region of the spectrum.more » « less
-
Attosecond pulses formed by high order harmonics (HHs) of an infrared (IR) laser field is a powerful tool for studying and controlling ultrafast dynamics of electrons in atoms, molecules and solids at its intrinsic time-scale. However, in the X-ray range the energy of attosecond pulses is rather limited. Their amplification is an important but very challenging problem since none of the existing amplifiers can support the corresponding PHz bandwidth. In our previous work [1] we proposed a method for the attosecond pulse amplification in hydrogen-like active medium of a recombination plasma-based X-ray laser dressed by a replica of the fundamental frequency IR field used for the HH generation. Due to the IRfield-induced sub-laser-cycle Stark shift and splitting of the lasing energy levels the gain of the active medium is redistributed over the combination frequencies, separated from the resonance by even multiples of the frequency of the IR field. If the incident HHs forming an attosecond pulse train are tuned in resonance with the induced gain lines and the active plasma medium is strongly dispersive for the modulating IR field, then during the amplification the relative phases of harmonics and (under the optimal choice of the IR field strength) the shape of the amplified pulses will be preserved. In the present work we show the possibility of boosting the efficiency of HH amplification by modulating the active medium of an X-ray laser with the second harmonic of the fundamental frequency IR field. We show that under the action of a laser field (with arbitrary frequency) the gain redistribution occurs not only over the even combination frequencies discussed in [1], but also over the odd frequencies separated from the resonance by odd multiples of the laser frequency. Besides, nearly half of the medium gain is contained in the even induced gain lines, and nearly half in the odd. If the modulating field is the second harmonic of the IR field, used for the generation the HHs and attosecond pulses, then the seeding HHs can be tuned in resonance with both even and odd gain lines simultaneously, which will make the overall gain much higher as compared to the previously considered case of the fundamental frequency modulating field (when only the even gain lines play the role). By the example of the C5+ X-ray laser with 3.38 nm wavelength of the inverted transition we show the possibility of increasing the efficiency of 430 as pulse amplification by 8.5 times when the active medium is modulated with the second harmonic of the fundamental frequency IR field with wavelength 2.1 µm.more » « less
-
David L. Andrews; Enrique J. Galvez; Halina Rubinsztein-Dunlop (Ed.)We review highlights of our recent contributions to understanding the propagation dynamics and transverse orbital angular momentum of optical pulses carrying spatiotemporal optical vortices (STOVs). STOVs, which were first observed as an emergent phenomenon in nonlinear self-focusing, were first linearly generated using a 4𝑓 pulse shaper and measured using transient-grating single-shot supercontinuum spectral interferometry (TG-SSSI). That STOV-based transverse orbital angular momentum (OAM) is carried at the single photon level was then confirmed in measurements of OAM conservation in second harmonic generation. Our recent theory for the electromagnetic mode structure and transverse OAM of STOVcarrying pulses in dispersive media predicts half-integer OAM and the existence of a transverse OAM-carrying quasiparticle: the bulk medium STOV polariton.more » « less
-
Sub-picosecond timing jitter between optically synchronized femtosecond and picosecond laser systemsAbstract Synchronized optical pulses are widely used. We report here characterization and measurement of synchronized femtosecond and picosecond pulses from a Ti:Sapphire laser (nominally 800 nm) and a Nd:YAG laser (1064 nm), respectively. Synchronization is achieved by utilizing soliton self-frequency shift in a photonic-crystal fiber that allows the 800 nm femtosecond oscillator to seed the third-harmonic generation (355 nm) of picosecond regenerative amplifier. The relative timing jitter between the amplified femtosecond and the third-harmonic generation of picosecond pulses is (710 ± 160) fs, which is only (1.17 ± 0.26)% of the picosecond pulse duration. This work paves way for applications in stimulated Raman scattering spectroscopy and amplification.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1364/CLEO_AT.2024.JW2A.44
