Spectrally compensated sum-frequency mixing scheme for generation of broadband radiation at 193 nm

Abstract

A dispersively compensated scheme for sum-frequency mixing of broadband ultrashort laser pulses is reported. An increase of the bandwidth of the sum-frequency mixing process by 12 times compared with the noncompensated bandwidth of the given crystal has been demonstrated. Mixing radiation at 266 and 707 nm in a 1-mm-thick beta-barium metaborate crystal by using the compensated scheme results in an output bandwidth of 0.6 nm at 193 nm, which corresponds to a minimum output pulse duration of 90 fs.The interest in various applications of far-UV and VIJV laser pulses, such as ultrafast photodissociation studies of molecules or laser-induced fluorescence spectroscopy, has led to the development of methods to generate intense, coherent light in this part of the spectrum. A particularly important wavelength in this range is 193 nm, which is the wavelength of the ArF excimer laser. Ultrashort seed pulses at 193 nm can be amplified to gigawatt power levels. [1][2][3] Frequency tripling of the ArF laser has been reported to be a useful source of 64-nm radiation, 4 which can find important applications in biology and lithography. Short-pulse high-brightness ArF laser systems can be considered as a promising pump source for the production of x rays and laboratoryscale x-ray laser schemes, 5 but they may also play a fundamental role in extending the range of the ultrafast photodynamical studies of molecules' into the VU1V region.Different methods of generating 193-nm radiation have been reported: sum-frequency mixing (SFM) of UV and IR wavelengths in beta-barium metaborate 2 , 9 (BBO) and potassium pentaborate,' 0 third-harmonic generation in Sr vapor,' and nonresonant 3 and nearresonant" difference-frequency mixing in Xe. Frequency mixing in gases generally requires extremely high pump intensities to achieve output energies sufficient for practical applications. 3 For short pulses, the high dispersion of BBO makes it difficult to achieve high-efficiency SFM in the VUV range. By using the Sellmeier constants reported by Kato,1 2 the spectral bandwidth for SFM at 193 nm using wavelengths of approximately 266 and 707 nm for a 1-mm-thick BBO crystal can be calculated to be approximately 0.05 nm, which corresponds to an approximately I-ps minimum pulse duration, assuming a Gaussian pulse shape. Thus to generate 193-nm radiation with pulse durations in the subpicosecond range the crystal thickness should be well below 1 mm, which in turn results in decreased conversion efficiency. 2Several schemes for efficient frequency doubling'3-6 and tripling 17 of broadband ultrashort pulses by means of compensating the chromatic dispersion of the nonlinear crystal by angular spectral dispersion have been reported. The methods described in Refs. 13-16 were developed for frequency doubling; consequently, they cannot be used directly for SFM.The tripling scheme of Ref. 17 could also be used for SFM, but its single-beam input design would considerably increase the risk of damage to the dispersive element, and restriction of the input energy in ...

Tilted-Pulse-Front Space-Time Wave Packets

“…So-called “tilted-pulse-front” (TPF) pulses have been critical in the development of many applications in nonlinear and quantum optics . In nonlinear optics, TPF pulses have been utilized in single-shot pulse autocorrelators, arrangements involving traveling-wave excitation, frequency doubling, − and sum-frequency mixing, whereupon the use of a TPF pulse increases the phase-matched bandwidth. − Additionally, TPF pulses were instrumental in the observation of quadratic spatiotemporal solitons. − In quantum optics, the concept of TPF pulses has enabled increasing the bandwidth of photon pairs produced by the process of spontaneous parametric downconversion and has helped reduce the correlations between the photons, such that each photon is in a pure quantum state. − Furthermore, the utilization of TPF pulses in THz applications has led to efficient phase-matching for the generation of intense ultrafast THz pulses by the optical rectification of femtosecond pulses in LiNbO 4 , , thereby enabling femtosecond THz nonlinear spectroscopy. , More recently, TPF pulses have been shown to hold promise for synchronizing the interactions between optical radiation and electrons, whether for particle acceleration, , ultrafast electron microscopy, or X-ray generation. , …”

“…2 So-called "tilted-pulse-front" (TPF) pulses have been critical in the development of many applications in nonlinear and quantum optics. 3 In nonlinear optics, TPF pulses have been utilized in single-shot pulse autocorrelators, 4 arrangements involving traveling-wave excitation, 5 frequency doubling, 6−8 and sumfrequency mixing, 9 whereupon the use of a TPF pulse increases the phase-matched bandwidth. 10−12 Additionally, TPF pulses were instrumental in the observation of quadratic spatiotemporal solitons.…”

Applications of Tilted-Pulse-Front Excitation

“…The reason is that in any tilted pulse front there is present an angular dispersion of the spectral components of the ultrashort light pulse and there is a unique connection between the tilt angle of the pulse front and the angular dispersion (Bor & Rácz, 1985, Martínez 1986, Hebling 1996. Angular dispersion was introduced into the excitation beam of so called achromatic frequency doubler (Szabó & Bor, 1990, Martínez, 1989 and sum-frequency mixing (Hofmann et al, 1992) setups in order to achieve broadband frequency conversion and keeping the ultrashort pulse duration. It was pointed out that in non-collinear phasematched optical parametric generators (OPG) and optical parametric amplifiers (OPA) tilted pulse fronts are expected (Di Trapani et al, 1995).…”

Tilted-pulse-front pumping for phase matching and synchronization

“…Angular dispersion was introduced into the pump beam of so-called achromatic frequency doubler [12][13][14] and sumfrequency mixing 15 setups in order to achieve broadband frequency conversion and to preserve the ultrashort pulse duration. It was pointed out that in non-collinear phase-matched optical parametric generators (OPG) and optical parametric amplifiers (OPA) tilted pulse fronts are expected 16 .…”