Whitepaper: Shortest CEP stabilised Ti:Sapphire pulse
Figure 2: An image of the Finesse 6 Pure (Laser Quantum Ltd) pumping an octave-spanning
VENTEON | PULSE : ONE femtosecond oscillator
October 03, 2012
Abstract: A dual-output, self-synchronised,
CEP-stabilised Ti:sapphire oscillator
is presented, with a pulse duration of
4.4fs and a CEP phase noise of < 100
mrad using a Finesse 6 Pure pump laser.
Since the first demonstration of the gain
material Ti:sapphire as a tuneable laser
medium, there has been much interest in the
exploitation of its broadband optical output,
chief among which is the generation of ultrashort
optical pulses. Since the pulse duration is
inversely proportional to the optical bandwidth
supported by the Ti:sapphire oscillator,
careful attention must be paid to the optical
design to compensate for dispersive effects.
The generation of sub-20 femtoseconds
pulses (fs or 10-15 seconds) is now routinely
demonstrated and has been commercially
available for several years. In recent years,
however, the pulse duration has been driven
down to sub-10 fs by exploiting the full
bandwidth of the Ti:sapphire crystal. Once the
pulse duration is reduced to sub-6 fs, there are
only approximately two cycles of the electric field
within the envelope of the optical pulse. Figure
1 shows a comparison of two femtosecond
pulses, their pulse envelope plotted with
the corresponding electric field oscillation.
Figure 1: A comparison of two femtosecond pulses with
the corresponding electric field oscillations. In the fewcycles
pulse shown, the Ti:sapphire centre frequency
of 375 THz, a wavelength of 800 nm respectively, the
period of the electric field oscillation is 2.7 fs.
It can be seen that the number of contributing
field oscillations supported by the longer pulse -
which is already as short as 15 fs - is significantly
higher than for the few-cycle femtosecond
pulse. By stabilizing the carrier envelope phase
(CEP, φ0 ), the electric field of such few-cycle
pulses can be controlled opening up for novel,
significant ultrafast experiments such as high
harmonic generation and attosecond science.
Using a Finesse Pure 6 W pump source at 532
nm from Laser Quantum Ltd, integrated into
a common water-cooled platform, VENTEON
Laser Technologies GmbH has demonstrated
an octave-spanning direct CEP-stabilised
output of well below 5 fs without the need
for additional spectral broadening (Figure 2).
This system delivers the shortest commercially
available pulses directly from a Ti:sapphire
oscillator, with a SPIDER characterised
pulse as short as 4.4 fs as shown in Figure 3.
Figure 3: A SPIDER characterized pulse of 4.4 fs is
shown: the shortest commercially available pulse from
a CEP-stabilised Ti:sapphire laser
The CEP phase noise of those pulses is less than
100 mrad. This requires a minimal amplitude
noise of the Finesse Pure within the whole
noise spectrum. With RMS noise significantly
less than 0.03% (10 Hz to 100 MHz), the
Finesse Pure is ideally suited to this purpose.
This laser system is directly applicable for
optical parametric chirped pulse amplification
(OPCPA) applications, since its octave-spanning
spectral bandwidth allows the system to be
equipped with two separate outputs which
are intrinsically self-synchronised with ultralow
timing jitter. The first output can provide
CEP-stable broadband sub-6 fs signal pulses;
the second narrowband output at a centre
frequency of 1030 nm can deliver a pulse
energy of > 30 pJ in a spectral bandwidth of
10 nm (FWHM) and is an ideal seed for Ybdoped
amplifier stages used for pumping
NOPA stages of an OPCPA amplifier system.
In such an OPCPA amplifier system, the
ultrashort pulse duration of the sub-6 fs
signal seed pulses can be preserved and
amplified up to multi-μJ pulse energies
making an ideal source for high harmonic
generation and ultrafast spectroscopy.
Acknowledgements: Dr Stefan Rausch and Dr Thomas Binhammer of VENTEON Laser Technologies GmbH and Dr Lawrie Gloster
of Laser Quantum Ltd.
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