UOA09-08: LX SPIDER ultrashort laser pulse measurement device
Submitting InstitutionUniversity of Oxford
Unit of AssessmentPhysics
Summary Impact TypeTechnological
Research Subject Area(s)
Physical Sciences: Optical Physics
Technology: Communications Technologies
Summary of the impact
Invented at the University of Oxford, an instrument for measuring the
temporal shape of ultrashort laser pulses has delivered new capabilities
for users and manufacturers of short-pulse lasers. The device, the LX
SPIDER, is smaller, cheaper and more sensitive than its predecessor. Its
impact has been realised by licensing patented technology to APE GmbH, who
brought the LX SPIDER to market in 2008. Customers are from industrial and
research institutions globally and the device has brought benefits to
users in a variety of sectors including materials processing and
biomedical diagnostics. It is also used by manufacturers of pulsed lasers
in the specification, verification and installation of their laser
The research implements, in a new and simpler way, the concept of
spectral-shearing interferometry, a means to use nonlinear optics to
determine the electric field envelope of an optical pulse using a
deterministic algorithm. In its original incarnation, the Spectral Phase
Interferometry for Direct Electric field Reconstruction (SPIDER) method
was developed by Professor Ian Walmsley while at the University of
The SPIDER technique requires a pair of pulses (the unknown input or
'test` pulse and a time delayed copy) and another pulse, derived from the
same input pulse, which is strongly temporally broadened (`chirped'). A
nonlinear interaction, sum frequency generation, between the long chirped
signal and the test pulses, within a crystal, results in a frequency shift
between the pair. The optical spectrum of the combined signal of the two
pulses reveals the spectral
phase, as a function of frequency, and thus complete pulse
Although the SPIDER technique worked well, there were a number of
features that if simplified would make the instrument smaller, more robust
and more sensitive. After his arrival in Oxford in 2001, Walmsley set
about simplifying the design. His research at Oxford produced a series of
improvements resulting in a device that was smaller and easier to
integrate into existing laser systems, which enabled its uptake across a
wider group of users.
Walmsley realised the device could be made significantly simpler by
reconfiguring the nonlinear optical process used to generate the spectral
shear (that is, the differential frequency shift between two replicas of
the test pulse spectrum). He designed a phase-matching arrangement that
enabled the spectral shearing to be done in a single step with one
crystal, without needing the chirped signal . The key concept,
group-velocity matching, was also shown theoretically to be very generally
applicable to all nonlinear optical processes . Group-velocity matching
eliminated the need for the chirped pulse and therefore the optics that
produced it, including a bulky and inefficient pulse stretcher [3,4].
In SPIDER, the crystal length was limited by the chirped signal, which
travelled through the crystal at a different speed to the other two pulses
and thus short crystals were used to minimise blurring in the spectral
shear. By removing the need for the chirped signal, all pulses travel with
the same velocity in a single crystal. Walmsley realised he could then use
a longer crystal to perform the sum frequency generation, which would
result in a dramatic increase in frequency conversion efficiency, and thus
improve the sensitivity of the device. The long crystal (LX) method had a
further advantage that the longer, thicker crystals were more robust and
The research was led in Oxford by Professor Ian Walmsley (2001 - present)
with Gorza (postdoctoral researcher 2005 - 2007), Wasylczyk (postdoctoral
researcher 2006 - 2007) and research students Kosik-Williams and Radunsky.
The improvements from the Oxford research described in ,  and 
culminated in a new technique, named ARAIGNEE, which was patented in the
US (US7599067, filed 2006, granted 2009) and in the EU (EP1886107, filed
2006, granted 2011). The inventors were Walmsley, Gorza and Radunsky and
the patent was filed by Isis Innovation, the University of Oxford's
technology transfer office.
References to the research
(Oxford authors, *
denotes best indicators of quality)
* Radunsky A, Kosik Williams EM, Walmsley
IA, Wasylczyk P, Wasilewski W, U'Ren AB and Anderson M, (2006),
Simplified spectral phase interferometry for direct electric-field
reconstruction by using a thick nonlinear crystal, Optics Letters,
31, doi: 10.1364/OL.31.001008, citations: 16 (Scopus).
 Gorza S-P, Radunsky
AS, Wasylczyk P
and Walmsley IA, (2007),
Tailoring the phase matching function for ultrashort pulse
characterization by spectral shearing interferometry, Journal of the
Optical Society of America B, 24, 2064, doi:
10.1364/JOSAB.24.002064, citations: 3 (Scopus).
* Radunsky AS, Gorza S-P, Wasylczyk
P and Walmsley IA,
(2007), Compact spectral shearing interferometer for ultrashort pulse
characterization, Optics Letters, 32 181, doi:
10.1364/OL.32.000181, citations: 9 (Scopus).
* Gorza S-P, Wasylczyk P and Walmsley
IA, (2007), Spectral shearing interferometry with spatially
chirped replicas for measuring ultrashort pulses, Optics Express,
15, 15168, doi: 10.1364/OE.15.015168, citations: 10 (Scopus).
Details of the impact
The ability to monitor and optimise the operation of lasers simply and
reliably is important in many sectors and for some problems it is
essential to know the temporal shape of the pulse. Walmsley and his group
knew that a new device would have commercial appeal if they could reduce
its size so it became smaller than the laser itself, and simple and
reliable enough to be used by non-specialists. This demanded a simplified
The research at Oxford resulted in a number of commercial advantages of
this technique over its predecessor:
- The reduction in optical components by eliminating the need for
- reduced the device's physical size to less than that of a shoebox (10
- simplified the installation process.
- reduced the cost of fabrication.
- increased the operational lifetime.
- enabled its use by non-expert users.
- The use of a longer crystal
- increased the sensitivity by a factor of 10 (pulse lengths of 16fs -
300fs can be measured).
- improved the robustness.
New product brought to market
The Oxford research was commercialised through an exclusive license to
German company, APE GmbH. APE specialise in devices for generation,
manipulation and measurement of ultrashort laser pulses. APE have 55
employees, and sell products for the ultrafast laser market, directly and
through distributors (e.g. Vereon, Newport, Thorlabs, Photonics Industry)
in 40 countries.
Building on the licensed technology, APE introduced automatic calibration
further simplifying the design. The new device, LX SPIDER, was brought to
market in May 2008. The product is supporting a small group within APE
that is dedicated to laser pulse metrology and the LX SPIDER represents
between [text removed for publication] of APE's total sales. It
retails at approximately [text removed for publication] and [text removed for publication]
units have been sold to large and small
companies as well as research institutions [A]. LX SPIDER is now the most
common commercially-available method for full characterisation of the
electric field of ultrashort laser pulses.
Benefits to laser manufacturers
Due to the commercialisation of the Oxford research and subsequent
commercial availability through APE of the LX SPIDER, laser performance
can now be specified more completely and easily than was possible a decade
ago. Specification of the pulse shape, as well as its duration, in order
to verify that the pulse is as short as possible is now routinely expected
by buyers of lasers.
Companies who manufacture and sell lasers have used the LX SPIDER to
specify their lasers and incorporated its use into their verification
protocol. For example, Coherent Inc., one of the largest laser
manufacturers and a leading producer of short pulse lasers and amplifiers,
uses LX SPIDER units as a diagnostic tool in their R&D to verify laser
operation, to adjust the laser configuration before shipping and during
Coherent said that the LX SPIDER "not only gives the pulse duration,
but also spectral phase information, which simplifies and streamlines
the alignment of compressor parameters in order to achieve best possible
compression of amplified pulses. Spectral phase information also allows
for a fast identification of possible issues with optics coatings, that
are not meeting our specs, or even mirror surface flatness issues on
optics that see spectrally spread beams." [B]
Benefits to other end users
Ultrashort optical pulses are used in many applications, including
advanced microscopy, materials processing (including photonic components
for communication and sensing) and biomedicine. A method for pulse
characterisation provides end users with more reliable processes and
results. Where high levels of precision are required, introducing an LX
SPIDER into the experimental configuration has allowed the user to adjust
the optical pulse accurately.
A major market for the LX SPIDER is the commercial research laboratory
sector where it is used by those performing molecular spectroscopy and
microscopy, including the study of molecular dynamics in physical
chemistry, transport studies in biology and for developing solar cells.
Another important set of applications is in nonlinear microscopy, used
especially in biology. Knowing and controlling the shape and duration of
the ultrashort optical pulses used in these techniques is vital to the
generation of high-quality images, since the efficiency of the nonlinear
processes that underpin these techniques depends on the peak intensity of
the input laser pulses.
Sources to corroborate the impact
[A] Letter from Sales Manager at APE GmbH (held on file) confirms sales
and licensing information.
[B] Statement from Senior Development Engineer at Coherent Inc. (held on
file) confirms Coherent's use of the LX SPIDER in their R&D and