Frequently Asked Questions About Our Products
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Contents
1. Q: What are the
benefits offered by your products?
3. Q: How can I tell
if the pulse measurement made by MIIPS is reliable?
4. Q: What are the
main differences
between the different pulse shapers you offer?
5. Q: What is
included with femtoFit®, femtoJock®, and MIIPS®
Box640 systems?
6. Q: What
customization options are available?
7.Q: What is the
throughput of your instruments?
8.Q: What is the
damage threshold and hence maximum input laser power?
9.Q: How do your
products compare to Coherent’s Silhouette?
10.Q:
How do your products compare to FASTLITE AOPDF pulse shapers?
11.Q:
What if I need to adjust the pulse shaper’s spectral range or use it in a
different setup?
1. Q: What are the benefits offered by your products?
BSI’s produces the only instruments capable of automated
pulse compression. This means that with a simple click of a button the system
measures pulse dispersion (including high order) and compensates the measured
dispersion in order to obtain transform limited pulses, typically within less
than 1% of the theoretical Fourier transform limit. This process is completed
within less than a minute (depends on the system resolution and laser characteristics)
and involves no moving parts.
The immediate advantage is that without the need of a laser
expert, the femtosecond laser performs at its theoretical best. This is
especially important because optics used to deliver the laser beam to the
sample (lenses, mirrors, and microscope objectives) can introduce significant
dispersion. Our instruments eliminate this dispersion automatically.
For users interested in controlling the laser pulses (phase,
amplitude or polarization) the systems are able to control these parameters
with one important advantage. That the pulses are first compressed to the
transform limit, that is, that the pulses have a flat phase at the sample. This
is very important in order to achieve reproducible results. The user then has
the option to introduce essentially any phase amplitude or polarization.
Our systems are compatible with any femtosecond laser, any
wavelength and any energy with little or no customization. Contact one of our
application scientists to determine how one of our instruments could improve
your results and open a world of possibilities.
2.
Q: What is MIIPS®?
MIIPS is a method to measure the spectral phase of a
femtosecond laser. MIIPS is unlike other methods. Instead of relying on
interferometry like all other methods (FROG, SPIDER, MOSAIC, PICASSO etcetera),
MIIPS takes advantage of the fact that second harmonic generation (SHG)
involves the simultaneous sum of multiple frequencies. The phase between
multiple paths to generate a particular SHG frequency determines if they add up
constructively (if the phase is zero) or destructively (if the phase is pi).
Therefore, without the need of using beam splitters and combining the pulses
after an optical delay line, MIIPS is able to measure the spectral phase with interferometric precision.
During MIIPS the instrument delivers a set of calibrated
reference phases and records the SHG spectrum obtained for each of the phases.
The data obtained is sufficient to directly determine the second-derivative of
the spectral phase of the pulse without the need for a retrieval algorithm. The
phase is then obtained by double integration.
The cool part is that the pulse shaper can then introduce a
complementary phase that cancels the phase distortions and renders the pulses
transform limited.
A few additional points to note:
a. It is a single-beam technique (no beam splitting and
recombining); the shaper becomes a part of the experimental setup and ensures
the pulses are exactly what as desired at the location of the sample.
b. It is based on adaptive optics and can correct for
high-order phase distortions, day-to-day variations due to realignment of the
source, or changes in the setup.
c. It has a simple, straightforward SHG detection (a
nonlinear crystal, a filter, and a spectrometer). One can get compressed pulses
right at the sample. It is just a matter of where one places the detection unit.
d. The same hardware is used for both measuring and
correcting phase distortions. No additional instrumentation is needed. Note
that a single pulse shaper can substitute a number of dedicated optical
elements such as prism- and/or grating-based pulse compressors, chirped
mirrors, tunable filter, an optical delay line, pulse measurement devices, etc.
e. While the instrument works in the frequency domain (laser
spectrum + spectral phase) the output is modulated in the time domain.
Therefore, the instrument easily generates pulse pairs that can be scanned with
attosecond precision. Using this capability, the system gives you the
capability of measuring interferometric
autocorrelation or interferometric FROG traces.
3.
Q: How can I tell if the pulse measurement made by MIIPS is reliable?
Since the first publication about MIIPS (ref OE article and
first Optics Letters), the results have been compared to those obtained by
other pulse measurement methods. It is important to note that MIIPS is so
accurate that it has been used to measure the dispersion of several materials
(water, air, multiple gases and solvents [GIVE REFERENCE FOR EACH] with greater
accuracy than obtained by white light interferometry. MIIPS has also been
compared by an independent lab with other conventional pulse measurement
methods [Bartell]. No other pulse characterization method is capable of
achieving higher accuracy or precision dispersion methods than MIIPS.
After MIIPS, the instrument can easily generate pulse pairs
that can be scanned with attosecond precision. Using this capability, one is
able to obtain interferometric autocorrelation or interferometric FROG traces. These can be directly compared
to the Fourier Transform of the laser output to confirm the pulses measured.
Finally, the SHG spectrum can also be compared to the
theoretically calculated SHG spectrum based on the laser output. Provided the
spectrum is not affected by filtering effects in the optical path, there should
be a perfect correspondence.
4. Q:
What are the main differences
between the different pulse shapers you offer?
All our pulse shapers are based on a folded-4f configuration,
where the light is spectrally dispersed and recombined by a grating. The
spectral phase (and amplitude) is manipulated by a high-quality, linear
liquid-crystal spatial light modulator (SLM). The instruments vary in
capabilities, optics size but more importantly – the SLM used. The SLM can be
single-mask (for phase-only shaping) or dual-mask (for phase & amplitude or
polarization shaping), with 128 or 640 independently addressable pixels. All of
our systems include computer controller, MIIPS 2.0
software, SHG detection unit, and compact spectrometer.
MIIPS®Box 640PA: This is the
best commercial pulse shaper in the world. Featuring a dual-mask 640-pixel SLM,
enables independent phase and amplitude (or polarization) control over the
optical waveform. It delivers enhanced dispersion management capabilities, high
spectral resolution, and is suitable for a variety of pulse shaping
applications. The system’s spectral range is configured to fit the customer’s
laser source parameters and optimize the use of (12 bit)^(640x2)
degrees of freedom.
MIIPS®Box 640P: This system offers the highest resolution phase control, using a single-mask 640-pixel SLM. It rivals the
capabilities of the top-the-line system for applications that do not require
amplitude shaping. The system’s spectral range is configured to fit the
customer’s laser source parameters.
femtoJock® PA offers the best cost-to-value ratio. Equipped with a
dual-mask 128-pixel SLM, it retains the independent control of both phase and
amplitude, offers good spectral resolution, and comes configured to fit the
customer’s laser source specifications. It is an excellent choice for pulse
compression and most pulse shaping applications.
femtoJock® P is a phase-only pulse shaper with a single-mask 128-pixel
SLM. It is a cost-effective solution for pulse compression and pulse shaping
applications that do not rely on amplitude shaping. The instrument
configuration is tailored to fit the customer’s laser source specifications.
femtoFit® is the smallest instrument in its class, designed for
embedding and other OEM applications. Its single-mask 128-pixel SLM and other
components fit within a 6-inch cube, reducing the instrument’s footprint and
cost but limiting customization options. This phase-only pulse shaper
comes only in two pre-set configurations, optimized for common Ti:Sapphire laser sources.
5. Q:
What is included with femtoFit®,
femtoJock®, and MIIPS® Box640
systems?
Every system includes
a. The pulse shaping
instrument with the pre-set (femtoFit®) or custom (femtoJock®,
MIIPS®Box640) spectral range;
b. Free-space SHG detection assembly or a microscope detection unit (per
user’s choice);
c. Miniature spectrometer with
coupling fiber;
d. Laptop computer with
pre-installed MIIPS®2.0 Software Suite;
e. USB flash drive with the MIIPS®2.0 software
installer, instrument drivers, and factory backup files.
6. Q: What customization options
are available?
All of our instruments can be tailored to our customer’s
specifications free of charge if no significant modifications in the hardware
are required. The femtoFit®’s
customization is limited to the choice of two spectral ranges - 750-850 nm and
700-900 nm.
For fairly narrowband laser sources (with pulse durations
>50fs), we recommend to enhance the spectrometer spectral resolution by
upgrading from the standard USB4000 spectrometer bench to HR4000 (Ocean
Optics). Occasionally, two spectrometers are needed to span over both the
fundamental and SHG ranges. A variety of Ocean Optics and Photon Control
spectrometers are supported and can be added for extended wavelength range
coverage or enhanced detection sensitivity.
Upon the user’s request, the pulse shaper can be
pre-calibrated at the factory for several spectral ranges, which can be tuned
to by rotating the grating manually or even by swapping between different gratings.
We also offer automated tuning capability, based on a computer controlled
rotation stage. The rotation stage is interfaced with the software and is tuned
by setting the desired laser wavelength.
If you haven’t found what you are looking for, please
contact us. We invite you to take advantage of our extensive (more than eight
years) experience. One of our Applications Scientists will work with you tailor
a solution for your application.
7.Q: What is the throughput of
your instruments?
The throughput depends on the selected spectral range and is
limited primarily by losses introduced by the grating and to a lesser extent the
SLM.
For the 700-900 nm range, common for Ti:Sapphire lasers, the throughput of 45-55% is
typical. The double-reflection on the grating leads to 20-30% loss. A double
pass through the SLM mask accounts for another 15-20% of insertion losses.
One advantage of the 4f pulse shaper design is that all the
pulses are identically shaped independent of laser repetition rate, without need
for synchronization. If throughput is of great concern speak to one of our
Applications Scientists to determine if we are able to meet your requirements.
8.Q: What is the damage threshold
and hence maximum input laser power?
a. For a typical 1-kHz Ti:Sapphire regen. amplifier
128-pix. SLM - <50-60 mW (i.e., 50-60 uJ/pulse); permanent damage for 120 mW.
640-pix. SLM - <250-300 mW
(i.e., 250-300 uJ/pulse); permanent damage >450mW.
b. for a 75-MHz Ti:Sapphire
oscillator and
128-pixel SLM - <500 mW;
640-pixel SLM – no data; a conservative estimate is 1-2W.
The underlying assumption is that the laser spectrum
(bottom-to-bottom) is spread across the entire SLM. We have designed pulse
shapers that can take much higher laser energies. Please contact one of our
Applications Scientists to determine if we are able to meet your requirements.
9.Q: How do your products
compare to Coherent’s Silhouette?
As you may already know, the Silhouette pulse shaper was a
revolutionary product designed by Coherent, Inc. in 2005 incorporating the
MIIPS-based automated pulse compression from Biophotonic Solutions, Inc. (BSI),
and introduced commercially in 2006, under a three-year agreement between the
two companies. The product is no longer available.
Below is the point-by-point comparison of BSI’s products
with the Silhouette:
A. Silhouette is a folded-4f pulse shaper
based using a prism as a dispersive element. BSI’s instruments are also based
on the folded-4f geometry but they utilize gratings to disperse the beam at the
Fourier plane (at the SLM). Due to the prism, Silhouette has an edge in terms
of the throughput efficiency (~70% vs. 45-55%) but the prism-based design
is at a disadvantage when it comes to
a. optical resolution at the SLM, which
affects the range of time delays and chirp magnitude the shaper can handle;
b. flexibility to be tailored to a specific
laser source. Silhouette was designed to work with Coherent’s
Ti:Sapphire lasers and can be configured for two
pre-set spectral ranges (100 nm or 200 nm wide when centered at 800 nm) by
changing the beam path length, which often doesn’t give you the full coverage
of SLM pixels. BSI’s pulse shapers are configured to optimally fit the laser
source by picking a proper grating/focal-length combination. They can also be
upgraded to provide automated tuning through motorized rotation of the grating;
c. alignment simplicity (when using
gratings, one doesn’t need to consider Brewster’s angle; the grating angle is
defined by the spectral range the user wants to cover).
B. Silhouette is based on a
dual-mask 128-pixel SLM from CRi (now a part of PerkinElmer). BSI offers
several shaper platforms to choose from. The top-of-the-line MIIPS®Box 640PA system features a
dual-mask 640-pixel SLM. The entry-level FemtoFit® and
femtoJock® P shapers come with a single-mask 128-pixel SLM.
C. Silhouette is equipped with an
integrated SHG detection unit. BSI offers two options: a free-space assembly
and an integrated microscope detection unit (MDU), which is designed to be
placed directly at the focal plane of a microscope objective.
D. Silhouette uses the earliest version of
the MIIPS® software. BSI released the superior MIIPS®2.0
software in Fall 2011. It
features new MIIPS®
modalities, hot-swapping of multiple spectrometers, enhanced push-button
calibration routines, and improved user interface (check out the videos on
YouTube http://www.youtube.com/watch?v=ukZpQFvCezk). For advanced ultrafast laser users and
developers, the new software offers streamlined acquisition of interferometric and non-interferometric
frequency resolved autocorrelations and has several other built-in pulse
shaping applications.
BSI offers upgrade paths for owners of the
Silhouette system. Contact one of our Applications Scientists for more
information.
10.Q: How do your products compare to FASTLITE AOPDF pulse
shapers?
Compared to AOPDF
products, our systems have a higher throughput, are independent of laser
repetition rate, have higher spectral resolution, can handle a much broader
bandwidth, can handle higher intensity input pulses, permit discontinuous phase
functions, include auto-calibration software and include the MIIPS software for
automated pulse compression.
The principle of
operation of the two systems is similar but with one important difference. They
are similar because both require the separation of spectral frequencies in
space in order to be able to shape the spectral phase. Our systems are based on
the reflective 4f design, where the spectrum is dispersed onto a direction in
space that is perpendicular to that of laser propagation. At that point, known
as the Fourier plane, one is able to design the optimal resolution in order to
ensure ideal pulse shaping. The AOPDF systems disperse the frequencies along
the propagation direction. This places a number of restrictions on spectral
resolution and on the range of phases that can be delivered [these have been
documented in the literature Ref Ben Whitaker]. The output from an AOPDF shaper
is the fraction of the laser pulse that is diffracted along the desired
direction. This reduces the throughput to below 35%. Because the AO crystal is
modulated in the time domain, laser pulse synchronization with the waveform
generator is critical.
11.Q: What if I need to adjust the pulse
shaper’s spectral range or use it in a different setup?
No problem! The software
that comes with every BSI’s pulse shaper features automated calibration
routines (wavelength vs. SLM pixel, phase vs. SLM voltage), enabling the user
to re-calibrate the instrument for the same or different spectral range
on-site. If the spectral range is to be adjusted manually, one can rotate the
installed grating or put a different one (BSI provides gratings mounted on appropriate
holders). In our femtoJockâ and
MIIPSâBox640
systems, the post holder for the grating allows doing so without significant
realignment of the shaper. Better yet, their input and output ports are in-line.
So, one can pull in and out the whole pulse shaper, without disturbing the
experimental setup.