BioPhotonic Produtcs

Frequently Asked Questions About Our Products

What are the benefits offered by your products?

BSI 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.

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:

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.
How can I tell if the pulse measurement made by MIIPS is reliable?

Since the first publication about MIIPS [ref1, ref2], 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 and seawater, air and multiple gases, solvents, even metamaterials) with greater accuracy than obtained by white light interferometry. MIIPS has also been compared by an independent lab with other conventional pulse measurement methods [ref3]. 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.

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.

MIIPSBox640: 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.

MIIPSBox640-P: 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 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.

What is included with femtoFit, femtoJock, and MIIPSBox640 systems?

Every system includes:

  • The pulse shaping instrument with the pre-set (femtoFit) or custom (femtoJock, MIIPSBox640) spectral range

  • Free-space SHG detection assembly or a microscope detection unit (per user's choice)

  • Miniature spectrometer with coupling fiber

  • Laptop computer with pre-installed MIIPS 2.0 Software Suite

  • USB flash drive with the MIIPS 2.0 software installer, instrument drivers, and factory backup files.
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 experience. One of our Applications Scientists will work with you tailor a solution for your application.

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.

What is the damage threshold and hence maximum input laser power?

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.

For a 75-MHz Ti:Sapphire oscillator

  • 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.

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 femtoJock and MIIPSBox640 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.

If you haven't found the answer to your question, please send an e-mail to moc.otmefisb@ofni