•  
  •  
  •  

taccor comb


Features Downloads

The taccor comb consists of a powerful 1 GHz turn-key Ti:sapphire laser with a matched dispersion compensation module, super-continuum generation and ultra-stable f-to-2f interferometer. It provides a long-term stable electrical output signal at the carrier-envelope offset (CEO) frequency with at least 35 dB signal-to-noise ratio in 100 kHz bandwidth that is phase-locked to an RF reference with electronics from our partner Menlo Systems. Tight locking of the mode spacing is accomplished using the TL-1000 repetition stabilisation unit. An optional supercontinuum generation module is available to create stable comb light between 520 nm and 1200 nm.

Product Description

Mode spacing

1 GHz

fCEO locking bandwidth

typ. >200 kHz

Useable 800 nm power after stabilization

600 mW/1000 mW

Stability (@1 s)

5×10-13 (RF reference)

2×10-17 (Optical reference)

Tunability of mode position (@375 THz)

up to 20 GHz

Accuracy

Same as reference, 8×10-20 has been demonstrated

Power per 1 GHz mode

(optional SC module)

typ. 100 nW – 1 µW

Residual phase-noise [1 Hz – 1 MHz]

Typ. 300 mrad

 

System layout:

The standard configuration of the taccor comb comes with the comb extension module housing the f-2f interferometer and dispersion compensation mirrors. It provides a long-term stable electrical output signal at the carrier-envelope offset (CEO) frequency with at least 35 dB signal-to-noise ratio in 100 kHz bandwidth that is phase-locked to an RF reference with electronics from our partner Menlo Systems. Tight locking of the mode spacing is accomplished using the TL-1000 repetition stabilisation unit.

The remaining output of the 800 nm taccor output beam that is not required for fCEO detection is made accessible to the user via the output aperture as free space coupled beam. The beam exhibits average powers of up to 1 W (600 mW with the taccor power 8).

With the optional “supercontinuum output”, a second module is added consuming a fraction of remaining output power (typically 600mW). The additional module is equipped with a photonic crystal fibre generating a supercontinuum covering the range 520 – 1200 nm with an average power of up to 200 mW. The output is made accessible to the user either via a free-space or a FC/PC multimode fibre output port.

Other wavelength ranges upon request.

Watch our 'Benefits of GHz mode spacing for frequency comb applications' here.

Laser Quantum’s Ti:sapphire lasers have played a vital role in the development of the frequency comb technology from the very advent of the concept in the late 1990s. The groups around Theodor Hänsch at Max-Planck-Institute for Quantum Optics in Garching and John Hall at the Joint Institute for Laboratory Astrophysics at Colorado University on Boulder, Colorado (who received the Physics Nobel Prize in 2005 partly for the development of the femtosecond laser frequency comb concept) have acquired and used 1 GHz mode-locked Ti:sapphire lasers from Laser Quantum amongst many other early adopters essentially because of their uniquely high mode spacing. The GHz repetition rate provides several advantages outlined below:

Easier mode identification – The measurement of the frequency of an unknown laser is usually done by beating the laser against the nearest mode (with mode index n) of a stabilized frequency comb and measuring the beat frequency fB. If the comb parameters fR (repetition rate), fCEO (carrier-envelope offset frequency) are known then the laser frequency fL is fL=n×fR+fCEO±fB. Removing the ambiguity in the sign of fB is simple and only requires a slight variation of fR. However, it is much more challenging to know the mode index n as its determination requires prior knowledge of fL with a precision of better than fR.  The situation is illustrated below where the unknown laser is represented by the yellow line and the prior frequency uncertainty by the yellow shaded rectangle. It is obvious that the laser frequency can be unambiguously measured in case of a 1 GHz spaced comb but the mode index remains unclear in case of a 100 MHz laser.

Higher power per mode – At a given average power of a comb laser, the power per each mode scales linearly with the mode spacing, simply because there are less modes to distribute the power amongst at higher repetition rates. Hence, high repetition rates are clearly favourable to enhance the signal-to-noise ratio in any application. In fact, for most practical applications there is another factor causing the power per mode to even scale quadratically with the repetition rate. The practical limit to the pulse energy that can be transmitted through the commonly used supercontinuum (SC) fibers in frequency comb applications has been shown to exhibit threshold (typically at ~300 pJ) beyond which nonlinear noise amplification renders the output incoherent and prevents its use. The highest possible power coupled through a microstructure fiber for a 100 MHz comb laser is typically around 30 mW whereas up to 300 mW are possible at 1 GHz without coherence loss, leading to a net 100-fold advantage for the 1 GHz comb. Even higher repetition rates would be favorable, however, values beyond 2 GHz are often prevented by the increased difficulty to obtain an octave-spanning spectrum from the SC fiber and by the fact that many of the required microwave components and instruments for frequency comb applications become either unavailable or very expensive at several GHz.

Higher event rate – Dual comb spectroscopy is a method that employs two mode-locked lasers with a slight repetition rate offset to perform measurements equivalent to Fourier-Transform Infrared Spectroscopy but without need for a long mechanical delay scanner. Hence dual comb spectroscopy can be orders or magnitude faster than classical approaches and more precise. It has been shown that the use of GHz repetition rates versus 100 MHz systems greatly helps to increase the event rate and the duty-cycle (i.e. the fraction of a measurement that carries significant data) of a measurement (Ideguchi et al., 2013) , (Mohler et al., 2017).

Direct mode access – Another unique capability of GHz spaced comb lasers is their ability to create frequency combs whose modes can be directly resolved, either directly or via moderate mode-filtering. The taccor x10 creates a comb with a 10 GHz spacing that can be directly resolved via a simple grating spectrometer. The top image below shows a subset of adjacent 10 GHz spaced modes recorded with a CCD camera. The bottom image shows the same modes but with the centre ones blocked via a spatial filter. Such setups can be used in various scenarios such as arbitrary optical waveform generation, spectral fingerprinting or spectroscopy with isolated modes.

In fact, it has been shown that the power in a single mode from the taccor x10 can exceed 1mW, which is more than enough to perform saturation spectroscopy, e.g. on Rb vapor (Heinecke et al., 2009). The below animation shows a few modes from a taccor x10 resolved after transmission through a Rb vapor cell while the repetition rate is scanned to move across the D2 absorption line.

An application that benefits from a large mode spacing in combination with moderate Fabry-Perot (FP) cavity filtering is the generation of frequency combs for astronomic spectrograph calibration, also called astrocombs. These devices typically require different mode spacing of several GHz at different wavelength bands and favour a source from which all bands can be served while at the same time only moderate filtering is required. Recent work by various groups has shown that comb lasers with 1 GHz repetition rate appear to be near optimal, more information can be found on our Astronomical Spectroscopy calibration.

 

1. Ideguchi T. et al., 2013. Adaptive real-time dual-comb spectroscopy. Nature. Vol 502, p355

2. Mohler K. et al., 2017. Dual-comb coherent Raman spectroscopy with lasers of 1-GHz pulse repetition frequency. Opt. Lett. Vol 42, p318

3. Heinecke D.C. et al., 2009. Optical frequency stabilization of a 10 GHz Ti:sapphire frequency comb by saturated absorption spectroscopy in 87Rubidium. Phys. Rev A80, 053806

Tunable frequency comb

In its standard configuration, the taccor power is the driving source behind the 1 GHz spaced taccor comb system and it has a centre wavelength near 800 nm before supercontinuum (SC) generation. However, some customers have asked us to supply a tunable drive laser which enables them to either have a phase-stabilised high power output at the tunable laser wavelength and/or to tailor the output of a supercontinuum fiber to specific needs via tuning the input wavelength to the SC. This has been realized using a taccor tune 10 for a wavelength range from 770 nm to 790 nm to be used an application in quantum optics. The image below shows counter records of the locked offset frequency near the edges of the tuning range of this system as an example.

 

The limitation in available operation bandwidth to ~20 nm arises from the ability to create sufficient light for the f-2f interferometer. However, it is possible to shift the available window, for example to 840 nm to 860 nm using an adapted SC fiber and interferometer.

Tailored SC output

We have worked with SC fiber manufacturers to facilitate customer requests for tailored output spectra. The below example shows the result of an effort to get light between 500 nm and 550 nm with less than 5 dB power variation. The average power from the fiber was 115 mW and the power per mode is between 100 nW and 1 µW between 495 nm and 840 nm, an unprecedented value compared to systems with lower repetition rates.

Related Products



Recently Viewed Products


Top