Mesa Photonics

News

September 1, 2007
Mesa Photonics releases a new ultrafast laser pulse measurement system based on frequency resolved optical gating: FROG Scan

Mesa Photonics is pleased to announce the issuing of US Patent 7,130,052.

To the right is a pulse with pure cubic spectral chirp.   As with the case when cubic spectral chirp is added to a pulse, ringing occurs in the time domain representation of the pulse.  In an autocorrelation, this ringing shows up as smooth wings extending beyond the central peak.  You can clearly see that the main pulse width is less than 80 fs while the ringing extends past 500 fs.  Also notice that the pi phase steps at every pulselet are clearly defined.

Pictured on the left is the screen capture of VideoFROG FROG scan measuring a pulse with fourth, fifth, and sixth order components of the spectral phase.  In addition, the center portion of the spectrum is removed.  The main portion of the pulse is about 70 fs wide while the pedestal spans about 1 ps.  The ringing on the left portion of the central peak is indicative of odd order phase.  Here, the entire pedestal of the pulse extends over 1 ps, which demonstrates the power of the completely tunable optical delay in the FROG Scan system.

This pulse has large amounts of cubic and quartic spectral chirp--enough to influence of the pulse spectrum because of greater than pi phase shifts in the spectrum.  Notice that to the right of the central pulse, there is some ringing, and to the left, the ringing has a higher frequency.  Also notice that the base of the pulse spans 2 ps!  The added pulses to the left occur because of the large amount of higher order spectral phase.

To generate this pulse, so much quartic spectral chirp was added that the pulse shaper aliased the phase, causing a highly structured spectrum and a poorly defined spectral phase.  The time domain pulse is comprised of three primary pulses that range over about 1.5 ps.  The narrowest of the pulses is about 25 fs in width.  Such level of detail in the wings of the pulse can only be achieved using a 16-bit detector, which gives FROG Scan its unprecedented ability to measure long pulse pedestals underlying short pulses.