1 / 14

Description of a pulse train

To the change in phase between successive pulses. corresponds a frequency::. t RT. j e. Electric field. Time. Description of a pulse train. The “ideal” mode-locked laser emits a train of identical pulses:. The change in phase from pulse to pulse is a measurable quantity,

shakti
Download Presentation

Description of a pulse train

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. To the change in phase between successive pulses corresponds a frequency:: tRT je Electric field Time Description of a pulse train The “ideal” mode-locked laser emits a train of identical pulses: The change in phase from pulse to pulse is a measurable quantity, independent of the duration of the individual pulse in the train.

  2. je je jp = (i + 1) - (i ) Description of a pulse train A train of d-functions tRT je Electric field Time Electric field nav jp Frequency f0= 1/tRT 2ptRT

  3. // jp f0= je je jp 2ptRT = (i + 1) - (i ) Description of a pulse train A train of pulses tCoherence tRT je t Electric field // Time Dn =1/tCoherence Dnb =1/t Electric field nav Frequency 1/tRT

  4. jp jp f0= je je jp 2ptRT = (i + 1) - (i ) Description of a pulse train The mode comb Dn =1/tCoherence Dnb =1/t Electric field nav Frequency 1/tRT

  5. Tuned cw laser: the mode spacing varies with frequency Unequally spaced teeth D l counter 2Ln(l)/c (a) l 200 Mode locked laser comb: Spectro. Rep. Rate - 101 884 000 Hz D fixed teeth spacing. 100 counter 700 800 900 Fixed number Wavelength [nm] Mode-locking = Laser Orthodontist

  6. Evolution of a single pulse in an ``ideal'' cavity How unequally spaced modes lead to a perfect frequency comb Two burning questions: As a pulse circulates in the cavity, Which mechanism makes the does it evolve towards a steady state? unequally spaced cavity modes equidistant?

  7. Dispersion Kerr-induced chirp Evolution of a single pulse in an ``ideal'' cavity Kerr effect

  8. How unequally spaced modes Group delay not equally spaced because nav = nav(w) Cavity modes: where F.T. where lead to a perfect frequency comb Phase delay Unequally spaced modes, is contradictory to the fact that comb teeth are equally spaced. A cavity with ONLY Kerr modulation generates the pulse train: dispersion

  9. Evolution of a single pulse in an ``ideal'' cavity How unequally spaced modes lead to a perfect frequency comb Two burning questions: Which mechanism makes the As a pulse circulates in the cavity, unequally spaced cavity modes does it evolve towards a steady state? equidistant? SAME CONDITION

  10. The choice of the optimum metrology method for a given problem The right tool for a given measurement: An overview The pulse train

  11. The right tool for a given measurement An overview THE PULSE TRAIN TOOLS: Simple analog oscilloscope and frequency doubling crystal. Electronic Spectrum analyzer Spectrometer What to look for? Both fundamental and second harmonic: a straight line. No sideband and higher harmonics Continuous spectrum, central wavelength

  12. The right tool for a given measurement An overview THE PULSE TRAIN Both fundamental and second harmonic: a straight line. Electronic Spectrum analyzer

  13. The right tool for a given measurement An overview THE PULSE TRAIN What we should not see: Modulation of the train on a ms scale Q-switched-mode-locked train (Shows as a sideband on spectrum analyzer on a 100 KHz scale)

  14. The right tool for a given measurement An overview THE PULSE OF A TRAIN Do you want to tune the laser to get the shortest pulse? TOOLS: Scanning autocorrelator, Intensity, interferometric, spatially encoded Spider Tuning a high power system Tuning a laser oscillator Single pulse characterization at high repetiton rate: SPIDER

More Related