Ul­tras­hort pulse ge­ne­ra­ti­on

Se­mi­con­duc­tor la­sers are a key tech­no­lo­gy in the tel­e­com­mu­ni­ca­ti­ons sec­tor. The fea­ture of di­rect elec­tri­cal­ly pum­ping al­lows for a fast mo­du­la­ti­on of the laser in com­bi­na­ti­on with a very com­pact setup. Howe­ver, in other areas like ul­tras­hort pulse ge­ne­ra­ti­on the bre­ak­th­rough of se­mi­con­duc­tor la­sers is yet to come de­s­pi­te of their enor­mous ad­van­ta­ges. Table 1 shows a com­pa­ri­son bet­ween solid state, fibre and se­mi­con­duc­tor la­sers. It can be seen that the cur­rent se­mi­con­duc­tor laser date com­pa­re to the other la­sers badly in the most re­le­vant points like pulse du­ra­ti­on and aver­a­ge out­put power. The aim of this re­se­arch pro­ject is to close the gap bet­ween com­mer­ci­al­ly avail­able laser sys­tems and se­mi­con­duc­tor la­sers to crea­te an al­ter­na­ti­ve, which has the po­ten­ti­al to re­vo­lu­tio­ni­ze the mar­ket for fem­to­se­cond laser sys­tems.

 Table 1: Com­pa­ri­son of fem­to­se­cond laser sys­tems

 Solid state laserFiber laserSe­mi­con­duc­tor laser
Min. pulse width++\+  \-  
Out­put power++    \+\-
Fle­xi­bi­li­tyre­pe­ti­ti­on rate\+0++
Fle­xi­bi­li­tywa­ve­length\+ \-++
Com­pact­ness-- \+++
Cost--  0\+

Since the end of the 1980’s there is an in­ten­se on­go­ing re­se­arch of se­mi­con­duc­tor la­sers as a sour­ce for ul­tras­hort laser pul­ses. But the com­plex car­ri­er dy­na­mics in the se­mi­con­duc­tor ma­te­ri­al doesn’t allow the di­rect ge­ne­ra­ti­on of fem­to­se­cond pul­ses with high aver­a­ge out­put power from an elec­tri­cal­ly pum­ped se­mi­con­duc­tor laser. Thus, we have de­ve­lo­ped a mo­du­lar sys­tem con­cept as de­pic­ted in fi­gu­re 1: in an oscil­la­tor based on a two sec­tion laser diode in an ex­ter­nal ca­vi­ty pul­ses with a du­ra­ti­on of 5 ps are ge­ne­ra­ted. The re­so­na­tor geo­me­try al­lows the com­pen­sa­ti­on of the car­ri­er dy­na­mics in a fa­shion that the spec­tral band­width is great­ly in­crea­sed, while the pulse du­ra­ti­on stays in the ps-re­gime.

This enables the am­pli­fi­ca­ti­on by an op­ti­cal am­pli­fier which is also an elec­tri­cal­ly pum­ped se­mi­con­duc­tor de­vice. In a se­cond step the pulse is com­pres­sed by an ex­ter­nal pulse com­pres­sor to some 100 fs. The usage of se­mi­con­duc­tor de­vices enables the pos­si­bi­li­ty to build the whole laser with a foot print as small as 300 * 300 mm². Fi­gu­re 2 shows the com­pact fem­to­se­cond diode laser sys­tem in front of a com­mer­ci­al Ti:Sapp­hi­re laser sys­tem. All com­po­n­ents to ge­ne­ra­te high power laser pul­ses are in­clu­ded.


The re­so­na­tor in­ter­nal dis­per­si­on con­trol al­lows to ge­ne­ra­te pul­ses with a du­ra­ti­on as short as 158 fs. These are to our know­ledge the shor­test pul­ses which were ge­ne­ra­ted by an elec­tri­cal­ly pum­ped se­mi­con­duc­tor laser. This clo­ses the gap to fibre and solid state laser sys­tems. After the pulse am­pli­fi­ca­ti­on pulse en­er­gies up to 2 nJ are ge­ne­ra­ted. This leads to a peak power of 6.5 kW. Table 2 sum­ma­ri­zes the spe­ci­fi­ca­ti­ons of the laser sys­tem. Table 3 is the mo­di­fied ver­si­on of table 1 with re­spect to our ac­tu­al re­se­arch re­sults.

Table 2: Spe­ci­fi­ca­ti­ons of the pro­to­ty­pe

 Pulse en­er­gy:

 2 nJ

 Re­pe­ti­ti­ons rate:

 300 kHz bis 1.2 GHz

 Min. pulse du­ra­ti­on:

 160 fs

 Peak power:

 6.5 kW

 Cen­tral wa­ve­length:

 850 nm  

  Foot print:

 300 mm x 300 mm 

Table 3: Com­pa­ri­son of our fs-di­ode laser sys­tem to other fem­to­se­cond laser sys­tems

 Solid state laserFiber laserfs-diode laser
Min. pulse width++/+  /+  
Out­put power ++   /+/+
Fle­xi­bi­li­tyre­pe­ti­ti­on rate/+0++
Fle­xi­bi­li­tywa­ve­length/+ /-++
Com­pact­ness-- /+++
Cost--  0/+

Based on our pre­vious re­se­arch we ex­ten­ded our sys­tem by in­ves­ti­ga­ting a mul­ti­ple-pass am­pli­fi­ca­ti­on sche­me in­s­tead of the sin­gle-pass one. This is per­for­med by im­ple­men­ting the ta­pe­red am­pli­fier in a ad­jus­ta­ble ring ca­vi­ty con­fi­gu­ra­ti­on. The am­pli­fier is then see­ded by an ul­tras­hort pulse from a mas­ter oscil­la­tor. By matching the ca­vi­ties geo­me­tri­cal lengths of mas­ter oscil­la­tor and ring am­pli­fier, re­so­nant pulse am­pli­fi­ca­ti­on re­gime is achie­ved. This pro­ject is fun­ded by the DFG (Deut­sche For­schungs­ge­mein­schaft).


  • [1] M. A. All­oush, R. H. Pilny, C. Bren­ner, T. Przi­war­ka, A. Klehr, A. Knig­ge, G. Tränk­le, M. R. Hof­mann, “Mo­de-lo­cked diode laser with re­so­nant ring am­pli­fier”, SPIE 10682, Se­mi­con­duc­tor La­sers and Laser Dy­na­mics VIII, 106820N (2018)
  • [2] J. C. Bal­zer, T. Schlauch, A. Klehr, G. Er­bert, G. Tränk­le, M. R. Hof­mann, “High peak power pul­ses from dis­per­si­on op­ti­mi­sed mo­de­lo­cked se­mi­con­duc­tor laser”, Elec­tro­nics Let­ters, Vo­lu­me: 49 , Issue: 13 (2013)
  • [3] J. C. Bal­zer, T. Schlauch, A. Klehr, G. Er­bert, M. R. Hof­mann, “All se­mi­con­duc­tor high power fs laser sys­tem with va­ria­ble re­pe­ti­ti­on rate”, SPIE 8277, Novel In-Pla­ne Se­mi­con­duc­tor La­sers XI, 827713 (2012)
  • [4] J. C. Bal­zer, T. Schlauch, T. Hoff­mann, A. Klehr, G. Er­bert, M. R. Hof­mann, “Mo­de­lo­cked se­mi­con­duc­tor laser sys­tem with pulse pi­cking for va­ria­ble re­pe­ti­ti­on rate”, Elec­tro­nics Let­ters, Vo­lu­me: 47, Issue: 25 (2011)
  • [5] T. Schlauch, J. C. Bal­zer, A. Klehr, G. Er­bert, G. Tränk­le, and M. R. Hof­mann, “Fem­to­se­cond pas­si­ve­ly mo­de­lo­cked diode laser with in­tra­ca­vi­ty dis­per­si­on ma­nage­ment”, Op­tics Ex­press Vol. 18, Issue 23, pp. 24316-24324 (2010)


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Ruhr-University Bochum
Faculty of Electrical Engineering
and Information Technology
Photonics and Terahertz Technology
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Prof. Dr.-Ing. Martin Hofmann
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