**4. High repetition rate of ultra-high peak power laser systems**

As it was discussed in Introduction (Section 1.3), the applications of the ultra-high peak power laser pulses required also high repetition rate or the other words high average power laser systems. Limitation of the high peak power laser systems on the repetition rate can be overcome by TD-technology and hence can increase their average power. Making the active medium thin reduces the longitudinal gain, which can be compensated by increasing the concentration of active ions and/or using crystals with higher emission cross-section, and the most promising crystal with required characteristics for these amplifiers is Ti:Sa. However, the attempt to increase the longitudinal gain leads to a dramatic growth of the gain in the transverse direction of the active medium. Therefore, TASE and TPG are strongly dependent on the axial gain and the ratio of the pumped area diameter to the crystal thickness (aspect ratio). For thin Ti:Sa active media, these effects cause significant depletion of the inverted population, and hence limit the extracted energy, the same way as it was detailed discussed in Section 2.

The EDP-technique was suggested to be applied for TD crystals [39] and successfully tested [41] mostly in powerful final stages of ultra-high peak power laser systems with hundreds of TWs to tens of PWs power, which are operating in the saturation regime. The overall gain of the amplifier can be kept as small as ~10–20, since the extraction of energy is a major importance. On the other hand, a large amplifier aperture is required for the high energy level. Therefore, power stages of the said Ti:Sa systems require a crystal size ranging from 5 to 20 cm, contrary to "conventional" TD amplifiers with the aperture of few millimeters where several tens of passes can be done [40]. The reasonable number of passes through the amplifier in this case, is restricted up to 6 due to geometrical complexity and available space. These two requirements form the lower boundary for the small signal gain of 3–5 per pass or the saturated one of 1.5–2.

**Figure 15a** demonstrates dependence of the transverse gain on the crystal aspect ratio for different longitudinal small signal gain values, which correspond consequently to the absorbed pump fluence F of G<sup>l</sup> = 10 – F = 3.8 J/cm<sup>2</sup> , G<sup>l</sup> = 7 – F = 3 J/cm<sup>2</sup> , G<sup>l</sup> = 5 – F = 2.5 J/cm<sup>2</sup> and G<sup>l</sup> = 3.5 – F = 2 J/cm<sup>2</sup> . The maximal possible suppression of transverse gain using a conventional method of the side surface cladding and its combination with the EDP-method correspond two horizontal lines (solid and dashed line in the figure). The side surface cladding with a commonly used liquid absorber is considered in both cases. The conventional method of transverse gain compensation supports the aspect ratio between 2 and 4, as seen from this picture, while the EDP-amplifiers can afford 8–15. That means the latter one can be applied as TD-amplifier and can increase the output energy up to 16 times. The maximum value of aspect ratio can be determined from these calculations taking into account the required output energy and crystal thickness. Then, the small signal gain could be chosen depending on amount of pump passes and the crystal doping that will support the required absorption. For example, EDP is able to afford for the small signal gain of 3.5, the highest aspect ratio 15 with the reasonable amount of signal passes of 4–5. So, the Ti:Sa crystal of 15 cm is required for 10 PW laser (300 J); this corresponds to the crystal thickness of 1 cm and doping according to the chosen pump absorption.

As an example, losses have been calculated in a 20 × 2 mm Ti:Sa crystal pumped with 11 J (532 nm, 100 ns) and seeded by 180 mJ using the method elaborated in Ref. [25] with some modification of the computer model. According to these calculations, TASE loss without EDP (dashed curve in **Figure 15b**) is ~80%, the output energy for an EDP-amplifier is 6 J, while energy loss (solid curve) is ~10–15%. The peak power of the laser can reach 120–400TW if compressor transmission efficiency is 70% and pulse duration is 10–30 fs, while the average

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Proof-of-principle experiment of the operation of a broadband EDP-TD amplifier in a 100 TW CPA laser system was presented in Ref. [41]. The amplifier head was fully characterized, including measurement and modeling of the temperature distribution, dynamics of amplifi-

Test bed was assembled in Max-Born-Institute on the base of commercial CPA laser system amplifier, which produces 100 TW peak power, 28 fs laser pulses at 10 Hz repetition rate. The final cryogenically cooled Ti:Sa amplifier has been replaced in experiments with the EDP-TD room temperature cooled arrangement (**Figure 16**). Ti:Sa crystal with a 35 mm diameter, 3 mm thickness and an absorption coefficient of 2 cm−1 was mounted in the homemade thin disk head module. The active mirror scheme was applied for the amplifier. Rear side of the crystal was HR coated, while the front one was AR coated, for both pump (532 nm) and seed (800 nm) wavelengths. The sides surface of the Ti:Sa crystal was coated by the absorbing material (refraction index of 1.76 at 800 nm), for TASE and TPG suppression. The rear surface of the crystal was actively water cooled to room temperature. Three temporally synchronized lasers, each providing 15 ns, 2 J pulses at 532 nm wavelength

Each of the three pump beams passed through the thin disk twice, one pass includes the reflection from the rear surface of the crystal. The total absorption for double pass of pump was measured to be 85%. The vertically separated pump beams one can see on the side view of the **Figure 16** with the smallest incidence angles, where the pump 2 was omitted. Three passes (mirrors S1-S5) amplified a positively stretched seed of few 100 ps pulse duration

Severe parasitic lasing was generated despite the use of the liquid absorber in the absence of the seed, when the active medium was simultaneously pumped with total absorbed energy 3.4 J by the double passed pump beams 1 and 3. This is clearly visible on the oscillogram of the luminescence (**Figure 17a**) from Ti:Sa crystal. EDP technique was applied to avoid TPG losses, extracting energy from the crystal before the second pass of the pump 3 (~3 J of absorbed energy). After first pass of the pump 3, the second one added 0.4 J to the stored energy delaying about 20 ns after the extraction of 0.5 J by the first seed pass (total amplified energy after the first pass was about 1 J). To avoid another round of parasitic generation, the pump pulse from the pump laser 2 was added between the second and third seed passes (**Figure 17b**), which allowed to reach 2.6 J of the amplified energy when the total absorbed pump was about 5 J. Three passes amplification only and two passes of the pump were required for this seed to achieve almost 50% extraction efficiency (compared with tens of passes of conventional Nd:YAG or Yb:YAG TD amplifiers) due to the much greater emission cross-section and

power is close to 0.6 kW at the repetition rate of 100 Hz.

cation, and wave front of the amplified pulses.

pumped area of 24 mm diameter.

(energy −0.5 J) with a total gain of about 5.

As for conventional amplifiers, the EDP method can be applied in a similar way to thin disks amplifiers [28]. This method allows in optimum conditions to significantly reduce the losses in the crystals with the big aspect ratio, or in thin disk crystals (to 5–15%). The EDP method requires an extended pump-pulse duration ranging from tens to hundreds of nanoseconds, or a train consisting of several delayed shorter pulses. EDP can then be naturally combined with thin disk Ti:Sa amplifiers with regularly doping crystals because a smaller portion of the pump energy can be absorbed in smaller crystal thickness per pass. Choosing the correct distances of the pump and the seed pass shoulders, the multipassing pump can be adjusted for the optimum EDP. We demonstrate further that a new line of the CPA ultra-high intense high average power laser systems can be opened by combination of EDP and TDT with a possibility to be scaled up to tens of a PW peak power and hundred Hz-repetition rate.

**Figure 15.** (a) Dependences of transverse gain on crystal aspect ratios; (b) losses calculated for the 200 TW/100 Hz 6-pass Ti:Sa EDP-power amplifier. Shaded area is the pump pulse.

As an example, losses have been calculated in a 20 × 2 mm Ti:Sa crystal pumped with 11 J (532 nm, 100 ns) and seeded by 180 mJ using the method elaborated in Ref. [25] with some modification of the computer model. According to these calculations, TASE loss without EDP (dashed curve in **Figure 15b**) is ~80%, the output energy for an EDP-amplifier is 6 J, while energy loss (solid curve) is ~10–15%. The peak power of the laser can reach 120–400TW if compressor transmission efficiency is 70% and pulse duration is 10–30 fs, while the average power is close to 0.6 kW at the repetition rate of 100 Hz.

**Figure 15a** demonstrates dependence of the transverse gain on the crystal aspect ratio for different longitudinal small signal gain values, which correspond consequently to the absorbed pump

The maximal possible suppression of transverse gain using a conventional method of the side surface cladding and its combination with the EDP-method correspond two horizontal lines (solid and dashed line in the figure). The side surface cladding with a commonly used liquid absorber is considered in both cases. The conventional method of transverse gain compensation supports the aspect ratio between 2 and 4, as seen from this picture, while the EDP-amplifiers can afford 8–15. That means the latter one can be applied as TD-amplifier and can increase the output energy up to 16 times. The maximum value of aspect ratio can be determined from these calculations taking into account the required output energy and crystal thickness. Then, the small signal gain could be chosen depending on amount of pump passes and the crystal doping that will support the required absorption. For example, EDP is able to afford for the small signal gain of 3.5, the highest aspect ratio 15 with the reasonable amount of signal passes of 4–5. So, the Ti:Sa crystal of 15 cm is required for 10 PW laser (300 J); this corresponds to the crystal thickness

As for conventional amplifiers, the EDP method can be applied in a similar way to thin disks amplifiers [28]. This method allows in optimum conditions to significantly reduce the losses in the crystals with the big aspect ratio, or in thin disk crystals (to 5–15%). The EDP method requires an extended pump-pulse duration ranging from tens to hundreds of nanoseconds, or a train consisting of several delayed shorter pulses. EDP can then be naturally combined with thin disk Ti:Sa amplifiers with regularly doping crystals because a smaller portion of the pump energy can be absorbed in smaller crystal thickness per pass. Choosing the correct distances of the pump and the seed pass shoulders, the multipassing pump can be adjusted for the optimum EDP. We demonstrate further that a new line of the CPA ultra-high intense high average power laser systems can be opened by combination of EDP and TDT with a possibil-

**Figure 15.** (a) Dependences of transverse gain on crystal aspect ratios; (b) losses calculated for the 200 TW/100 Hz 6-pass

Ti:Sa EDP-power amplifier. Shaded area is the pump pulse.

ity to be scaled up to tens of a PW peak power and hundred Hz-repetition rate.

, G<sup>l</sup> = 5 – F = 2.5 J/cm<sup>2</sup>

and G<sup>l</sup> = 3.5 – F = 2 J/cm<sup>2</sup>

.

, G<sup>l</sup> = 7 – F = 3 J/cm<sup>2</sup>

of 1 cm and doping according to the chosen pump absorption.

fluence F of G<sup>l</sup> = 10 – F = 3.8 J/cm<sup>2</sup>

82 High Power Laser Systems

Proof-of-principle experiment of the operation of a broadband EDP-TD amplifier in a 100 TW CPA laser system was presented in Ref. [41]. The amplifier head was fully characterized, including measurement and modeling of the temperature distribution, dynamics of amplification, and wave front of the amplified pulses.

Test bed was assembled in Max-Born-Institute on the base of commercial CPA laser system amplifier, which produces 100 TW peak power, 28 fs laser pulses at 10 Hz repetition rate. The final cryogenically cooled Ti:Sa amplifier has been replaced in experiments with the EDP-TD room temperature cooled arrangement (**Figure 16**). Ti:Sa crystal with a 35 mm diameter, 3 mm thickness and an absorption coefficient of 2 cm−1 was mounted in the homemade thin disk head module. The active mirror scheme was applied for the amplifier. Rear side of the crystal was HR coated, while the front one was AR coated, for both pump (532 nm) and seed (800 nm) wavelengths. The sides surface of the Ti:Sa crystal was coated by the absorbing material (refraction index of 1.76 at 800 nm), for TASE and TPG suppression. The rear surface of the crystal was actively water cooled to room temperature. Three temporally synchronized lasers, each providing 15 ns, 2 J pulses at 532 nm wavelength pumped area of 24 mm diameter.

Each of the three pump beams passed through the thin disk twice, one pass includes the reflection from the rear surface of the crystal. The total absorption for double pass of pump was measured to be 85%. The vertically separated pump beams one can see on the side view of the **Figure 16** with the smallest incidence angles, where the pump 2 was omitted. Three passes (mirrors S1-S5) amplified a positively stretched seed of few 100 ps pulse duration (energy −0.5 J) with a total gain of about 5.

Severe parasitic lasing was generated despite the use of the liquid absorber in the absence of the seed, when the active medium was simultaneously pumped with total absorbed energy 3.4 J by the double passed pump beams 1 and 3. This is clearly visible on the oscillogram of the luminescence (**Figure 17a**) from Ti:Sa crystal. EDP technique was applied to avoid TPG losses, extracting energy from the crystal before the second pass of the pump 3 (~3 J of absorbed energy). After first pass of the pump 3, the second one added 0.4 J to the stored energy delaying about 20 ns after the extraction of 0.5 J by the first seed pass (total amplified energy after the first pass was about 1 J). To avoid another round of parasitic generation, the pump pulse from the pump laser 2 was added between the second and third seed passes (**Figure 17b**), which allowed to reach 2.6 J of the amplified energy when the total absorbed pump was about 5 J. Three passes amplification only and two passes of the pump were required for this seed to achieve almost 50% extraction efficiency (compared with tens of passes of conventional Nd:YAG or Yb:YAG TD amplifiers) due to the much greater emission cross-section and

**Figure 16.** Experimental set up. The layout of the seed amplification consists of mirrors S1–S5 (red lines). The green beams are pump. Mirrors P1-1 and P1-2 were used for pump laser 1, mirrors P2-1 and P2-2 were used for pump 2, mirrors P3-1, P3-2 and P3-3 were used for pump 3.

**Figure 18b** shows the temperature growth dynamic taken at the central point of the crystal until temperature stabilization. As seen from this curvature, the stabilization was reached after the crystal pumping within 20 s with 10 Hz repetition rate of the pump pulses. **Figure 18** shows that a coolant temperature of 18°C was sufficient to keep the maximal crystal temperature after stabilization under 30°C. The variation through the pump area was only 3°C, which does not significantly affect the seed beam wave front. The liquid absorber consumed a TASE absorption which is the largest portion of total luminescence; so, most of the pump energy was transmitted to the crystal heating. That means, similar result could be seen with the same crystal pumped with 8 J at the same repetition rate, when half of this energy is being extracted by the seed. Furthermore, a higher coolant flow speed could reduce significantly

**Figure 18.** (a) Cross section of temperature distribution in the amplifier crystal after heating stabilization during pumping by the 4 J per pulse at 10 Hz repetition rate. The curve shows the temperature distribution of the horizontal mean section of the pumped area (red, solid line) and temperature distribution in the amplifier head (inset); (b) central

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The impact on the beam wave front was also measured during these crystal heating conditions. Measurements were taken until the crystal temperature was stabilized. The wave front before and after pumping was measured and consequently demonstrated P-V: 0.32 μm, RMS: 0.06 μm and after heating stabilization P-V: 1.51 μm RMS: 0.39 μm. These results are better than the comparable single-shot laser systems with side extraction of the heat measured

Heat extraction from the Ti:Sa thin disk was numerically modeled to match experimental conditions and scale-up the system for higher repetition rates of 100 Hz, corresponding to 360 W of the thermal load. These model parameters account for the 8 J pumping with an energy extraction efficiency by amplification of the seed pulses of 50%. Proper cooling conditions were considered using a flow velocity of 5 m/s, and coolant temperature of 5°C. According to these simulations, the temperature profile is much more symmetric and smoother in the thinner crystal than in thick one. For 3 and 2 mm crystals, the temperature difference between the center and the edges was improved with central peak temperatures of 83.5 and 73.5°C, respectively.

highest temperature.

before wave front correction [42].

point temperature growth dynamic of Ti:Sa crystal.

**Figure 17.** Oscillogram of the luminescence from Ti:Sa crystal. (a) Parasitic generation after double pass of the pump beams 1 and 3 with total absorbed energy about 3.4 J; (b) the luminescence with three seed passes.

thickness of the Ti:Sa crystal. The typical near field cross-section of pump and seed amplified after the third pass beams had the flat-top shape with the good uniformity.

The temperature distribution over the crystal input surface in the transverse direction through the crystal was measured (**Figure 18a**) with a thermal imager. The crystal was pumped with 4 J of pulse energy at 10 Hz repetition rate without the energy extraction by the seed. Average flow speed was about 7 cm<sup>3</sup> /s with the initial temperature of the coolant 18°C.

**Figure 18.** (a) Cross section of temperature distribution in the amplifier crystal after heating stabilization during pumping by the 4 J per pulse at 10 Hz repetition rate. The curve shows the temperature distribution of the horizontal mean section of the pumped area (red, solid line) and temperature distribution in the amplifier head (inset); (b) central point temperature growth dynamic of Ti:Sa crystal.

**Figure 18b** shows the temperature growth dynamic taken at the central point of the crystal until temperature stabilization. As seen from this curvature, the stabilization was reached after the crystal pumping within 20 s with 10 Hz repetition rate of the pump pulses. **Figure 18** shows that a coolant temperature of 18°C was sufficient to keep the maximal crystal temperature after stabilization under 30°C. The variation through the pump area was only 3°C, which does not significantly affect the seed beam wave front. The liquid absorber consumed a TASE absorption which is the largest portion of total luminescence; so, most of the pump energy was transmitted to the crystal heating. That means, similar result could be seen with the same crystal pumped with 8 J at the same repetition rate, when half of this energy is being extracted by the seed. Furthermore, a higher coolant flow speed could reduce significantly highest temperature.

The impact on the beam wave front was also measured during these crystal heating conditions. Measurements were taken until the crystal temperature was stabilized. The wave front before and after pumping was measured and consequently demonstrated P-V: 0.32 μm, RMS: 0.06 μm and after heating stabilization P-V: 1.51 μm RMS: 0.39 μm. These results are better than the comparable single-shot laser systems with side extraction of the heat measured before wave front correction [42].

Heat extraction from the Ti:Sa thin disk was numerically modeled to match experimental conditions and scale-up the system for higher repetition rates of 100 Hz, corresponding to 360 W of the thermal load. These model parameters account for the 8 J pumping with an energy extraction efficiency by amplification of the seed pulses of 50%. Proper cooling conditions were considered using a flow velocity of 5 m/s, and coolant temperature of 5°C. According to these simulations, the temperature profile is much more symmetric and smoother in the thinner crystal than in thick one. For 3 and 2 mm crystals, the temperature difference between the center and the edges was improved with central peak temperatures of 83.5 and 73.5°C, respectively.

thickness of the Ti:Sa crystal. The typical near field cross-section of pump and seed amplified

**Figure 17.** Oscillogram of the luminescence from Ti:Sa crystal. (a) Parasitic generation after double pass of the pump

**Figure 16.** Experimental set up. The layout of the seed amplification consists of mirrors S1–S5 (red lines). The green beams are pump. Mirrors P1-1 and P1-2 were used for pump laser 1, mirrors P2-1 and P2-2 were used for pump 2,

The temperature distribution over the crystal input surface in the transverse direction through the crystal was measured (**Figure 18a**) with a thermal imager. The crystal was pumped with 4 J of pulse energy at 10 Hz repetition rate without the energy extraction by the seed. Average

/s with the initial temperature of the coolant 18°C.

after the third pass beams had the flat-top shape with the good uniformity.

beams 1 and 3 with total absorbed energy about 3.4 J; (b) the luminescence with three seed passes.

flow speed was about 7 cm<sup>3</sup>

mirrors P3-1, P3-2 and P3-3 were used for pump 3.

84 High Power Laser Systems

The obtained results demonstrate the capacity to build a room temperature cooled final amplifier, providing few Joules energy of the seed laser pulses with in a 100 s TW/100 s Hz CPA laser systems.

Summarizing this investigation, we can conclude that the replacement of regular thickness Ti:Sa crystals in the booster/final amplifiers of ultra-high pack power laser systems on EDP-TD Ti:Sa amplifiers allows significantly to increase the repetition rates at an average power. These systems could reach such new frontier parameters as 100 s TW/100 s Hz and up to 1 kW output average power, using room temperature cooling systems and existing now pump lasers, which are able to deliver few Joules in green with the same repetition rate. At the same time, there are no limitations for further growing these parameters up to few PW peak power and

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In this chapter, several ideas for innovation of the ultra-high peak power CPA laser systems were presented. Exploiting these ideas, one is able to significantly increase the output energy (up to KJ-level), reduce pulse duration (down to few fs) and so increase output peak power up to 100 s of PW. At the same time, the possibilities of average power growing of these systems

EDP-method for Ti:Sa final amplifiers was revealed as easiest way to reach a very high output energy [25, 27, 28]. EDP amplifier, when operated under the optimal conditions, is capable of significantly increasing the extracted energy and reducing the losses connected with TASE and TPG. With the existing large aperture of Ti:Sa crystals and index-matched liquid absorbers, it is possible to approach the sub-kJ level of extracting energy. With 70% compressor transmission efficiency and 15 fs pulse duration, about 30 PW power level could be reached. The powerfulness of EDPCPA technology was proved by spreading the method in the many world class laboratories and reaching recently the output energy about 200 J and world record peak power of 5 PW. Next steps of the output energy ~ 500–800 J could be done with the exist-

Two recently developed method of pulse shortening have been discussed in the subtitle 3. The ability to obtain a greatly broadened spectral bandwidth in Ti:Sa laser amplifiers was shown using both π- and σ-axis and shaping the spectral gain via engineering the spectral polarization of amplified pulses [34]. Amplification bandwidth exceeding 85 nm at a gain of 200 was demonstrated in a proof-of-principle experiment. These experiments have shown also that active pre-shaping of the pulse spectrum with PE amplification preceding saturated amplification in conventional CPA amplifiers can be successfully used to compensate the spectral red-shifting and gain narrowing that accompany amplification in Ti:Sa CPA systems. The computer modeling revealed that a polarization-encoded chirped pulse amplification scheme can be scaled to higher energies and produce multi-Joule pulses with bandwidth close to

The multiple stage compression method based on spectral broadening using SPM in the bulk of material with the further recompression of the chirped pulse is able to deliver even shorter pulse duration below 10 fs without energy sacrificing [37]. Further development of this idea, with SPM in thin film below 1 mm and much higher intensity (up to tens of TW/cm<sup>2</sup>

) was

100 Hz repetition rate after developing the pump lasers required for that.

**5. Conclusion**

up to 10 s kW was also demonstrated.

ing now Ti:Sa crystals of 20–30 cm diameter.

200 nm, making few-cycle petawatt Ti:Sa systems feasible.

Numerical modeling of scaling larger peak power amplifier modules with double channel cooling and double crystals (three cooling channels) design were also conducted in Ref. [43].

Double channel cooled disks with diameters ranging from 6 to 20 cm and corresponding thicknesses of 0.6 to 2 cm, were investigated (**Figure 19a**). The inlet flow velocity was 4 m/s in all cases to ensure high levels of heat extraction from the disk gain modules. Every gain module would remain under 45°C up to 40 Hz of operation relative to the coolant temperature. When the repetition rate is growing up further, one can see significant rise in the temperature increase (TI), nevertheless, the temperature profile would remain smooth and flat in the region of the laser amplification. Peak power could reach 8.5 PW and an average power 17 kW with compressor efficiency of 60% and pulse duration of 20 fs [**Figure 19a** (inset)]. The maximal repetition rate when amplifiers could operate safely and without serious beam degradation can be estimated based on the obtained TIs. Extremely efficient heat extraction can be obtained by increasing the diameter, while maintaining the aspect ratio of the gain disks with two coolant channels and thus flat temperature profiles with high repetition rate operation.

Further increase of the average power could be achieved by splitting the gain disk to multiple plates with reduced thickness and increasing the number of coolant channels. Four gain modules with double disk sizes ranging from 6 to 20 cm was investigated, with three coolant channel arrangement (**Figure 19b**). These simulations demonstrate 2 kW output average power with a TI in the disks of 21.5°C, and 28 kW average power at TI of 36°C using multiple disks and cooling surfaces with proper coolant flow conditions.

**Figure 19.** (a) Temperature dependence on repetition rates for various single disk sizes. Pump energy 40, 57, 77, 101, 127, 308, 567 J, for the diameters starting from 6 cm respectively. Peak power of compressed pulses listed in inset (compressor efficiency-60%, repetition rate-100 Hz and pulse duration-20 fs); (b) temperature in the single and double disk modules (Ti:Sa crystals of 6, 10, 15 and 20 cm diameters, 100 Hz for all cases) cooled by three channels using 4 m/s flow velocity at the inlet boundary of the channels.

Summarizing this investigation, we can conclude that the replacement of regular thickness Ti:Sa crystals in the booster/final amplifiers of ultra-high pack power laser systems on EDP-TD Ti:Sa amplifiers allows significantly to increase the repetition rates at an average power. These systems could reach such new frontier parameters as 100 s TW/100 s Hz and up to 1 kW output average power, using room temperature cooling systems and existing now pump lasers, which are able to deliver few Joules in green with the same repetition rate. At the same time, there are no limitations for further growing these parameters up to few PW peak power and 100 Hz repetition rate after developing the pump lasers required for that.
