Phto-injector laser chain NEWS

Massimo Petrarca & Marta Divall

History:

1Amp2

Problems(for energy)

1Synch.

Problems(Laser -> Gun)

2Harmonic

ConversionEfficiency &Stability

Major issues inJanuary 2008

When NO Harmonic generation

was performed!

May June 2008 Harmonic generation

Performed with Amp1 only:New Problems discovered!

1Amp1

Problems(Over most of the other problems):

June July 2008Amp1 problems

(pulses train instability , ASE,

parasitic lasing)

2Amp2

Problems(for energy)

2Synch.

Problems(Laser -> Gun)

3Harmonic

ConversionEfficiency &Stability

3-pass Nd:YLF amplifier

2 pass Nd:YLF amplifier

Optical gate (Pockels cell)

PC

24

Drive Beam (PHIN); Probe beam~600ps=<Dt=<DtPC

1.5 GHzNd:YLF

Oscillator +Nd:YLF

Preamplifier1047nm

Micro pulses at 1.5 GHz

~666ps; 10W

400us amplification windowfor AMP1

Macro pulse

200us amplification windowfor AMP2

Macro pulse

UV

Dt Dt

Green

Dt

IR

Laser overview

Pulsepicker

First Amplifier layout

M1

M2

M3

M4

M5

1st pass2nd pass3rd pass

F1 = +1146mmPreamp. beam

58cm54cm

21cm3.5cm 2.5cm

5cm

M6 Nd:Ylf rod

-Final configuration: 3passages trough the rod with F1 to ~ compensate for the beam divergence: X(3rd pass)-X(1st pass)~1.2mm; Y(3rd pass)-Y(1st pass)~1mm . Nominal power ~3KW has been reachedSatisfactory trace pulse stability has been reachedTransverse beam parameters:M2

x~2.38; M2x~1.94

Power Measurements Amp1:

Unamplified ~ 5.6 W@ 50 amps ~ 6.7 W@ 60 amps ~ 7.4 W@ 70 amps ~ 8.1 W@ 80 amps ~ 8.8 W

@ 90 amps ~ 9.7 W ~3.0 KW

Amp2: layout

M12

M11

1st pass2nd pass

F2 = +300mm

M6

Nd:Ylf rod

Pericope+FaradyF3 = -114mm

Amp1 3rd pass.

M7M8

M9M10

94cm

57.5cm 20.5cm

122cm

2.5cm 2.5cm

29.5cm

29.5cm

22cm

75cm

156cm

Tot:48cm

PockelsCell

20cm

25cm26cm

7cm

F4 = +802mmF5 = +402mm14.5cm 7cm

-Present configuration: 2passages trough the rod with F3 and F2 for the matching: “beam size rod size”

Satisfactory trace pulse stability has been achievedPower ~6.3KW has been reached with 90A (Amp1@90A)

Way to Harmonic G. crystal

Amp1 + Amp2 @ 90A

-350 -300 -250 -200 -150 -100 -50 0 50 1000

1

2

3

4

5

6

Amplifiers @ 90A:Power [KW] vs Time [ms]

Amp1 + Am2 @ 90A

Power Measurements Amp1:

Unamplified ~ 5.6 W@ 50 amps ~ 6.7 W@ 60 amps ~ 7.4 W@ 70 amps ~ 8.1 W@ 80 amps ~ 8.8 W

@ 90 amps ~ 9.7 W ~3.0 KW

Power Measurements Amp1 @90A+Amp2 ..:

@ 50 amps ~ 10.0W@ 60 amps ~ 10.5 W@ 70 amps ~ 11.2 W @ 80 amps ~ 11.6 W

@ 90 amps ~ 12.3 W ~6.3 KW

Amp1+Amp2 Harmonic GenerationIR

energy within 2ms gate

GREEN energy within

2ms gate

UVEnergy within

2ms gate

Amp1 @90ampsPC on 2ms

( Best Result )

(4.15-1.33)mJ std=0.06mJ

~1.2 mJStd=0.016mJ

0.398 mJStd=0.012

133.3 nJ in a micro pulse

~44 % efficiency

~34 % efficiency

Amp1+Amp2 @90ampsPC on 2ms

(12.3-4.2)mJ std=0.26mJ

3.23 mJStd=0.07mJ

40% efficiency

0.692 mJStd=0.024

~234 nJ in a micro pulse

22% efficiency

A decrease on the conversion efficiency has been observed when both amplifiers are @90AOptimization of the beam size onto the conversion crystals has to be done; nevertheless the

conversion efficiency is still acceptable yielding a micropulse energy of ~230nJ (nominal 730nJ)Collaboration with Guy Cheymol “CEA”

On site synchronization meas.:

22 JNFJJ measreal

Jreal ~ 634 fs (rms jitter required <1ps)

JNF: jitter noise floor ~ 350 fs Jmeas: 724fs

Lecroy SDA (16GHz, 60GS/s+ NewFocus Photodetector25GHz)After on site investigation,

oscillator cavity perturbations due to thermal effects were

suspected

HighQ expert came and fixed the settings of the

oscillator end-cavity mirror(semiconductor saturable

absorber mirror “SESAM”):50C

Degree

Problem has been fixed

HighQ Jitter behavior (over a day)

Synchronization

0

20

40

60

80

100

120

140

160

180

200

0 3600 7200 10800 14400 18000 21600 25200 28800

Time [sec]

Jit

ter

[fs

]

HighQ company provided the unit to synchronize the laser to the ext. rf master clock (~1.499):“Synch”

From this unit it is possible to monitories the jitter “Laser vs Ext-rf”

Open Issues:Even more difficult (it takes time!!):

• The rod probably has to be changed to improve transverse beam profile (poor quality now!).• Third passage has to installed to extract more energy

and to compensate for thermal effect introduced by Amp1 .

• Lenses system for the matching “rod -beam” size along the 3 passages has to be installed …… …..(optimization of the whole beam line that comes after!!!!!)

• Coupling: “Pumping beam vs Nd:Ylf rod” has to be study (no cylindrical lenses installed now; it could be necessary to replaced those lenses to focus pumping beam into the rod.)• Conversion efficiency studies (saturation, best size onto crystals….)

The end