Tsunami - Beckman Institute Laser Resource Center

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Tsunami The modulation frequency 2wmL must be precisely matched to the repetition rate of output pulses which is C/2L. The rf signal used to drive the - - AOM is, thus, usually generated by a temperature-stabilized crystal oscillator, and the cavity length of the laser is adjusted to obtain the appropriate frequency. The duration of the mode-locked pulses depends on several factors including the gain bandwidth of the laser and the modulation depth of the AOM. Laser media with greater gain bandwidth have the capability of generating shorter pulses. Consequently, active mode locking a Nd:YAG laser produces pulse widths of 30 to 150 ps, while for an ion laser, durations are usually 120 to 200 ps. In passively mode-locked systems, the pulse itself generates the periodic modulation. This can be accomplished with a saturable absorber dye that responds to the instantaneous light intensity in a nonlinear manner. At low light intensity the dye is opaque, but at higher intensities the dye is bleached and becomes transparent. The bleaching time of the dye is the effective time of the optical shutter. In the 1980's, a colliding pulse geometry was used with the passive mode locking technique to produce a colliding pulse modelocked (CPM) dye laser. When intracavity GVD compensation (described laser in this chapter) was used with a CPM laser, sub-100 fs pulses were generated for the first time. Also, during the 198OYs, several new developments in broad bandwidth, solid-state laser materials occurred. The most notable of these was titanium-doped sapphire which allowed lasers to be tuned over a continu- - ous range from < 700 to 1100 nm. In 1989, Spectra-Physics was the first company to offer a commercial cw Ti:sapphire laser. The broad bandwidth and good thermal properties of this new material motivated several new mode locking approaches. Additive pulse mode locking (APM) used an interferometrically-coupled, external nonlinear fiber cavity to induce mode locking. In 1991, self-mode locking in Tisapphire was observed to be induced through the intensity-dependent, nonlinear refractive index of the laser medium. At Spectra-Physics Lasers we developed the Tsunami laser, a commercial, mode-locked Ti:sapphire laser based upon a regeneratively initiated technique. Regenerative Mode Locking in Tsunami Like active mode locking, regenerative mode locking in the Tsunami laser employs an AOM within the cavity to generate a periodic loss. However, unlike active mode locking, the rf drive signal used to drive the AOM is derived directly from the laser cavity (Figure A-4). This removes one of the greatest drawbacks of active mode locking, i.e., the requirement that the cavity length match the external drive frequency. In the Tsunami, if the laser cavity length L changes slightly, the drive signal to the modulator changes accordingly. When the Tsunami is initially aligned, the laser is operating cw with - - oscillations from several longitudinal modes. These are partially phase-
I I 0 I I 1 I )I Ulllllll ill I Mode Locking locked, and mode beating generates a modulation of the laser output at a frequency of CI2,. This mode beating is detected by a photodiode and then amplified. Since this signal is twice the required AOM modulation frequency (aML), it is divided by two, then the phase is adjusted such that the modulator is always at maximum transmission when the pulse is present. Finally, the signal is reamplified and fed to the AOM. Most actively mode-locked systems run on resonance for maximum diffraction efficiency. The AOM in a Tsunami is operated off-resonance with a diffraction efficiency of about 1 %. The output pulse width is not controlled by the AOM diffraction efficiency. Rather, pulse shortening in the Tsunami occurs through a combination of positive GVD and nonlinear effects (self phase modulation) in the Ti:sapphire rod. Ultimately, the output pulse width is controlled by adding net negative GVD to the cavity to balance these effects. (Refer to the following section on GVD.) Tsunami Modulator Driver Amplifier + Divider Phase Adjust Photodiode Amplifier Model 3930 Figure A-4: Configuration of the electronics for a regenerative modelocked laser.
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Tsunami Mode-locked Ti: sapphire La
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Table of Contents ... Preface .....
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Table of Contents . Chapter 6: Alig
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Table of Contents Chapter 10: Optio
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Table of Contents Figure 4-7: Typic
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Table of Contents Figure A-6: The f
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Warning Conventions The following w
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List of Abbreviations Used in this
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Tsunami Figure 1-1: The Tsunami Las
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Chapter 2 Laser Safety DANGER The T
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Laser Safety CA UTlON Use of contro
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1 1 1 Il I 11 I I 1 El l11111II~Ill
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Chapter 3 Laser Description General
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Laser Description growth techniques
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Laser Description - AOM OC n Fast P
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Laser Description 2.4 - 2.2 - 2.0 -
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I IIIIIN III I I 1 I 11111 i~ I I I
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I II li I I I i 1 il I 1 11 I 1 1 1
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I Laser Description . Outline Dimen
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Tsunami Input Bezel Connections The
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Tsunami Opto-Mechanical Controls Al
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Tsunami Blue Knob: Vertical Adjust
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~lpl~ f \ Tsunami Opto-Mechanical C
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Tsunami Figure 4-7: 'Qpical MONITOR
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Tsunami r @ Spectra-Physics - - 4 2
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Tsunami Laser Installation Installi
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Tsunami Setting up the Routing Mirr
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Tsunami Aligning the Tsunami Laser
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Tsunami A -----------. PHOTODIODE O
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Tsunami Removing the Purge Line fro
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Tsunami Motorized Mount "Dm-shaped
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Tsunami I I J3 3930 - - - #,-,I --J
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Tsunami CA UTION DO NOT remove or a
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Tsunami Refer to the tables at the
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Tsunami b. Move the stage by hand a
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Tsunami There will be one or two re
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Tsunami Figure 6-9: The Slit Contro
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Tsunami b. Place a white card with
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Tsunami Aligning the Photodiode PC
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Tsunami To measure pulses, use a Sp
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Tsunami pulses, adjust the coarse c
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Tsunami Selecting, Installing, and
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Tsunami Unless you are certain the
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Tsunami Prism Translation Adjust Fi
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Tsunami i. Route the GTI heater cab
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Tsunami Figure 6-18: Pr1/Pr4 prisms
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Tsunami Converting Between fs and p
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Tsunami b. Using an ir viewer, adju
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Tsunami g. Open the shutter. 15. Al
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Tsunami 10. Move Prl and Pr4 into t
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Tsunami 21. Mode lock Tsunami. Refe
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I " n 3 1 ' ! ' I . I 8 8 8 " t 8 0
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Tsunami recommend using 99.999% pur
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Tsunami Mode Locking the Laser 6. W
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Tsunami - - - 710 nrn - - 790 nrn -
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4 Tsunami Beam % 2 mm (0.08 in.) Pr
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Tsunami Table 7-1: Bi-fi Selection
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I I1 ! I : I I I ill 8 I !Il! I1I l
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Lok-to-Clock Electronics LEVEL cont
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Lok-to-Clock Electronics AOM M5f-4
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Lok-to-Clock Electronics Installing
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I I1 I i l l I iil 111 ,111 Ill ,il
Page 133 and 134: P Lok-to-Clock Electronics Model 20
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Page 137 and 138: Lok-to-Clock Electronics Figure 8-9
Page 139: I I1 I l I 1 bll Lok-to-Clock Elect
Page 142 and 143: Tsunami "Clean" is a relative descr
Page 144 and 145: Tsunami Figure 9-1: Drop and Drag M
Page 146 and 147: Tsunami With the exception of pump
Page 148 and 149: Tsunami On rare occasions, the lowe
Page 150 and 151: Tsunami 8. Open the pump laser shut
Page 152 and 153: Tsunami 7. Remove the screws (4) ho
Page 154 and 155: Tsunami DryJClean Flow Adjust Nitro
Page 156 and 157: Tsunami diode such as the Model 393
Page 158 and 159: €968-PEP0 ES68-PEP0 PS68-PEP0 ES6
Page 160 and 161: Tsunami Check marks indicate which
Page 162 and 163: Tsunami Table 10-11: GTI and Bi-Pi
Page 164 and 165: Tsunami Generic Troubleshooting (No
Page 166 and 167: Tsunami Symptom: Laser will not mod
Page 168 and 169: Tsunami Symptom: Unable to mode loc
Page 170 and 171: Tsunami Symptom: Unable to mode loc
Page 172 and 173: Tsunami Symptom: Cannot see individ
Page 174 and 175: Tsunami Symptom: PZT oscillates whe
Page 177 and 178: I I ill ; I l l I I lll.l1 I I I *
Page 179 and 180: I I 111 il I iil i lllill ll I I ll
Page 181 and 182: I I il : I I I 1 I Appendix A Mode
Page 183: Mode Locking is chosen to be the sa
Page 187 and 188: Mode Locking SPM will, thus, broade
Page 189 and 190: Mode Locking The net intracavity GV
Page 191 and 192: Appendix B Pulse Width Measurement
Page 193 and 194: I I 0 I I 1 1 LI I lillll Ill I!,ll
Page 195 and 196: Pulse Width Measurement -% GVD Comp
Page 197 and 198: I I I I I I I I ti 911 I1 I Pulse W
Page 199 and 200: I I I I I I B I IL 1 1 i 1111 I L I
Page 201 and 202: I I 0 I I 1 1 L I I Pulse Width Mea
Page 203 and 204: Appendix C Setting the Line Voltage
Page 205 and 206: Appendix D Material Safetv Data She
Page 207 and 208: Material Safety Data Sheets MATERIA
Page 209 and 210: I I I 1 r $1 I Bill II I I I I Ill
Page 211 and 212: Material Safety Data Sheets MATERIA
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