2D-setup manual

by : Jan Hidding (june 2018)
original file in pdf format

Turn on system

• Interlock on
• Turn on laptop hurricane (com port: 2)
• Turn on SDG-II (backside)
• Turn on oscilloscope
• Big chiller
• Amplifier (knob then key)
• Fan (under table)
• Dazzler (backside)
• Laptop dazzler
• Power supply for diodes
• Lockins
• Turn on PC
• Spectra-Physics box: Wait until “TEMP” stops blinking. Then Laser on/off (keep pressed until laser starts)
• Laptop hurricane: ON/OFF (keep pressed for few seconds, wait for laser to warm up)
• Laptop hurricane: Shutter (keep pressed until red box lights up)
• After warming up is complete: ON/OFF (keep pressed until “Emission”)
• Wait for power to ramp up (“pulsing” indicator should go on)
• Reset on SDG-II
• Wait for hour to let laser warm up

Align everything to increase output power and get peak position of spectrum at 590 nm (16950 cm-1)

• Use beam splitter BS1 to align beam in to NOPA. Look at spectrum from OCEAN to see if signal is increasing in power
• To improve temporal overlap of blue and white light in BBO crystal, change translation stage TS1. SENSITIVE! Translation stage can be used to get peak position at 590/595 nm
• Improve spatial overlap of the two beams by changing the direction of blue light with M2 or M3
• Align white light ONLY slightly with PM0 into BBO crystal
• If profile of white light is off (spatially chirped), change the knobs of the sapphire crystal (SC) to improve the white light beam profile
• Changing upper knob of BBO crystal (creating broad spectrum) may also improve signal
• Changing 2nd harmonic creating BBO crystal (BBO2) may also improve signal slightly
• Power can be increase with focus of negative lens (NL1) in the telescope configuration. This will deteriorate beam profile (good profile is more important than higher power)
• If beam profile is off, try changing sapphire crystal slightly to get a round homogenous spot

Align probe and pump through pinholes and into spectrometer

• If everything is aligned, one should be able to align probe and pump through pinholes PH2 and PH5 with the parabolic mirror PM1. If not, probe has priority
• Pump is aligned through PH1 & PH2 using M3 and M4 respectively
• Probe is aligned through PH3, PH4, PH5 & PH6 using BS2 and M5. Good alignment with PH4 is important as delay stage needs to be well aligned. Another removable pinhole PH6 should be used on the other side of the board to align probe in to spectrometer

click for larger

Alignment after board into spectrometer

• To see spectrum on PC: “Extras” -> “Show continuous”
• Check whether probe goes through PH7/8/9/10 and in to spectrometer (without cuvette and pinhole intensity on PC should be around 0.3)
• When misaligned, slightly change PM2 to get in through PH7 and PH8 and PM3 to get it through PH9
• Use M7 and M8 to align through PH10 and increase signal strength. Also use these mirrors to remove any strange fringes in the spectrum
• Lastly change the lens L2 to increase signal

Align pump and probe through 50 μm pinhole

• Block pump beam and align 50 μm pinhole with probe beam (Therefore, only use the stages that translate the pinhole orthogonal to the beam. Do not change the focus position.)
• Block probe beam and align pump beam into pinhole using M6
• Make sure that PH7 is blocking pump and not probe pulse
• Install cuvette and align with pinhole. Use level to position cuvette horizontally
• Block pump and get back reflection of probe on to pump to get a small angle relative to probe
• Clear and measure baselines
  - Dim lights and block probe and pump
  - “Extra” -> ”Clear baselines”
  - “Extra" -> ”Measure baselines” (10000 pulses)

click for larger

Pump probe to determine time zero (t0) and check if everything is in order

• Set power pump & probe to 200nW (dim roomlight!, take pulse repetition rate into account to set the proper pulse energy, because ΔE=Pavg/f)
  - 500Hz 100nW
  - 1000Hz 200nW
• Use dazzler to chop the pump pulse (fpump=500 Hz, fprobe=1000 Hz) by putting dazzler to A/B mode -> “Load”
• Check if polarization of probe and flow direction are correct
• PC: “Scan” “Select input” -> check:
  “VisArray…1.ClockedInput1D_1” & “VisArray…1.ClockedPumpProbeInput1D_1”
• Roughly determine t0 by scanning large range with large step size “Scan” -> "Scan"
  - Scan motor: PIDelay_1 
  - Start position: -5000 fs
  - End position: 5000 fso Delta position: 20 fs (better use 20 fs here. Otherwise your time zero is ±200fs)
• Obtain t0 by fitting integrated signal with XYY
• Move stage to t0: “Motors” -> “Move motor(s)…” -> PIDelay_1=t0
• “Scan” -> “Multi-delta scan…”
  - Scan Motor: PIDelay_1
  - Delay#1 : 1, NrAverages: 10, Make bidirectional scan
  - Start -1000 (delta 200), -200 (delta 20), 1000 (delta 100), 5000 (delta 200), End 30000

2D measurement

• Put Dazzler back to A mode and to “zero”
• Check power of pump and probe (to be sure)
• PC: 2DFT Dazzler -> Settings:
  - Nr averages=250
  - Max delay (fs)=300/400
  - Delta delay=0.6
  - Nr Phase states=2 : Multiplier phase 1=1, Multiplier phase 2=-1
  - Save single scans: None
  - Mark “Crop the X-axis to the spectrum”
• To determine whether there is a lot of scattering from the pump, one can block the probe and run a short scan to see whether there is diagonal signal due to scattering:
  - 2DFT -> Scan
• For real measurement: 2DFT -> Dual loop scan -> Single loop:
  - Start position: 0 fs
  - End position: 1000 fs
  - Delta: 100 fs

Microscope filters

Dichroic mirrors : 25x36x1 mm
Emission filter : 25 mm round with ring
Currently installed :
[ Measured at ~45 degrees in absorbtion spectrometer. X-axis=wavelength, y-axis=absorbance. This should be similar to reflection ]

1. [red curve] ?
2. [green curve] used by Artur: Dichroic ?, emission : ET425LP
3. [blue curve] dichroic probably T525lpxr, emission : HQ595/20M

Frequency doubler / tripler

• Remove first dichroic beamsplitter for switching between doubling and tripling [left # 6, 2 screws]
• Red filter on output blocks fundamental (or doubled ?)
• Rotate axis of second crystal is test for really tripling the light
• Time overlap fundamental and doubled is very critical
• To focus the light in the second crystal, use the horizontal knob
• Overlap fundamental and 2 nd harmonic use second mirror 14
• Fundamental and doubled are co-linear
• To make better collinear : beamwalking of 2x mirror 14
• Top : tripled, bottom doubled.
• Instead of red filter, use UG11 with tape on the top hole, to block the doubled light
• SHG crystal is now 3 mm, instead of original 1.5 mm. Fast times are not very important.

Both doubler and tripler tuning knob : clockwise to higher wavelength.

2nd crystal (BBO) is now 2 mm.

Verdi : 4.5 W
810 nm → 405 nm, 2 MHz : 0.55 mW

Verdi : 5 W
885 nm → 295 nm, 2 MHz : 28 micro watt

13-7-2015
Verdi 5W, humidity : 33%
895 nm, monitor 129 (modelocked) : 26 microwatt doubled
907 nm, monitor 122 (modelocked) : 3.6 microwatt tripled
909 nm, monitor 118 (modelocked) : 2.6 microwatt tripled
911 nm, monitor 108 (modelocked) : 0.8 microwatt tripled

21-9-2015
Verdi 5W, humidity 34%, 911 nm, monitor 109 (modelocked) : 7 microwatt tripled.
Ben helped :
- FdH : also used the fine tuning of the Mira : this helped a bit.
- In pulse picker : adjusted height helped a bit.
- First #14 mirror tweaked = overlap Fund. & SHG : this helped.
- Better time overlap : it looked that the time overlap got stuck. Maybe the delay stage is dirty & stuck. Try push.
- Whilelooking at the THG power, change prism of mira a bit : this can make the pulse shorter.

10-11-2015
Verdi 5W, humidity 34%, 811 nm, monitor
Doubled output 0.36 mW (2MHz) Should be more ?

Bypass pulse picker

After the end mirror of the pulse picker, 2 spots can be seen : a bright spot, which is blocked, and a faint spot, which is transmitted. The faint spot are the pulse-picked pulses.

Insert an 3/32 allen key in the top screw of the endmirror, at 8 o'clock position. By turning it clockwise to the 4 hour position, both spots are moved upwards, and the unpicked pulse now falls on the mirror in the doubler (M2 right).
In order to be completely unblocked, the unperturbed beam fell a little higher on mirror M2 then the picked one.

Realignment doubler

Use M2 (right) and M2 (left) to steer the beam correctly in the crystal. NB : changing the pulse picker output angle, M2, M2 etc. etc has immediately effect on the needed angle of the crystal.
NB : while aligning, the Mira sometimes dropped out of mode-locking : maybe some light bounced back. A slightly different alignment of the 2 M2 mirrors seemed to help. It also helps to close the Mira slit a bit more, to make the mode-locking more stable.

Final alignment : use right M2 to put the beam at the correct height on the left M2 mirror. Align the left M2 mirror, so the doubled beam is at the correct height a few meters away from the doubler.
Only the 2 M2 mirrors are used!

The original heights are (for the pulse picked beam) :
M2 (right) : 7.8 cm (slightly below middle)
M2 (left) : 8.1 cm (slightly above middle)
M3 (before crystal) : at the lower part of the mirror
M6 (left) : blue light at 5.4 cm
Far field : blue light at 13.0 cm

The heights for bypassing the pulse picker are :
M2 (right) : 8.1 cm
M2 (left) : 7.8 cm

5-2-2016
800 nm, 4.5 W, 18.85 A, Baseplate 22.69 C, RH 25%, Monitor 142 (ML)
With pulse picker : 0.34 mW at 400 nm.
Bypassed pulse picker : 22 mW at 400 nm (= 64 x more, should have been 40 x !)

Pulse picker

The output of the pulse picker consists of 2 dots. The upper one is the picked pulse, the lower one is the 90 MHz train.

Normally, the picked pulse is transmitted into the frequency doubler, and the 76 MHz train is blocked inside the pulse picker. It is possible to adjust the height of the thing at the exit of the pulse picker which blocks the 76 MHz train.

To ‘pseudo’ bypass the pulse picker, adjust the vertical position of mirror 2 (the one after the light passed the crystal ), so the 76 MHz beam moves up (over the blocker) and enters the frequency doubler. The pulse picker can be switched off completely somewhere at the back of the control box

• Optimize with power meter on the double or so result
• height of the beam through crystal : the lower and closer to the transducer the more efficient pulse picking. Too low, the beam gets clipped. Use an IR viewer to watch the area just before the crystal.

NB : changing the height of the crystal also changes the timing : it takes longer before the acoustic wave hits the laser beam

• Timing on the control box : coarse : don’t use, fine : use.
• Power to the transducer.
• Side knob : height of the crystal. You see if you move it on, it will go through several maxima. The best one should be the lowest (in position), without clipping. This height knob is an alternative to the timing on the controller.
• 2 top knobs : angle of crystal : both are needed !!
• Other side knob : focus (not so important).
• Pulse picker bragg angle is wavelength dependend !

Cleaning of the crystal

Very carefully. Use methanol (never acetone, dissolves the glue).
Use just a lens paper with a drop of methanol. Don’t use hemostat.

Opening the pulse picker

Push the little buttons at the sides inwards (have little levers on the inside), but make sure not to push the side plates themselves inwards.

Pulse picking frequency

Works with a divider on the control box. Max frequency is 2 MHz.
So divider on 20 → 1.9 MHz.

Menu alignment

Pulse picker runs in auto-run mode : easier for aligning

Numbers on display

1 65 106
100 80
20
[don't know if originally the 1 was really 1]

Verdi 5W @812 nm : Mira about 450 mW output. Measured with power meter and attenuator.
Pulse picker output about 7 mW. Efficiency = 60%. (According to Maxim, should be 90 %)

Streak Camera : Error corrections

Streak camera sensitivity along the time axis

The streak camera was used to measure cw (continuous)light, in this case a white LED.
Since this light has no time dependence, it should have the same height, at all timevalues.

The following data was measured with Synchroscan timebase 4 (30000×56 ms exposures, monochromater slit 10 micron, streak camera slit 20 micron).

[ file: : D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-02-25 LED TB1-4\timebase4.txt.
Download raw data:  led_tb1-4.zip ]

If this data is integrated over all frequencies (x-axis), is normalized so the center has height 1, and is displayed as a function of time (red, in ps):

[ file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-02-25 LED TB1-4\Analysis\timebase4 fit.txt ]

It is not a straight line, as it should be, but somewhat quadratic. The blue line is a 2nd degree polynomial fit. A 4th degree is even slightly better.

Possibly, the time sweep is not linear : maybe it is slower at the beginning and the end, and would then accumulate more photons.
To test this, a series of exposures was made with the light of the Mira, going through 2 (roughly) 50% reflecting, parallel mirrors, separated by 22.2 (+/- 0.1) mm. This produces a pulse, followed by a second pulse (about 5 times smaller), delayed by 148 ps (and even an entire weaker and weaker pulse train). By using different delay settings of the streak camera, this pulse pair was measured at 9 different positions on the time axis. At each position, the pulses where fitted, and the time delay between the 2 was determined. If the time-axis of the streak camera is non-linear, these time-delays should appear different at different position on the time axis.

[file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-03-07 Linearity Timebase 4\Analysis\DeltaT vs T.txt]

The y-values are the time difference between the 2 pulses. The x-values are the center-time of the 2 pulses. There is some difference between the delay of the time pulses. But it looks like this non-linearity is not enough to explain the quadratic behavior.

It is unknown what the reason is. It looks like the ‘sensitivity’ of the streak camera is time dependent, although this does not make much sense.

But, as a first order approximation, one could simply divide the streak camera data by the quadratic blue line (see MatrixCalc, tab ‘Streak’,’ Correct Z along time’ );

In the following graph, the ‘sensitivity’ deviation is show for all 4 synchroscan timebases. (1: yellow, 2:green, 3:blue, 4:red) (using a 2nd degree polynomial fit)

[file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-02-25 LED TB1-4\Analysis\timebase1-4.txt]

To compare them, the time-axis (x-axis) is normalized to 1. Basically, only timebase 3 and 4 deviate significantly.

In the following graph, the ‘sensitivity’ deviation is show for 4 single sweep timebases. (5ns : red, 10 ns : green, 20 ns : blue, 50 ns : orange) (using a 2nd degree polynomial fit)

[file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-03-01 LED SingleSweep\Analysis\SingleSweep 5-50ns sensitivities compared.txt]

The error in the green and blue curve is estimated to be 10%; So if needed, a better measurement has to be done.

Streak camera image tilt/shift

Using Synchroscan timebase 4, also the calibration lamp was used as a CW light source (2nd image is the line at 425 nm)

[ file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-02-24 Calibration lamp TB4\3.img ]

The lines seem to be sligthtly tilted or shifted. One explanation might be that the CCD camera to record the image is slightly rotated. The positions of the maximum of the line at 425 nm were determined as a function of time :

[ file: D:\Lab documentation\5117.-109 Streak camera\Anomaly correction measurements\2016-02-24 Calibration lamp TB4\Analysis\Positions img3 425 nm as pixelnrs .txt ]

The x-axis is now the array-element number along the time axis. The y-axis is the array-element number along the frequency axis.
The green line is the position of the maxima. . It is not a flat line, as it should be.
The red line is a fit with a 1st degree polynomial, the blue line a 2nd degree polynomial.
The fact that a 2nd degree polynomial fits clearly better, seems to rule out the explanation that the CCD camera is simply rotated.
But, as a first order approximation (using the 1st degree polynomial), one could assume the image IS rotated, and then correct it, by rotating the image by -0.432 degree CCW from the x-axis (see MatrixCalc, tab ‘Streak’, ‘Rotate (deg)’).

2. Using the same method to fit the LED data of SynchroScan Timebase 1-4 with 2 gaussians yields :

(average angle = -0.417)

NB: for all 4 datas : a 2nd degree polynomial fits better !

Using the same method to fit the LED data of SingleSweep 5-50nswith 2 gaussians yields :

NB: for all datas : a 2nd degree polynomial fits better !

It might be that it’s not the CCD camera which is slightly rotated, but e.g. the sweep electrodes are slightly non-uniform, so the electrons are not swept perfectly vertical (in time), but slightly deviated.

Streak Camera : Triggering

The photodiode

A little bit of the light of the Mira, is reflected with a transparent pellicle to the C1808-03 photodiode. [ a spare pellicle is in the cupboard. Thorlabs BP108].

It look like the pellicle works as an interference filter, so the reflection is lower at certain wavelengths.
Here is a graph of the percentage reflection (P-polarization. The laser is horizontally polarized) :

The green light at the side of the streak camera indicates if it gets triggered. If it is not on (and the mira is modelocked), open the variable OD-filter, or put the HP amplifier to 40 dB.

If there is too much trigger signal, it is also not good.
According to manual : “Instruction manual for universal streak camera C5680” , near end :
Light on photodiode : 500 micro-W = 5 mW @ 800 nm : output level : 1.5 V p-p in 50 Ohm

Single sweep

The Single sweep unit uses the trigger signal of the photodiode, but also a signal of the pulse picker. In the C4792-01 menu, the Trig.Mode should be set to Dump Mode !! Otherwise the green trigger light on the side of the streak camera just blinks once a second.

Display on scope

If the signal of the photodiode should be placed on the oscilloscope, then before disconnecting the coax from the photodiode, first the bias power should be turned off.

Streak Camera : Entrance slit

The 0 position of the micrometer is exact. 'Just' closed, is exact at 0.

The first 1 mm of the micrometer is very 'fine' 1-5 mm is 'course'.
This also is shown by the horizontal lines on the fixed part of the micrometer.
The lines for the first mm are spaced further apart then the lines 1-5 mm.

Focus mode : 0-5 mm
Streak mode : 5-30 micron (according to manual) (Ben : 20 micron)
Streak mode, faint light : 30-100 micron (acording to manual)

The slider above the slit-micrometer should be no larger the the width of the photocathode (according manual).

If there are any vertical stripes on the spectrum, it is possible that there is a dust particle on the slit : Instead of going from 0→ 20 micrometer, open it much more, and then go back to 20 micrometer.