AMOS-Streak Camera

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The purpose of these instructions is to give you a quick overview on how to work with the devices. You should still be familiar with the manual and receive a proper introduction from the lab leader or the principal users.

500px|thumb|right|LASER Lab

Device location: Optiklabor F&E4-3GP

Lab location: Building 310 Basement Room no. 054

Phone number: 24669

Lab leader: Ian Howard

Principal users: Andrey Turshatov, Dmitry Busko, Michael Adams, Michael Oldenburg, Vu-Hong Le, Nicolo Baroni

Access: The setup is in a class IV laser lab. Only trained users with key may use the setup. The Lab is located in the basement of building 310. Open the door of the basement of B310, go straight ahead and open another door. The new LASER Lab can be found on your left side.

Short Description

200px|thumb|left|Streak camera with Synchroscan Unit

200px|thumb|right|Streak camera with Slow Single Sweep Unit

The streak camera is a device to measure ultra-fast light phenomena and delivers intensity vs. time vs. wavelength information. It can be used in two configurations:

Synchroscan (< 5 ns)

In this configuration, the streak camera is synchronized with the LASER pulses. i.e., the capacitor in the streak camera charges and discharges in the LASER frequency. This is particularly useful for fast decays. For using this configuration the streak camera set-up has to be loaded with the synchroscan unit. An additional delay unit can be used with the synchroscan to account for the delay between the generation and reception of a LASER pulse and for accurately finding the zero point in time from which decay starts.

Slow Single Sweep

In this configuration, the streak camera is synchronized with the output of a pulse picker which will either divide the LASER pulse frequency by a factor or work in gated mode using the signal generated by an external function generator. For using this configuration, the streak camera set-up has to be loaded with the slow single sweep unit.(See image on right). This is particularly useful for long lived species(> 100 microseconds) with weak intensity of emission. The streak camera then gives the signal accumulated over time.

Start-up Procedure and Measurement

Mounting the Sample

150px|thumb|right|Sample Holder

  1. Choose the required type of sample holder
  2. Fix the sample holder in the marked position on the optical table
  3. Carefully place the sample in the sample holder.
  4. Make sure that the sample is facing the right direction so that it will be incident by the LASER beam and the emission from the sample will reach the entrance slit of the streak camera.
  5. Horizontal and vertical adjustments can be made using the stage on which the chamber is mounted.
  6. If vacuum is required, close the holder with the aid of rubber bushes and clamps such that it is air tight and turn ON the vacuum pump by following the procedure below.


Turning ON the vacuum pump

  1. Connect the inlet tube of the vacuum pump to the sample holder
  2. Make sure that all joints are tightly closed.
  3. Ensure that the ventilation valve is closed. It can be found on the backside of the pump. See image.
  4. Press the green switch and the power button
  5. The display can be changed to different pages by pressing the right/left arrow keys on the pump
  6. Pressure is displayed on Page 340 and the Speed in displayed in terms of rotational frequency in page 309
  7. Wait till sufficient vacuum is generated, normally 10^-5 hPa pressure
  8. If sufficient vacuum is not building up, try moving the ballast valve to remove any residues. It can be seen from the right side of the pump. See image.
  9. If the sample has to be taken out of the chamber, for inspecting or for changing the direction, then first the vacuum has to broken.
  10. For this press the power button. Wait till the speed is below 100Hz. Then open the ventilation valve for faster shut down of the vacuum.
  11. Now, the chamber can be opened and the sample can be taken out for making the necessary changes.
  12. Repeat the procedure for starting the vacuum after tightly securing all joints.
  • Vacuum Pump Gallery
  • Datei:Vacuum pump.jpg

    Vacuum Pump for generating vacuum upto 10^-5 hPa

  • Datei:BallastValve vacuumPump.jpg

    Ballast valve for cleaning out the residues in the Vacuum pump

  • Datei:VentilationValve VacuumPump.jpg

    Ventilation Valve for the Vacuum Pump


Turning the LASER ON

  1. Turn ON the touch screen display for controlling the output of the CHAMELEON COMPACT OPO-VIS System with Idler(if it is not already ON). A mouse is also provided for convenience. Open the software for the OPO Compact system.
  2. It has options for different types of output. The direct LASER output, its SHG, the OPO output and its SHG
  3. Ensure that the shutter is closed and the cooling units for the LASER are switched ON.
  4. Make sure that the LASER will not go beyond or create unnecessary reflections outside the operating plane of the optical table.
  5. Roughly plan the path to be followed on the optical table and place mirrors, lenses and irises accordingly.
  6. Set the required wavelength for the Ti:Sa LASER.
  7. Turn the LASER key to ON position, and wait till the LASER ramps up enough power. Ideally at 800nm the power should be 4.3W.
  8. To start LASER emission, press the shutter button. (A yellow LED beneath the button indicates that the shutter is open)
  9. For alignment purposes, use reduced power, so pump the OPO by clicking on the controller. Generally for the streak camera reduced power after pumping the OPO will be sufficient. If the emission is too weak, one can stop pumping the OPO by clicking again on the controller.
  10. If a wavelength other than the set wavelength or its second harmonic is required, you can use the OPO for selecting the required wavelength. This can be done by clicking on the plot in the touch screen display and then entering the required wavelength on the pop-up window. Then wait for the OPO to tune to that frequency.
  11. Make sure to wear proper eye protection.
  12. To get the LASER output, click on the type of output required.
  13. To start the emission click Ti:Sa out or if the OPO is used to obtain a different wavelength, click opo out.
  14. Check the emitted light with the help of an appropriate detector card
  • LASER gallery
  • Datei:Datei:TiSa OPO Assembly.jpg

    Ti:Sa LASER and OPO-VUS system with Idler

  • Datei:Tablet for LASER-OPO Assembly.jpg

    Touch screen control for LASER system

  • Datei:LASER control.jpg

    LASER Control


Delivering beam to the sample-synchroscan mode

250px|thumb|right|Front View of Chameleon compact OPO-VIS system with Idler

  1. The LASER beam is to be directly taken to the sample from the output of the OPO-VIS in synchroscan mode
  2. Check how it is set currently. If the LASER beam is set in a way that it passes through the pulse picker, it has to be changed for synchroscan mode. Follow the steps below.
  3. Put a mirror at the output of the OPO-VIS, in front of the selected output, so that the beam will be rotated by 90 degrees.
  4. Rotate the beam by 90 degrees again, so that it falls on another mirror which will rotate it again by 90 degrees and make it pass through the pair of irises fixed on the table.
  5. There will be mirrors already fixed to the table to increase the height of the beam and another mirror which will reflect the beam onto the sample.
  6. For proper alignment, make sure that the beam passes through the irises.
  7. Fine tuning can be done using two pairs of irises and mirrors.
    1. Select the pairs such that an iris and a mirror farther from it, but earlier in the beam path form the pair.
    2. Focus on one pair at a time.
    3. Slightly adjust the mirror vertically or horizontally to make the beam pass through the centre of the iris.
    4. Make sure it passes through the centre by closing the iris.
    5. Repeat the same procedure for the other pair
    6. Continue the same procedure on the pairs alternatively, till the beam passes through the centre of both irises.
  8. Adjust the last mirror before the beam hits the sample and the sample stage, so that the beam hits the sample.

Delivering beam to sample through pulse picker

200px|thumb|right|Function generator for external triggering in gated mode and the Pulse Picker Control system

  1. Check how the beam path is set.
  2. If it is not set in the way that the required output passes through the pulse picker, the current setup has to be changed.
  3. Using two mirrors rotate the beam path such that it enters the pulse picker.
  4. There are two possible configurations-long delay(gated mode) and short delay
  5. In case long delay mode is required,
    1. Connect the AUX OUT port of the function generator to the EXT. TRIGGER of the pulse picker controller.
    2. Connect the MAIN OUT 50 ohm port of the function generator to the input port of the delay generator.
    3. Connect the RF port to the pulse picker
    4. Pump the OPO
    5. Turn ON the function generator, pulse picker controller and the delay generator.
    6. Set the trigger mode to "gate".
    7. Press the button for turning ON RF mode on the pulse picker controller
    8. You will see two spots in ON mode. A bright one corresponding to the 2nd order of diffraction of the crystal inside the pulse picker and and a less intense one corresponding to the first order of diffraction.
    9. The beam causing the dim spot is to be blocked using one of the irises, so that it doesn't reach the sample.
    10. See if there is sufficient contrast between ON and OFF modes of RF using a detector card.
    11. If not, contact an authorized user for help to adjust the pulse picker.
  6. Using three mirrors, rotate and align the beam path such that it enters the irises already fixed on the table.
  7. Fine tune the alignment by following the steps given in the previous section.
  8. Adjust the last mirror before the beam hits the sample and the sample stage, so that the beam hits the sample.

Setting up the Streak Camera

100px|thumb|right|Cooling System for Streak Camera

  1. Ensure there is enough water in the chiller. To turn on the chiller, first press the black switches on both units, and then the display on the top unit shows OFF. Give a long press on the OK button and the display will show the coolant temperature. See image.
  2. Make sure that the slit before the streak camera is set to zero (fully closed). See image.

100px|thumb|right|Micrometer to control the slit-opening of the streak camera

  1. Switch on the computer.
  2. Turn on the streak camera and also the software on the computer by Hamamatsu. In the software, open live video and click auto-scale. A green streak will be visible at the center, this is because the cooling is not yet turned ON in the software. Turn Cooling ON in the palette on the left and you can see the streak vanishing.
  3. Depending on the configuration used, turn on the respective delay unit, pulse picker and make sure that they are properly connected and configured.The different modes are described below.

Synchroscan Mode

100px|thumb|right|Power Supply Units Turn OFF the lights in the lab as the streak camera measurements are sensitive

Single sweep Mode

100px|thumb|right|Delay Generator Turn OFF the lights in the lab as the streak camera measurements are sensitive

Single Sweep Gated Mode

Turn OFF the lights in the lab as the streak camera measurements are sensitive

Measurement

  1. Make sure the alignment is correct and that the correct filters are mounted so that only the light to be measured is entering the streak camera. XXX how? XXX some pictures
  2. Start opening up gap for the photocathode slowly by turning the attached micrometer screw. Make sure this is done very slowly and the gap should ideally not exceed 20mm.
  3. You will be able to see a streak on the live video output. XXX add some screenshots XXX
  4. Set the appropriate timescale, gain and delay(if required) in the control palette.
  5. In the software control palette, change the Streak Camera Mode from 'Focus' to 'Operate'. Click auto-scale in the live video window.
  6. Adjust the timescale, gain and photocathode opening for the optimal measurement.
  7. Set the required integration time and save the image and data.
  8. In case the detected light is very weak, you will have to use photon counting mode and save the image after setting a threshold value for detecting a hit per pixel.

Shutdown Procedure

  1. Make sure you have saved all the data required.
  2. Close the photocathode opening.
  3. Turn OFF the software and the streak camera.
  4. Turn ON the lights
  5. Turn OFF the output of the CHAMELEON COMPACT OPO-VIS using the tablet.
  6. Turn the shutter OFF.
  7. Turn Ti:Sa LASER key to Standby.
  8. Turn OFF the delay generator and pulse picker(if used)
  9. Turn OFF the computer and chiller.



Kategorie:Geräte - Devices Kategorie:Prüfmittel - Measuring Equipment Kategorie:F&E4 Kategorie:AMOS

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