What is a digital oscilloscope?

　　An oscilloscope is an instrument that displays the shape of a signal in the time domain. It is usually connected with a BNC connector. The digital oscilloscope in the laboratory can be used to detect various electronic signals, such as (1) ion signals of time-of-flight mass spectrometers, (2) pulse voltage to trigger the molecular beampulse valve, (3) photodiode output signal (for measuring laser pulse energy, etc. Taking the two-color multiphoton ionization experiment as an example, the oscilloscope measures the intensity (pulsed energy) of the two lasers and their time difference. So that, we could properly adjust the relative delay time of the two lasers required in the experiment. We can used BNC connector to connect the delay/pulse generator (DG535) to control the time difference between the lasers and the pulsed (high voltage) electric field. Using an oscilloscope to detect these electronic signals can help us accurately and quickly find the experimental conditions we need. The ion signal of the time-of-flight mass spectrometer and the digital signal of the photodiode output signal of the laser intensity are fed into a computer. In this way, we can normalized the ion signal in the recorded vibronic or ion spectra in the REMPI and MATI experiments.
　

How to use a digital oscilloscope?

Taking the model of the laboratory LeCroy LC334A as an example, the important instrument performance specifications are as follows:
---- 500 MHz               Bandwidth
---- 2 GS/s                Single-Shot Sample Rate
---- 10 GS/s              Digitizing Rate for repetitive signals
---- 96 MHz              Power PC^TM 603e Microprocessor
---- 8 million point     Combined Acquisition Memory
---- 2 M points          Acquisition Memory per channel
---- 8-64 MB             System RAM
---- 9-inch (170mm X 125mm) Color Display area, 10-inch CRT
---- Analog Persistence^TM    analog speed and digital flexibility 
---- Full Screen             expand the waveform to fill the entire screen
---- SMARTMemory       　 System Management
---- SMART Trigger^TM       Acquisition, including Exclusion Trigger
---- 170 MB                Portable Hard Disk option
---- ProBus^TM               intelligent Probe System
---- Internal Graphics Print   optional

When actually detecting electronic signals, first connect the instrument to be measured to one of the four channels (such as channel 1) with a BNC connector, and select the channel of the connected signal (such as channel 1) on the channels trace on/off on the panel ). There is an auto setup button on the far right of the panel. Press the auto setup button lightly, and the system will automatically select the more suitable Time/DIV and VOLTs/DIV conditions to capture the electronic pulse signal (such as the laser light intensity signal) you input. If the waveform of the electronic pulse signal you input is not properly displayed on the panel screen, you can adjust the time setting (Time/DIV) and voltage setting (VOLTs/DIV) so that the waveform is properly displayed on the screen. Take the photodiode output signal for measuring the laser intensity as an example, usually the time setting (Time/DIV) is 10ns, the voltage setting (VOLTs/DIV) is between 0.1~1V, press the button in the TimeBase+Trigger area, there is a Row of buttons auto, normal, single, where auto: automatic mode, that is, all triggered and untriggered signals will be displayed, and those that meet the trigger signal can be displayed on the screen stably, and those that do not match will drift left and right. "normal": normal mode, only the signal that meets the trigger can be displayed on the screen, and there will be no left and right drift. "single": single-click mode, only one signal that meets the trigger will be displayed, and the capture will stop immediately. In many cases, the signal waveform on the screen will drift left and right (auto). At this time, just press the normal button to stabilize the measured signal waveform.

Common settings when using a digital oscilloscope in this laboratory (take the photodiode output signal for measuring laser intensity as an example): 

External trigger: Connect the output port of the delay/pulse generator (DG535) with a BNC connector to the external trigger port of the digital oscilloscope, and select external triggering.  

Input: From the photodiode output terminal with BNC connector, set the discrimination level, sampling time, bin width, number of channel, etc.

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