3B Scientific UE4070320 Q-Switching For Nd Yag Laser Trigger Mode Instruction Manual

3B Scientific UE4070320 Q-Switching For Nd Yag Laser Trigger Mode

Specifications

• Model: UE4070320
• Product: Q-Switching for Nd: YAG Laser

Product Information

• Objective: Q-switching circuit for Nd: YAG laser with Cr: YAG module
• Summary: Q-switching of a laser enables short, high-energy pulses by controlling resonator losses.
• This experiment involves implementing a passive Q-switching circuit using a Cr: YAG module and recording laser pulsing over time to calculate pulse energy.
• Warning: Class-4 laser equipment is used to emit infrared light.
• Always wear laser protective goggles and avoid direct exposure to the laser beam.

Required Apparatus

• Laser Diode Driver and Two-Way Temperature Controller Dsc01-2.5 (Item Number: 1008632)
• Optical Bench KL (Item Number: 1008642)
• Diode Laser 1000 mW Nd: YAG Cristal (Item Number: 1009497)
• Passive Q-Switch Laser Mirror I (Item Number: 1008635)
• PIN Photodiode, Fast Filter RG850 (Item Number: 1008637)
• Alignment Laser Diode Transport Case KL (Item Number: 1008638)
• Laser Safety Goggles for Nd: YAG Laser (Item Number: 1008641)
• Digital Multimeter P3340 (Item Number: 1008648)
• Digital Oscilloscope 2×100 MHz (Item Number: 1008634) HF Patch Cord, BNC/4 mm Plug HF Patch Cord (Item Number: 1008651)
• IR Detector Card (Item Number: 1017879)

Product Usage Instructions

1. Ensure all required apparatus is set up correctly and securely.
2. Wear laser safety goggles before starting the experiment.
3. Implement the passive Q-switching circuit using the Cr: YAG module as per experiment guidelines.
4. Record the laser pulsing over time using the digital oscilloscope.
5. Calculate the energy of the pulses from the average power and frequency of repetition.
6. Follow proper safety precautions throughout the experiment.

FAQ

Q: What should I do if I encounter difficulties in implementing the passive Q-switching circuit?

A: If you face challenges during the setup, refer to the user manual for detailed instructions. You can also seek assistance from a qualified technician or contact customer support for further guidance.

Q: How do I ensure the accuracy of calculating pulse energy?

A: To ensure accuracy in calculating pulse energy, make sure to record precise measurements of average power and frequency of pulse repetition. Double-check your calculations and seek assistance if needed to verify the results.

EXPERIMENT PROCEDURE

• Set up and optimize a Q-switching circuit for an Nd: YAG laser using a Cr: YAG module.
• Record the pulses and determine their duration.
• WARNING This experiment involves the operation of class-4 laser equipment which emits light in the (invisible) infra-red part of the spectrum.
• Goggles that protect against laser light should always be worn.
• Even when wearing such goggles, never look at the laser beam directly.

OBJECTIVE

• Q-switching circuit for Nd: YAG laser with Cr: YAG module

SUMMARY

• Q-switching of a laser makes it possible to generate short, high-energy pulses. It works by controlling the laser threshold by increasing or decreasing resonator losses.
• You are to imple-ment a passive Q-switching circuit with the help of a Cr: YAG module and then record the laser pulsing over time.
• The energy of the pulses can be calculated from the average power and the frequency with which they are repeated.

REQUIRED APPARATUS

BASIC PRINCIPLES

• Q-switching (also called giant pulse formation) makes it possible to generate short, high-energy laser pulses, as required in the processing of materials, for example.
• It works by controlling the laser threshold by increasing or decreasing resonator losses.
• When losses are high, it prevents the build-up of oscillation in the resonator and causes pumping energy to be stored in the laser crystal.
• Once the resonator is enabled by reducing the losses, a laser pulse of intensity orders of magnitude greater than the intensity in continuous mode is generated.
• The difference between this and spiking is that the inversion density with Q-switching far exceeds the threshold value.
• A distinction is made between active and passive Q-switching. Passive Q-switches are absorbers in which the capacity to absorb can be modified through the light in the resonator.
• Active switches are typically acousto-optic, electro-optic or mechanical switches, which control the transmission externally.
• The use of an absorbing crystal as a passive Q-switch requires that the absorption can be saturated. That means that its effective absorption cross section must be larger than that for the light from atoms in an excited state, also that the lifetime of the excited level is both longer than the duration of the laser pulse and shorter than the frequency of repetition. A Cr: YAG crystal fulfils all these criteria.
• To fully describe the dynamic response of the passively Q-switched laser, the rate equation for the inversion density n achievable employing optical pumping in an Nd: YAG crystal for a photon density p in the field of the laser light (see experiment UE4070310) also needs to take into account the population density in the ground state of the Cr: YAG crystal.
• Due to the extremely rapid increase of the photon density, both the pumping rate and the rate of spontaneous emission can be disregarded.

The threshold for the inversion density is defined as follows:

• This implies that the change in inversion density n and the photon density p over time is given by.
• In a giant pulse, the inversion density is approximately constant and remains almost equal to the initial inversion density.
• Equation (2b) can then be used to determine the photon density.
• The inversion density ni for a giant pulse is very much greater than the threshold inversion density nS.
• That means that the time it takes for the photon density to increase is much shorter than the time constant τres for resonator losses.
• Another key point in time is reached when the inversion density falls back to the threshold level. Then the photon density ceases to change as described in equation (2b), i.e. no more laser photons are generated. Equation (2a) then gives us.
• The photon density therefore falls after reaching its maximum with a time constant equal to that for the resonator losses.
• The maximum value for the photon density is given by the following.
• This means that lasers with an upper laser level that has a very short lifetime, i.e. which only have a very small excess inversion density, do not exhibit any significant increase in output power when used in pulsed mode.
• In this experiment the Cr: YAG module is added to the resonator and fine adjustment of the laser is carried out anew. The laser signal is measured using a PIN diode and traced on an oscilloscope.
• Fig. 1: Pulse over some time for an Nd: YAG laser with passive Q-switching
• OPTICS LASER PHYSICS Q-Switching for Nd: YAG Laser
• Q-Switching for Nd: YAG Laser  LASER PHYSICS OPTICS

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