10 Questions You Should to Know about acousto-optic q-switch driver

Acousto-optic Q Switches

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Acousto-optic modulators (AOMs) are specialized for Q switching lasers by being placed inside the laser resonator. Powered by an RF input, these AOMs increase the diffraction losses of light circulating in the resonator, thus suppressing lasing. When the RF input is abruptly turned off, an intense laser pulse is released.

Most Q-switched solid-state lasers use an acousto-optic Q switch. Only a few utilize electro-optic Q switches for the highest switching speeds or very high loss modulations.

Figure 1: A compact acousto-optic Q-switch. Source: Gooch & Housego.

Requirements on Acousto-optic Q switches

General requirements for AOMs include low insertion loss for the zero-order beam, high surface quality of the acousto-optic medium (like fused silica), and the use of anti-reflection coatings.

• Insertion loss should be minimal to prevent power losses and thermal effects. This requires a loss-absorption acousto-optic medium.
• The device should maintain identical input and output polarization, even when dealing with isotropic or non-isotropic acousto-optic media.
• The modulator must have a high damage threshold to withstand intense laser pulses.
• It should ensure high diffraction losses in the 'on' state to suppress lasing effectively.
• The switching speed must be fast enough for clean pulse build-up.
• The device should be capable of operating under a high duty cycle typical for laser applications.

There are trade-offs involved in the performance of AOMs. For instance, tellurium dioxide (TeO2) offers high elasto-optic coefficients but a moderate damage threshold, while crystalline quartz can withstand higher intensities but at the expense of higher acoustic power.

In high-gain lasers like fiber lasers, the first-order diffracted beam can be used under lasing conditions to create very high resonator losses when the AOM is off.

RF Drivers for Acousto-optic Q switches

The electronic driver usually operates with a fixed modulation frequency and a digital input for rapid RF output switching.

The required RF drive power is significant, often exceeding 10 W, due to factors like substantial loss modulation, low acousto-optic figure of merit, and large acoustic beam diameter.

As RF power converts to heat, water cooling of AOMs is often necessary.

Frequently Asked Questions

1. Which parameters do I need to specify if I want to order a Q-Switch?

You need to specify the frequency, aperture, acoustic mode, and type of water connector.

2. Which frequency should I use?

The frequency depends on your region's regulatory guidelines. Historically, 24.0 MHz has been used in the USA and Japan, and 27.12 MHz is common in Europe. However, 27.12 MHz is now also used widely in the USA.

3. What is the difference between clear aperture and active aperture?

The clear aperture relates to the size of the silica block, while the active aperture refers to the height of the acoustic beam inside the block.

4. How do I select the appropriate aperture for my application?

Generally, the active aperture should match the laser's beam diameter. Using a smaller aperture Q-Switch can reduce RF power needs, improve efficiency, and may even allow for a lower cost driver.

5. Which acoustic mode would suit me best?

Choose shear mode for unpolarised lasers and compressional mode for polarised systems for better efficiency and beam quality.

6. Which water connector should I choose?

Screw-on connectors are traditionally used, but push-on fittings are often preferred for better flow and ease of use.

7. How do I know that the Q-Switch is not over-heating?

Q-Switches are equipped with a thermal interlock. If the temperature exceeds 50 degrees C, the driver shuts down to prevent damage.

8. What is the optimum operating temperature of the Q-Switch?

The temperature should be set slightly above ambient, around 32 degrees C, to prevent condensation and maintain performance.

9. How do I know that the QS24/27 Series Q-Switch is the best choice for my application?

Consult with our engineers. The QS24/27 Series Q-Switches are reliable and optimized for Nd:YAG and high-power industrial diode-pumped lasers.

10. I'm designing a compact laser and the QS24/27 Series Q-Switch is too large. What should I do?

Consider our range of standard compact Q-Switches or contact us for a custom-designed solution.

For more details, kindly visit introduction to radiation detectors.

For more information on acousto-optic Q-switches, please visit acousto-optic q-switch driver.