Laser Info Template
Laser Info
Modulating Lasers
Whether the output from your laser is Constant Wave (CW) or Q-switched, it’s possible that you may need to control the laser’s behavior in some way. If you need to pulse or trigger the laser, or control the output power dynamically, then you require some form of modulation. Each modulation technique has its own benefits and drawbacks, so choosing the right type of modulation for your application is a critical step in designing your system.
Embedded Electronic Modulation
Many of our laboratory lasers feature electronic modulation, which is built into the driver circuit. This type of modulation is the easiest to use because it requires little additional equipment. All you need is a function generator to produce the modulation signal. The electronic modulation circuit controls the power delivered to the laser diode, so it is directly turning the laser on and off. This type of modulation can also control the output power of the laser by reducing the electrical power delivered to the laser diode. The maximum response frequency of this type of modulation is usually around 30 kHz, though this varies by model and some may be lower. The two types of electronic modulation are TTL and analog.
TTL:
Accepts a 0-5 VDC square-wave signal and can turn the laser on and off rapidly. Does not allow the user to adjust the power. The laser will pulse at full power.
Analog:
Accepts an arbitrary 0-5 VDC input signal. The laser’s output power will track the amplitude of the input signal, within the limits of the maximum response frequency.
| Advantages | Disadvantages |
– Already included with many lasers. – Requires only a simple function generator to provide the modulation signal. – Analog modulation allows for dynamic power control. – Full extinction when laser is modulated to zero. – Diode lasers produce clean, consistent pulses up to the specified maximum modulation frequency. | – Maximum modulation frequency limited to 30 kHz. – Because the power to the diode is being cycled, pulse shape may show undesirable artifacts, particularly with DPSS lasers. – Pulse shape tends to degrade at higher frequencies. – Rise time and fall time are limited by the laser diode’s properties. – Not compatible with more sensitive lasers. (Low-Noise, SLM, etc.) |
