Frequency Doubling: Typical Conversion, Input Power & CW Laser?

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In summary, frequency doubling methods have varying efficiencies, with some methods achieving up to 50% efficiency. The conversion from 1064nm to 532nm is typically second order and dependent on the input power and the type of nonlinear crystal used. Efficiency increases quadratically with input power and there are specific crystals cut for certain wavelengths. While second harmonic generation can work for continuous wave lasers, it is most effective for short pulses and not as effective for low input powers. The availability of diode lasers with narrow linewidths in the red suggests that there may be a need for more efficient doubling methods to expand the range of wavelengths used in experiments.
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Thermodave
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I'm trying to get an idea of how efficient frequency doubling methods are. I quick google search gives back everything from .01% to above 50%. What is the typical conversion from 1064 to 532? Is this common for other wavelengths/crystals? More importantly, why does it sound like the efficiency is related to input power? Can low power cw laser be doubled? Thanks for any info.
 
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In nonlinear optics you develop the response P to a light field of amplitude E in a power series of the field amplitude:
[tex]P(t)=\chi^{(1)} E(t) +\chi^{(2)}E^2 (t) +\chi^{(3)}E^3 (t)+...[/tex]

Second harmonic generation/frequency doubling is a second order process and therefore proportional to the square of the amplitude of the incoming field. Therefore its efficiency increases also quadratically with the amplitude.

The efficiency also depends strongly on what nonlinear crystal you use and which wavelength you are aiming at. There are good crystals cut for 800nm->400nm achieving up to 20% efficiency. I am sure the record values are way higher, but not representative.

As a consequence SHG works best for short pulses. SHG for cw is of course also possible but not very effective, even worse for low input powers. What input power and wavelength are you considering exactly?
 
  • #3
Higher peak powers generally allow higher efficiencies. But they can also give rise to other issues.
 
  • #4
Cthugha said:
In nonlinear optics you develop the response P to a light field of amplitude E in a power series of the field amplitude:
[tex]P(t)=\chi^{(1)} E(t) +\chi^{(2)}E^2 (t) +\chi^{(3)}E^3 (t)+...[/tex]

Second harmonic generation/frequency doubling is a second order process and therefore proportional to the square of the amplitude of the incoming field. Therefore its efficiency increases also quadratically with the amplitude.

The efficiency also depends strongly on what nonlinear crystal you use and which wavelength you are aiming at. There are good crystals cut for 800nm->400nm achieving up to 20% efficiency. I am sure the record values are way higher, but not representative.

As a consequence SHG works best for short pulses. SHG for cw is of course also possible but not very effective, even worse for low input powers. What input power and wavelength are you considering exactly?


Thank you for the explanation. I wasn't thinking a specific experiment though. I've just noticed that there are a lot of diode lasers (e.g. New Focus 25mW cw) models on the market now with narrow linewidths that can be used for absorption experiments but that they are all in the red. If there was an efficient doubling approach than I'm sure we'd be seeing a broader range of wavelengths. Doing absorption spec in the 300s would be convenient, if it was tunable of course.
 

1. What is frequency doubling and how does it work?

Frequency doubling is a process in which the frequency of a laser beam is doubled by passing it through a nonlinear optical crystal. This crystal has the property of generating new frequencies when exposed to intense laser light, resulting in a beam with twice the original frequency.

2. What is the typical conversion efficiency of frequency doubling?

The typical conversion efficiency of frequency doubling varies depending on the type of crystal used and the input power of the laser. It can range from a few percent to over 50%, with higher efficiencies achieved with higher input powers and specific crystal orientations.

3. What is the minimum input power required for frequency doubling?

The minimum input power required for frequency doubling depends on the type of crystal and the desired output power. In general, a minimum input power of a few watts is needed for efficient frequency doubling, but this can vary significantly depending on the specific application and crystal properties.

4. Can frequency doubling be achieved with continuous wave (CW) lasers?

Yes, frequency doubling can be achieved with CW lasers. However, the input power of the laser must be carefully controlled to prevent thermal damage to the crystal and ensure efficient frequency conversion.

5. What factors can affect the performance of frequency doubling?

The performance of frequency doubling can be affected by several factors, including the type and quality of the nonlinear crystal, the input power and stability of the laser, and the alignment and temperature of the crystal. Other external factors such as air turbulence and vibrations can also impact the performance of frequency doubling.

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