Ultrafast lasers emit ultrashort pulses (USP) in the order of femtoseconds and picoseconds. Ultrafast lasers constitute pulsed sources with among the shortest pulsed light, and therefore, the highest peak power. Ultrafast laser applications require large peak powers, such as in nonlinear optics or material ablation. Chromacity’s ultrafast lasers are used for 2 photon microscopy, which is a nonlinear optical effect, requiring high pulse energies.
An Optical Parametric Oscillator (OPO) is a source of coherent light with a tunable frequency. An OPO consists of a nonlinear crystal placed inside a cavity which is pumped by a fixed frequency laser. Discover more about Chromacity’s picosecond OPOs which span the short to long wavelength regions.
In the OPO, the nonlinear crystals split a high-frequency beam into two low-frequency beams. One of these beams reverberates in the cavity, which amplifies the magnitude of the beam splitting effect. By tuning the parameters of the cavity, Chromacity can change the ratio of power, and therefore the frequency of the two beams. A partially reflective mirror at the end of the cavity permits partial transmission of the low energy beam, delivering a source of tunable frequency light.
Optical Parametric Oscillators can be used to generate light in frequencies that conventional lasers cannot easily access. Furthermore, most lasers have a fixed wavelength, whereas a tunable OPO can deliver light over very wide ranges, giving it far greater versatility than a laser. Applications for an OPO make use of these two features. Spectroscopy in particular uses frequencies lasers cannot produce, or across a wider range of frequencies than a laser can achieve.
In an Optical Parametric Oscillator, one of the beams reverberates in the cavity, which amplifies the conversion process and enables the delivery of higher intensity tunable light. In an Optical Parametric Amplifier (OPA) there is no reverberation. Consequently, the intensity of the tunable light delivered is much lower than an OPO.
A nonlinear crystal has a material response to applied electric fields that is nonlinearly proportionate to the applied field. This material response gives rise to unique phenomena when strong electric fields are applied, as in high-intensity ultrashort-pulses or highly focussed light. One of these phenomena is the conversion process that is important for the parametric generation of light.
The parametric generation is a process that makes use of high-intensity, coherent light to generate a range of nonlinear effects in certain optical materials. When a weak, low energy beam and a high energy pump beam interact with enough intensity within these non-linear materials, pump photons can convert to signal and idler photons (where the energy of the idler wavelength is the difference between the signal and pump energies).
Semiconductors like Gallium Phosphide have high transparency in the mid-infrared compared to traditional nonlinear crystals, making them highly suitable for generating light in the mid-infrared. An OPGaP OPO is a source of tunable light that incorporates an OPGaP (orientation patterned gallium phosphide) nonlinear crystal to generate coherent tunable light across the 4.5-12 µm region. OPGaP is a relatively new nonlinear material that has been shown to display a very non-linear coefficient when optically pumped at 1 µm.
Quantum Cascade Lasers (QCL) emit light in the mid-IR, typically between 5 – 6 µm. These semiconductor-based lasers offer a narrow bandwidth at low pulse energies. An optical parametric oscillator delivers more high average power across a broad tuning range, which is more effective for long-range stand-off detection and identifying complex chemical compounds, much further into the mid-IR, in comparison to using multiple QCLs to achieve similar results.
Fiber lasers have the benefit of being able to generate high optical gain within the active fiber. This is because the pump light can be confined within the fiber. This leads to an efficient lasing process. Short-pulse fiber laser architectures suffer from spectral broadening, where different spectral components travel at different velocities, thus causing the short pulse to broaden.
The design that Chromacity has developed makes use of a part fiber, part free space laser architecture. This allows Chromacity to benefit from creating a high average power from the active fiber section whilst being able to control the intracavity dispersion of the laser pulses in the free space section, where we can insert dispersion compensating optics.
The efficiency of our systems ensures that Chromacity can provide a compact ultrafast source that does not need to be water-cooled and has a very simple user interface. The simple cavity design also lends itself to be stable; and robust and affordable. This is in contrast to Ti:sapphire laser systems, which are complex, bulky, and expensive to operate. While ti:sapphire lasers can suit certain applications that demand tunability, they are much less appealing for fixed wavelength applications.
Light from a laser source converts into a wide spectral bandwidth where the C wavelength significantly broadens to generate a supercontinuum source. The power can be spread over many hundreds of wavelengths, however, it also means that the power in each nm of bandwidth is typically low.
Supercontinuum lasers have comparable applications to OPO’s operating in the same range because they can deliver a large range of wavelengths. By applying a bandpass filter, users can select an individual wavelength for multispecies spectroscopy, or remove the filter for illumination across the entire supercontinuum range where a white light source is desired.
A mode-locked laser is a system capable of delivering pulses of light between 10^-10 and 10^-15 seconds in length. A laser cavity of a particular length can support multiple modes, which slip in and out of phase with each other as they travel through the cavity. Where these elements constructively interfere, they form a pulse that reverberates in the laser cavity. By selectively amplifying only this pulse, users can produce high-intensity laser light with pulse lengths much shorter than traditional modulation would permit.
Active mode-locking describes the situation where an external drive is applied to the laser cavity to cause mode-locking and this can be done by modulating either the intracavity loss or the intracavity phase. In contrast, passive mode-locking involves no external modulation, but instead, the cavity contains an element whose optical loss decreases as the power incident on it increases (ie. a nonlinear loss). This self-amplitude modulation effect can be considered as being similar to an external amplitude modulation driven at exactly the cavity frequency.
A fiber coupler is a piece of optical equipment that focuses a laser beam into an optical fiber. Fiber coupling can allow researchers to deliver a laser beam to places otherwise difficult to access, through a complex laboratory set-up, industrial settings, or via a catheter into the brain or heart. Chromacity has achieved coupling efficiencies of over 90% at 4.5 W of input power, and our innovative hollow core technology allows Chromacity to deliver pulses of under 150fs with negligible spectral or temporal broadening.
A light pulse can be described as a packet of waves, bundled together in a group. The time this group takes to travel an optical path, whether it is through free space or a length of optical fiber, is known as the group delay. Dispersion is the differences in delay for the varying wavelengths present in the pulse, caused by interactions between the pulse and the optical fiber it travels. As a pulse experiences GDD, it will lengthen and acquire chirp, limiting the shortness of the pulse.
GDD compensation is how researchers compensate for the chirp that dispersive materials apply to a pulse. We apply an opposite chirp, shortening the broadened pulse. Its even possible to precompensate for dispersive optics (such as in a microscope or an optical system) further along the beam path by negatively chirping the pulse. This is achieved with the use of anomalous dispersion optics, such as curved mirrors, dispersion gratings, prisms and anomalously dispersive fiber.
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