阅读说明：本技术 利用现有飞秒激光器的用于三光子显微镜的微焦耳放大器系统 (Micro-joule amplifier system for three-photon microscope using existing femtosecond laser ) 是由 P·芬德尔 于 2019-10-04 设计创作，主要内容包括：本文公开了将广泛使用的用于2p显微镜的高重复率激光器转换成可以用于3p显微镜的光源的附加装置的想法。附加件包括这样的装置,即：该装置用以将高重复率(>50MHz)激光源(激光器或OPO)的脉冲重复率降低到小于10MHz,这允许更高的脉冲能量同时保持合理的平均功率。如果高重复源在1250nm以下操作,则附加件在放大之前将种子光移位或加宽以覆盖1.3μm至1.8μm。如果高重复率源以1.3μm或约1.3μm操作,则附加件仅需要在下调重复率之后放大脉冲。在另一实施方案中,附加件在放大之前将1.3μm光移位或加宽以覆盖外至1.8μm的光谱范围。(Disclosed herein is the idea of converting a widely used high repetition rate laser for 2p microscopy into an add-on device that can be used for the light source of 3p microscopy. The attachment piece comprises means for: the device is used to reduce the pulse repetition rate of a high repetition rate (>50MHz) laser source (laser or OPO) to less than 10MHz, which allows higher pulse energies while maintaining reasonable average power. If the high repetition source is operated below 1250nm, the appendage shifts or widens the seed light to cover 1.3 μm to 1.8 μm prior to amplification. If the high repetition rate source is operating at 1.3 μm or about 1.3 μm, the appendage only needs to amplify the pulse after the repetition rate is adjusted downward. In another embodiment, the add-on shifts or broadens the 1.3 μm light to cover the spectral range out to 1.8 μm prior to amplification.)

1. An amplifier system, comprising:

an Optical Parametric Oscillator (OPO) (110), the Optical Parametric Oscillator (OPO) (110) producing optical pulses having a first repetition rate, a tuning range between 650nm and 1400nm, and an average power >1W at a peak of the tuning range;

a pulse picking arrangement (120), the pulse picking arrangement (120) being configured to reduce the pulses from the first repetition rate to a second repetition rate;

a pulse stretching module (130), the pulse stretching module (130) configured to increase a pulse duration of pulses from the pulse picking apparatus;

an amplifier (140), the amplifier (140) configured to provide gain to longer duration pulses; and

a pulse compression module (150), the pulse compression module (150) configured to reduce a pulse duration of the amplified pulse.

2. The amplifier system of claim 1, wherein the OPO generates femtosecond pulses having a repetition rate greater than 50 MHz.

3. The amplifier system of claim 1, wherein the pulse picking arrangement is a pockels cell or an acousto-optic modulator (AOM).

4. The amplifier system according to claim 1, wherein said system generates pulse energy in the order of micro joules and is capable of amplifying several 10nm bandwidths and operating between 1250nm and 1800 nm.

5. The amplifier system of claim 1, wherein the amplifier comprises one or more amplifier stages.

6. The amplifier system of claim 1, wherein the pulse compression module is configured to compress the pulse to output a negatively chirped pulse.

7. The amplifier system of claim 1, wherein light from the OPO is spectrally broadened or frequency shifted in a highly nonlinear fiber to cover a spectral region of 1700nm to 1800 nm.

8. An amplifier system, comprising:

a femtosecond laser (210), the femtosecond laser (210) outputting optical pulses having a first repetition rate, a tuning range between 650nm to 1200nm, and an average power >1W at a peak of the tuning range;

a wavelength shifting module (220), the wavelength shifting module (220) configured to shift or broaden a wavelength of the optical pulse;

a pulse picking arrangement (120), the pulse picking arrangement (120) being configured to reduce the pulses from the first repetition rate to a second repetition rate;

a pulse stretching module (130), the pulse stretching module (130) configured to increase a pulse duration of pulses from the pulse picking apparatus;

an amplifier (140), the amplifier (140) configured to provide gain to longer duration pulses; and

a pulse compression module (150), the pulse compression module (150) configured to reduce a pulse duration of the amplified pulse.

9. The amplifier system of claim 8, wherein the wavelength-shifting module is a Photonic Crystal Fiber (PCF) configured to broaden the spectrum to cover a desired wavelength range.

10. The amplifier system of claim 8, wherein the optical module is configured to shift or widen the output of the femtosecond laser to cover a spectral range of 1250nm to 1800 nm.

11. The amplifier system of claim 8, wherein light from the femtosecond laser undergoes pre-amplification before entering a frequency shifting module.

12. The amplifier system of claim 8, wherein light from the femtosecond laser does not go to the pulse stretching module before entering the amplifier.

13. The amplifier system of claim 8, wherein the pulse picking arrangement is positioned before the wavelength shifting module.

14. The amplifier system of claim 8, wherein the pulse picking arrangement is positioned after the wavelength shifting module.

15. The amplifier system of claim 8, wherein light from the femtosecond laser is frequency shifted.

16. The amplifier system of claim 15, wherein the frequency shifted light goes to the pulse stretching module before entering the amplifier.

17. The amplifier system of claim 15, wherein the frequency shifted light does not go to the pulse stretching module before entering the amplifier.

Technical Field

The present invention relates generally to amplifier systems for multiphoton microscopes, and more particularly to micro-joule amplifier systems for three-photon microscopes that utilize an existing femtosecond laser for two-photon microscopes as a seed source.

Background

In life sciences, fluorescence microscopy is used to study biological samples such as single cells or to study complex structures (e.g., the brain). The scattering in these samples limits the imaging depth. It is often the case that light having longer wavelengths is scattered less in tissue, thus allowing it to penetrate deeper into, for example, the brain. Two-photon (2p) microscopes take advantage of this and allow imaging to a depth of about 1mm, for example, in the brain. In two-photon microscopy, the wavelength required to excite a fluorophore or fluorescent protein is doubled compared to single-photon excitation, as used, for example, in confocal microscopy. Three photon (3p) microscopes further take one step of the method by using even longer wavelengths of light. A disadvantage from single-photon to two-photon to three-photon excitation is that the probability of such an event becoming smaller and smaller, and therefore a greater laser intensity is required. For a 3p microscope, a μ J laser pulse generating megawatts of peak power is required. Systems capable of generating these peak power levels are expensive and operate at low repetition rates.

However, in addition to 3p imaging capability, most scientists also require the ability to perform 2-photon imaging in order to acquire images at high frame rates to capture dynamic processes. 3p are only needed when they need to be deep into the sample. 2p lasers are the working mainstay in most neuroscience laboratories. The inventive concept behind this disclosure is to produce a device that can be used in conjunction with a ubiquitous 2p light source to produce pulses of light in the muj state.

Disclosure of Invention

Disclosed herein is an idea to produce an add-on device that converts a widely used high repetition rate laser for 2p microscopy into a light source that can be used for 3p microscopy. The attachment piece comprises means for: the device is used to reduce the pulse repetition rate of a high repetition rate (>50MHz) laser source (laser or OPO) to less than 10MHz, which allows higher pulse energies while maintaining reasonable average power. If the high repetition source is operated below 1250nm, the appendage shifts or widens the seed light to cover 1.3 μm to 1.8 μm prior to amplification. If the high repetition rate source is operating at 1.3 μm or about 1.3 μm, the appendage may only need to amplify the pulse after the repetition rate is adjusted downward. In another embodiment, the add-on shifts or broadens the 1.3 μm light to cover the spectral range out to 1.8 μm prior to amplification.

The novelty here is that the add-on system converts a common 2p laser system to a 3p laser system, providing the customer with unique value, since the customer can enjoy the benefits of both technologies.

In one embodiment, the present invention provides an amplifier system comprising: an Optical Parametric Oscillator (OPO) that generates optical pulses having a first repetition rate; a pulse picking arrangement configured to reduce pulses from a first repetition rate to a second repetition rate; a pulse stretching module configured to increase a pulse duration of pulses from the pulse picking means; an amplifier configured to provide gain to the longer duration pulses; and a pulse compression module configured to reduce a pulse duration of the amplified pulse.

In one embodiment, the present invention provides an amplifier system comprising: a femtosecond laser that outputs optical pulses having a first repetition rate; a wavelength shifting module configured to shift or widen a wavelength of the optical pulse; a pulse picking arrangement configured to reduce pulses from a first repetition rate to a second repetition rate; a pulse stretching module configured to increase a pulse duration of pulses from the pulse picking means; an amplifier configured to provide gain to the longer duration pulses; and a pulse compression module configured to reduce a pulse duration of the amplified pulse.

Drawings

Fig. 1 is a block diagram of an amplifier system according to an embodiment of the invention.

Fig. 2 is a block diagram of an amplifier system according to another embodiment of the invention.

Detailed Description

The description of illustrative embodiments in accordance with the principles of the invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In describing the various embodiments of the invention disclosed herein, any reference to direction or orientation is made for convenience of description only and does not limit the scope of the invention in any way. Relative terms such as "lower," "upper," "horizontal," "vertical," "above," "below," "upward," "downward," "top" and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as "attached," "connected," "coupled," "interconnected," and the like refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Furthermore, the features and benefits of the present invention are described with reference to exemplary embodiments. Therefore, the invention expressly should not be limited to such exemplary embodiments: it shows some possible non-limiting combinations of features that may be present alone or in other combinations of features; the scope of the invention is defined by the appended claims.

The instant disclosure describes the best mode or modes presently contemplated for carrying out the invention. This description is not intended to be construed in a limiting sense, but rather provides examples of the invention presented for illustrative purposes only by reference to the figures, so as to suggest themselves to those skilled in the art of the advantages and construction of the invention. The same reference numbers will be used throughout the drawings to refer to the same or like parts.

The first idea proposed here is to use the existing high repetition rate (>50MHz) femtosecond source based on optical parametric oscillators as a seed source for lower repetition rate amplifiers generating pulse energies in the order of micro joules, which can amplify a few 10nm bandwidth and operate between 1250nm and 1800 nm. As shown in fig. 1, the means 120 for reducing the pulse repetition rate is disposed between the OPO 110 and the amplifier 140. The device may be a pockels cell or an acousto-optic modulator (AOM). Pulse picking apparatus 120 is followed by a pulse stretching module 130, which pulse stretching module 130 reversibly increases the pulse duration from a femtosecond state to a picosecond (1ps to 1000ps) time scale in order to reduce the peak power of the laser pulses. The module 130 is followed by one or more amplifier stages 140. The amplifier stage may be based on optical fibers, optical fiber rods, bulk glass or crystals. The gain process may be parametric or nonparametric. Amplifier stage 140 is followed by a pulse compression module 150, which pulse compression module 150 reduces the pulse duration to the femtosecond order again. An optional wavelength shifting module 160 may be disposed between the OPO 110 and the pulse picking module 120.

In another embodiment, compression may have the ability to overcompensate so that the output pulse is negatively chirped, i.e., the higher frequency is at the leading edge of the pulse. The aim is to pre-compensate the dispersion in a 3p microscope.

In another embodiment, the original seed light from the OPO is either spectrally broadened in a highly nonlinear fiber or shifted to cover the 1700nm to 1800nm spectral region before amplification. The widening may occur after or before changing the repetition rate.

As shown in fig. 2, the second idea proposed is to use a femtosecond laser 210 operating below 1.2 μm as a seed source for the μ J amplifier system. Thus, the wavelength of the high repetition rate source needs to be shifted or broadened by the wavelength shifting module 220 to cover the spectral range of 1250nm to 1800 nm. An optional preamplifier module 230 may be positioned between the femtosecond laser 210 and the wavelength-shifting module 220. The widening may or may not require additional pre-amplification. In one embodiment, a Photonic Crystal Fiber (PCF) may be used to broaden the spectrum to cover the desired range. The pulse picking means may be arranged before or after the widening stage. The output of the PCF may benefit from spectral filtering to optimize overlap with the gain spectrum. The seed light may or may not go to the pulse stretching module before entering the amplification stage.

In another embodiment, the light of the high repetition rate source is frequency shifted by a non-linear process such as Raman frequency shifting before being used as a seed pulse. After the frequency shift, the light may or may not go to the pulse stretching module before entering the amplification stage.

While the present invention has been described with a certain length and a certain particularity with respect to the several described embodiments, it is not intended to limit the invention to any such detail or embodiment or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in light of the prior art and, therefore, to effectively encompass the intended scope of the invention. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.