Laser with optical fiber frequency doubling pumping source

Abstract

The invention relates to a laser. An exemplary laser includes a pump source to generate pump laser light; the oscillator is used for outputting femtosecond laser under the excitation of the pumping laser; and the carrier envelope phase deviation frequency measuring device is used for measuring the carrier envelope phase deviation frequency of the femtosecond laser, and the pumping source is an optical fiber frequency doubling pumping source.

Description

Technical Field

[0001] The present disclosure generally relates to the field of ultrafast laser technology, and more specifically, to a laser with a fiber frequency doubling pump source. Background Art

[0002] Femtosecond (fs) lasers have practical value in many fields such as laser micromachining, two-photon imaging in biomedicine, surgical operations, precision detection, and femtochemistry. Since the 1990s, titanium-doped sapphire (Ti:Sapphire) pump sources have been the main light sources for ultrafast phenomenon research because of their wide gain bandwidth and the ability to achieve laser output with a pulse width less than 10 fs. The main absorption peak of the absorption spectrum of the titanium sapphire crystal is near 488 nm, and the emission peak of the emission spectrum is near 780 nm.

[0003] Lasers can use argon ion pump sources. Argon ion pump sources are an inert gas pump source that emits wavelengths of 488 nm or 514.5 nm. They are currently the pump sources with the highest continuous output power in the visible light region, with a maximum output power of over one hundred watts. Their disadvantages are that the degree of ionization during gas discharge is not high, and the quantum efficiency is relatively low, so the energy conversion efficiency is low, generally between 0.001% - 0.01%, and they have defects such as large size, complex structure, and difficult maintenance.

[0004] Semiconductor pump sources with emission wavelengths in the blue-green light band can also be used as pump sources for titanium sapphire lasers. Semiconductor pump sources have advantages such as low price, small size, high efficiency, and long lifespan. Generally, they have two types: edge-emitting and surface-emitting, but their output light spots are very poor, the light beam has fast and slow axes, and beam shaping is required during use.

[0005] Currently, frequency-doubled all-solid-state pump sources are the most widely used pump sources for titanium sapphire lasers. This type of pump source outputs fundamental frequency pump laser with a wavelength of 1064 nm from an Nd:YVO4 pump source, and obtains continuous light with a wavelength of 532 nm through frequency doubling by a nonlinear crystal. Currently, a maximum green light output of 20 W has been achieved. The disadvantages are that such pump sources are relatively expensive, and the output wavelength deviates far from the main absorption peak of titanium sapphire, and the efficiency is average.

[0006] Therefore, in the prior art, the wavelength of the commonly used pump light is far from the peak value of 488 nm of the absorption peak of titanium sapphire, and its absorption efficiency is not high. In addition, to obtain a laser pulse output with a sub-10 femtosecond, fine dispersion compensation is also required. Summary of the Invention

[0007] The present disclosure provides a laser, which may include: a pump source for generating pump laser; an oscillator for outputting femtosecond laser under the excitation of the pump laser; and a carrier-envelope phase offset frequency measurement device for measuring the carrier-envelope phase offset frequency of the femtosecond laser, wherein the pump source may be a fiber frequency-doubling pump source.

[0008] In some embodiments, the laser may further include a carrier-envelope phase offset frequency locking device for locking the carrier-envelope phase offset frequency. The carrier-envelope phase offset frequency locking device may include: a phase-locked loop circuit for calculating a frequency error signal of the carrier-envelope phase offset frequency of the femtosecond laser measured by the carrier-envelope phase offset frequency measurement device relative to a reference frequency; and an acousto-optic modulator located in the optical path between the pump source and the oscillator, receiving the frequency error signal output by the phase-locked loop circuit, and adjusting the carrier-envelope phase offset frequency by modulating the power of the pump laser.

[0009] In some embodiments, the carrier-envelope phase offset frequency measurement device is a self-heterodyne 0-f module. The pulse width of the femtosecond laser input from the oscillator is less than 10 femtoseconds. The femtosecond laser with a pulse width less than 10 femtoseconds is subjected to self-phase modulation, difference frequency, and spectral broadening, and the broadened spectrum is subjected to beat frequency to generate a beat frequency signal. The carrier-envelope phase offset frequency is the frequency of the beat frequency signal.

[0010] In some embodiments, the pump source may be a sub-10-femtosecond titanium sapphire pump source, the wavelength of the generated pump laser is 515 nanometers, and the pump laser is single-mode output.

[0011] The above and other features and advantages of the present disclosure will become apparent from the following description of specific embodiments in conjunction with the accompanying drawings. Description of the Drawings

[0012] Figure 1 A structural diagram of a pump source and an oscillator of a laser according to an exemplary embodiment of the present disclosure is shown.

[0013] Figure 2 A schematic diagram of a mode-locked spectrum realized by a pump source and an oscillator of an exemplary embodiment is shown.

[0014] Figure 3 A structural diagram of a laser according to an exemplary embodiment of the present disclosure is shown.

[0015] Figure 4 An accurately dispersion-compensated laser spectrum obtained by a laser of an exemplary embodiment is shown.

[0016] Figure 5Shows the beat frequency signal obtained by the laser of the exemplary embodiment.

[0017] Figure 6 Shows the measurement results of the locking accuracy of the carrier-envelope phase locked by the laser of the exemplary embodiment. Detailed implementation manners

[0018] Hereinafter, example embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Note that the drawings may not be drawn to scale. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure, and the present disclosure is not limited by the example embodiments described herein.

[0019] An example embodiment of the present disclosure provides a laser with a fiber frequency-doubled pump source, which can achieve the locking of the frequency of a low-noise carrier-envelope phase offset (CEO). For the same titanium sapphire crystal, the closer the pump wavelength is to the main absorption peak, the higher its absorption efficiency. The laser according to the exemplary embodiment adopts a fiber frequency-doubled pump source, so that the pump wavelength is close to the main absorption peak, thereby enabling the crystal to fully absorb the pump energy, improving the optical-optical conversion efficiency, reducing noise, and achieving the locking of the CEO frequency.

[0020] Figure 1 Shows the structural diagram of the pump source and the oscillator of the laser according to the exemplary embodiment of the present disclosure. As Figure 1 shown, the laser according to the exemplary embodiment of the present disclosure has a pump source 101 and an oscillator 130. The exemplary pump source 101 may be a fiber frequency-doubled pump source for generating pump laser. In some embodiments, the pump source 101 may be a sub-10 femtosecond titanium sapphire pump source for pumping the titanium sapphire crystal to achieve population inversion and Kerr lens self-mode locking operation. The wavelength of the generated pump laser is, for example, 515 nm, which is closer to the absorption peak (488 nm) of the titanium sapphire crystal compared with the commonly used 532 nm wavelength laser, and the pump laser is single-mode output.

[0021] In some embodiments, the pump source 101 may be, for example, a low-noise pump source with stable power, and its root mean square (RMS) is, for example, less than 1%.

[0022] In some embodiments, the maximum output power of the pump source 101 may be, for example, 5.5 W, the power stability is less than 0.5%, and the beam quality is approximately equal to 1.

[0023] The oscillator 130 can be used to output femtosecond-level laser under the excitation of the pump laser. As Figure 1As shown, the exemplary oscillator 130 may include: a first mirror 102, a second mirror 103, a convex lens 104, a first concave mirror 105, a crystal 106, a second concave mirror 107, a third mirror 108, a fourth mirror 109, a fifth mirror 110, a sixth mirror 111, a first wedge 112, a second wedge 113, an output coupling mirror 114, a seventh mirror 115, an eighth mirror 116, a third wedge 117, and a fourth wedge 118.

[0024] The first mirror 102 may be, for example, a high-reflection mirror, which can reflect the pump laser generated by the pump source 101 to the second mirror 103. The second mirror 103 may be, for example, a high-reflection mirror, which can reflect the pump laser to the convex lens 104. The convex lens 104 may be, for example, a plano-convex thin lens, which can be used to focus and couple the pump laser.

[0025] The pump laser focused by the convex lens 104 can pass through the first concave mirror 105. In Figure 1 it, the optical path of the pump laser generated by the pump source 101 that can pass through the first concave mirror 105 is represented by a dotted line. The radius of curvature R of the first concave mirror 105 may be, for example, 100 mm, and it can basically transmit the pump laser generated by the pump source 101. For example, the wavelength of the pump laser generated by the pump source 101 is 515 nm, and the anti-reflection rate of the first concave mirror 105 for the 515 nm band can be less than 0.25%, so that the pump laser generated by the pump source 101 can basically transmit through the first concave mirror 105. In this way, when the focal length F of the convex lens 104 is 100 mm, the pump laser focused by the convex lens 104 can reach the crystal 106 after transmitting 105 mm in the air. That is, the convex lens 104 focuses the pump laser onto the crystal 106.

[0026] On the other hand, the first concave mirror 105 may have a high reflectivity for beams in the 640 - 1000 nm band, for example, greater than 99.8%, and can provide -70 fs 2 ±30 fs 2 of group delay dispersion in the 720 - 1000 nm band. Thus, the beam that returns to the first concave mirror 105 after passing through the crystal 106 can be basically reflected to the sixth mirror 111. In Figure 1 it, the optical path of the beam that can be reflected by the first concave mirror 105 is represented by a dashed line.

[0027] The crystal 106 can be, for example, a titanium sapphire crystal. The optical path length can be, for example, 2 mm, the doping concentration can be, for example, 0.25 wt%, and it is cut at the Brewster's angle for absorbing the pump laser energy and providing gain for the stimulated emission in the laser resonator. The crystal 106 can be, for example, wrapped with indium foil and fixed on a heat sink made of copper with a gold-plated surface. The heat sink is cooled by circulating water, and the temperature is maintained at, for example, 16 °C or 17 °C. The front end of the crystal 106 can be, for example, 50 mm away from the first concave mirror 105, and the end of the crystal 106 can be, for example, 52 mm away from the second concave mirror 107.

[0028] The radius of curvature R of the second concave mirror 107 can be, for example, 100 mm. The antireflectivity for the 515 nm band can be, for example, less than 0.25%, while it can have a high reflectivity for the 640 - 1000 nm band, for example, greater than 99.8%, and can provide, for example, -70 fs 2 ±30 fs 2 of group delay dispersion in the 720 - 1000 nm band. The distance between the first concave mirror 105 and the second concave mirror 107 can be, for example, 104 mm, and the folding angle between them can be, for example, 10°. In some embodiments, the group delay dispersion is second-order dispersion.

[0029] The first concave mirror 105 and the second concave mirror 107 can be used to ensure the mode matching between the laser beam waist on the crystal 106 and the pump laser with a wavelength of, for example, 515 nm, and provide, for example, -70 fs 2 or -40 fs 2 of group delay dispersion in the 720 - 1000 nm band. In some embodiments, the first concave mirror 105 and the second concave mirror 107 can be coated with an antireflection film for the 515 nm wavelength on the side facing outside the cavity, and a high-reflection film for the 650 - 1100 nm band on the side facing inside the cavity. The sizes of the antireflection film and the high-reflection film can be, for example, both half an inch.

[0030] The boundary of the resonator (not shown) of the oscillator 130 can be, for example, between the output coupling mirror 114 and the seventh mirror 115. For example, the first mirror 102 to the output coupling mirror 114 are inside the cavity, while the seventh mirror 115, the eighth mirror 116, the third wedge 117, and the fourth wedge 118 are outside the cavity. For the first concave mirror 105, Figure 1 the left side is the direction inside the cavity, and the right side is the direction outside the cavity; for the second concave mirror 107, Figure 1 the left side is the direction outside the cavity, and the right side is the direction inside the cavity.

[0031] After the pump laser passing through the first concave mirror 105 passes through the crystal 106, the laser beam is reflected by the second concave mirror 107 to the third reflector 108. The third reflector 108 can be, for example, a high laser reflector, which can reflect the laser beam to the fourth reflector 109. The fourth reflector 109 can be, for example, a high laser reflector, which can reflect the beam to the fifth reflector 110.

[0032] In some embodiments, the third reflector 108 and the fourth reflector 109 can have a high reflectivity of R>99.7% for lasers in the wavelength band of, for example, 510 - 920 nm, and can provide, for example, -70 fs 2 of group delay dispersion in the wavelength band of, for example, 520 - 900 nm. In some embodiments, the third reflector 108 and the fourth reflector 109 can provide -40 fs 2 of group delay dispersion in the wavelength band range of 520 - 900 nm.

[0033] In some embodiments, the fifth reflector 110 can have a high reflectivity of R>99.9% for lasers in the wavelength band of, for example, 710 - 890 nm, and provide 0 fs 2 of group delay dispersion in the wavelength band range of 720 - 880 nm or in the wavelength band range of 735 - 910 nm.

[0034] The fifth reflector 110 reflects the laser back to the fourth reflector 109, which reflects it back to the third reflector 108, which reflects it back to the second concave mirror 107, which reflects it back to the first concave mirror 105 through the crystal 106. The laser reflected back to the first concave mirror 105 will be reflected to the sixth reflector 111.

[0035] In some embodiments, the sixth reflector 111 can be, for example, a high laser reflector, which has a high reflectivity of, for example, R>99.9% for lasers in the wavelength band of 700 - 900 nm, and can provide 120 fs 2 ±70 fs 2 of group delay dispersion in the wavelength band range of, for example, 700 - 900 nm.

[0036] The distance between the third reflector 108 and the second concave mirror 107 can be, for example, 275 mm, the distance between the third reflector 108 and the fourth reflector 109 can be, for example, 380 mm, the distance between the fourth reflector 109 and the fifth reflector 110 can be, for example, 445 mm, and the distance between the sixth reflector 111 and the first concave mirror 105 can be, for example, 240 mm.

[0037] In some embodiments, the third mirror 108, the fourth mirror 109, the fifth mirror 110, and the sixth mirror 111 can all be half-inch plane mirrors, with a reflection bandwidth of, for example, 650 - 1100 nm, and a reflectivity of, for example, greater than 99.8%.

[0038] The laser reflected by the sixth mirror 111 passes through the first wedge 112 and the second wedge 113 and reaches the output coupler 114. In some embodiments, the tilt angles of the first wedge 112 and the second wedge 113 can be, for example, 2°48′, and the thickness can be, for example, 2 mm at the thickest point and 150 μm at the thinnest point, providing an adjustable group delay dispersion of, for example, +20 fs 2 to +100 fs 2 to achieve fine adjustment of the net dispersion in the laser cavity. The first wedge 112 and the second wedge 113 are placed at the Brewster angle in the cavity, with a spacing of, for example, 1.5 mm between them, for fine adjustment of the intracavity dispersion. The first wedge 112 can be, for example, 360 mm away from the sixth mirror 111.

[0039] The output coupler 114 can be, for example, a 1-mm-thick, half-inch-sized plane mirror for laser output. In some embodiments, the output coupler 114 has an output rate of 3% in the 750 - 850 nm band. For example, the output coupler 114 can be coated with a dielectric film on the side facing the cavity with a transmittance of 3% for 750 - 850 nm laser, and an antireflection dielectric film on the other side. The distance between the output coupler 114 and the second wedge 113 can be, for example, 105 mm. For the output coupler 114, Figure 1 the left side is the intracavity direction and the right side is the extracavity direction.

[0040] The laser passing through the output coupler 114 is repeatedly reflected by the seventh mirror 115 and the eighth mirror 116, and then passes through the third wedge 117 and the fourth wedge 118 and exits the oscillator 130.

[0041] The seventh mirror 115 and the eighth mirror 116 can both be chirped mirrors, for example. In some embodiments, the seventh mirror 115 and the eighth mirror 116 can provide a high reflectivity of, for example, R > 99.8% in the 650 - 1100 nm band, and the group delay dispersion in the 750 - 1000 nm band can be, for example, -70 fs 2 for extracavity compression of the pulse. In some embodiments, both the seventh mirror 115 and the eighth mirror 116 have a high reflectivity of R > 99.8% for the laser in the 640 - 1100 nm band, and the group delay dispersion provided in the 640 - 1000 nm band range can be, for example, -70 fs 2 ±20 fs 2。The laser beam can be incident on the surface of the seventh mirror 115 at an incident angle of, for example, 12°. The seventh mirror 115 and the eighth mirror 116 can be placed in parallel, and the distance between them can be, for example, 45 mm.

[0042] The inclination angles of the third wedge 117 and the fourth wedge 118 can be, for example, 2°48′, and the thickness can be, for example, 2 mm at the thickest part and 150 μm at the thinnest part. The third wedge 117 and the fourth wedge 118 can be placed at the Brewster angle on the external laser path to achieve fine adjustment for compensating the external dispersion of the compressed laser cavity. The interval between the third wedge 117 and the fourth wedge 118 can be, for example, 2 mm.

[0043] The pump source 101 of the laser according to the exemplary embodiment of the present disclosure can be, for example, a fiber frequency-doubled pump source, so as to be able to generate pump laser in the 515 nm band; in addition, in the oscillator 130, chirped mirrors can be used to compensate for the intracavity dispersion, and by setting a pair of wedges, fine adjustment of the net intracavity dispersion can be achieved, so as to be able to achieve laser pulse output with a width less than 10 femtoseconds.

[0044] The pump source 101 and the oscillator 130 of the laser according to the exemplary embodiment of the present disclosure can form a sub-10 femtosecond titanium sapphire laser oscillator pumped by 515 nm, and obtain ultrashort laser pulse output with a pulse width less than 10 fs and an average power greater than 300 mW. Pumping with a 515 nm wavelength closer to the absorption peak of the titanium sapphire crystal improves the output power. Moreover, using a dispersion compensation scheme combining chirped mirrors and wedges, the chirped mirrors provide negative group delay dispersion to compensate for the positive group delay dispersion introduced by the laser crystal and air, and the pair of wedges can adjust the fine adjustment of the net group delay dispersion in the cavity, so as to be able to obtain ultrashort laser pulse output with a pulse width less than 10 femtoseconds.

[0045] Figure 2 Show a mode-locked spectrum diagram realized by the pump source 101 and the oscillator 130 of the exemplary embodiment. Figure 2 The shown mode-locked spectrum is the mode-locked spectrum measured by a spectrometer and output from the output coupler 114, that is, output by the oscillator 130. As Figure 2 shown, the horizontal axis is the wavelength, with the unit of nanometer; the left vertical axis is the intensity shown by the dotted line in the figure, and a.u. represents non-dimensional normalized intensity; the right vertical axis is the absolute intensity obtained by taking the logarithm of the dotted line shown by the solid line in the figure, with the unit of decibel. As Figure 2 shown, a low-noise pump source 101 is used to generate pump laser, and after precise dispersion compensation in the oscillator 130, a laser spectrum of 620 - 1000 nm is obtained. As Figure 2 shown, the spectrum has higher intensities at 700 nm and 900 nm, which is beneficial to the generation of subsequent CEO signals.

[0046] Figure 3 A structural diagram of a laser according to an exemplary embodiment of the present disclosure is shown. As Figure 3 shown, the laser according to the exemplary embodiment of the present disclosure includes a pump source 301, an oscillator 303, and a CEO frequency measurement device 350. The pump source 301 may be Figure 1 the pump source 101 shown, that is, it may be a fiber frequency-doubled pump source for generating pump laser. The oscillator 303 may be Figure 1 the pump source 130 shown, for outputting femtosecond-level laser under the excitation of the pump laser. The oscillator 303 may be, for example, a titanium sapphire femtosecond oscillator. The CEO frequency measurement device 350 is used to measure the CEO frequency of the femtosecond-level laser output by the oscillator 303. In some embodiments, the CEO frequency measurement device 350 may be a self-heterodyne 0-f module.

[0047] The CEO frequency measurement device 350 may include: a first mirror 304, a second mirror 305, a third mirror 306, a fourth mirror 307, a fifth mirror 308, a pair of wedges 309, a first concave mirror 310, a frequency-doubling crystal 311, a second concave mirror 312, a filter 313, a sixth mirror 314, a plano-convex lens 315, and an avalanche photodiode (APD) 316.

[0048] In Figure 3 , the laser optical path that outputs from the oscillator 303, enters the CEO frequency measurement device 350, and outputs from the CEO frequency measurement device 350 to the outside of the laser is indicated by a dotted line. The femtosecond-level laser output by the oscillator 303 enters the CEO frequency measurement device 350, is reflected by the first mirror 304 to the second mirror 305, is reflected by the second mirror 305 to the third mirror 306, and is reflected by the third mirror 306 to the fourth mirror 307. The first mirror 304, the second mirror 305, and the third mirror 306 may be, for example, silver mirrors.

[0049] After the laser is reflected multiple times between the fourth mirror 307 and the fifth mirror 308, it is reflected by the fifth mirror 308 to a pair of wedges 309. The fourth mirror 307 and the fifth mirror 308 may be, for example, chirped mirrors. After passing through the pair of wedges 309, the laser is reflected by the first concave mirror 310 into the frequency-doubling crystal 311. The first concave mirror 310 may be, for example, a silver mirror, and the frequency-doubling crystal 311 may be, for example, a periodically poled lithium niobate crystal (PPLN). The laser frequency-doubled by the frequency-doubling crystal 311 is reflected by the second concave mirror 312 to the filter 313. The second concave mirror 312 may be, for example, a silver mirror.

[0050] The filter 313 can be, for example, a high-pass filter. Most of the laser light reflected by the second concave mirror 312 onto the filter 313 is reflected by the filter 313 out of the laser as the laser light 340 output by the laser; another part passes through the filter 313 as the laser light 330 to be measured by the CEO frequency measurement device 350. In Figure 3 , the optical path of the laser light 330 for measurement by the CEO frequency measurement device 350 is represented by a dotted line.

[0051] The laser light 330 passing through the filter 313 for measuring the CEO frequency is reflected by the sixth mirror 314 and enters the plano-convex lens 315, and is converged by the plano-convex lens 315 to the APD 316. The sixth mirror 314 can be, for example, a silver mirror. The APD 316 can measure the CEO frequency of the laser light 330.

[0052] In some embodiments, the pulse width of the femtosecond laser input from the oscillator 303 is less than 10 femtoseconds. The CEO frequency measurement device 350 performs self-phase modulation, difference frequency, and spectral broadening on the femtosecond laser with a pulse width less than 10 femtoseconds, and performs beat frequency on the broadened spectrum to generate a beat frequency signal. The CEO frequency measured by the APD 316 is the frequency of the beat frequency signal.

[0053] In some embodiments, the laser according to the exemplary embodiments of the present disclosure may further include a CEO frequency locking device 320 for locking the CEO frequency. Locking the CEO frequency is not an essential function of the laser. In other words, if the laser does not need to lock the CEO frequency, the CEO frequency locking device 320 is not required.

[0054] In some embodiments, the CEO frequency locking device 320 may include a phase-locked loop circuit 317 and an acousto-optic modulator (AOM) 302. The phase-locked loop circuit 317 can be connected between the APD 316 and the AOM 302. The circuit can be used for the connection between the phase-locked loop circuit 317 and the APD 316 and the AOM 302 and serves as a signal line. Figure 3 The circuit in is represented by a solid line.

[0055] The phase-locked loop circuit 317 can be used to calculate the frequency error signal of the CEO frequency of the femtosecond laser measured by the CEO frequency measurement device 350 relative to the reference frequency. For example, the phase-locked loop circuit 317 can receive the signal of the CEO frequency measured by the APD 316 from the APD 316, calculate its frequency error signal with the reference frequency, and transmit the frequency error signal to the AOM 302.

[0056] The AOM 302 can be arranged on the optical path between the pump source 301 and the oscillator 303,Figure 3 The optical path through which the pump laser output by the mid-pump source 301 enters the oscillator 303 is indicated by a dotted line. The AOM 302 can be set, for example, between Figure 1 the pump source 101 and the first mirror 102 as shown. The AOM 302 receives the frequency error signal output by the phase-locked loop circuit 317, modulates the power of the pump laser, adjusts the CEO frequency, and thus locks the CEO frequency.

[0057] Figure 4 The accurately dispersion-compensated laser spectrum obtained by the laser of the exemplary embodiment is shown. In the laser of the exemplary embodiment, a pair of chirped mirrors 115 and 116 and a pair of wedges 117 and 118 are introduced outside the cavity of the oscillator 303 to pre-compensate for dispersion. Then, in the CEO frequency measurement device 350, the difference frequency and self-phase modulation incident on the PPLN 311 are focused, and the laser passing through the filter 313 is measured to obtain Figure 4 the spectrum shown.

[0058] As Figure 4 shown, the horizontal axis is the wavelength in nanometers; the left vertical axis is the intensity shown by the dotted line in the figure, and a.u. represents the non-dimensional normalized intensity; the right vertical axis is the absolute intensity obtained by taking the logarithm of the dotted line shown by the solid line in the figure, in decibels. From Figure 4 it can be found that the spectrum is broadened to 1.7 μm. Since the spectrum is expanded to 1600 - 1700 nm, the carrier-envelope phase (CEP) can be measured.

[0059] Figure 5 The beat frequency signal obtained by the laser of the exemplary embodiment is shown. As Figure 5 shown, the horizontal axis is the frequency in megahertz; the vertical axis is the absolute intensity of the beat frequency signal in decibels. Figure 5 What is shown is the measurement result of the APD 316, where f r is the repetition frequency, and f CEO is the CEO frequency measured at the APD 316. As Figure 5 shown, f CEO can be locked near 20 MHz. Since, as Figure 4 shown, the spectrum is expanded to 1600 - 1700 nm, thus, as Figure 5 shown, the intensity of the beat frequency signal at f CEO is as high as 42 dB compared to the noise. Thus, in the laser of the exemplary embodiment, the 1.7 μm band spectrum generated by difference frequency and the spectrum obtained by broadening the self-phase modulation spectrum to the 1.7 μm band are beat at the PPLN 311, and a beat frequency signal with a signal-to-noise ratio greater than 40 dB is measured at the APD 316.

[0060] Figure 6 shows the measurement results of the locking accuracy of the carrier-envelope phase locked by the laser of the exemplary embodiment. As Figure 6 shown, the horizontal axis is the frequency in hertz; the left vertical axis is the power spectral intensity shown by the solid line in the figure, in square radians per hertz; the right vertical axis is the integrated phase noise obtained by integrating the solid line from right to left shown by the dashed line in the figure, in milliradians. Measuring the CEP of the signal output by the APD 316 gives Figure 6 the results shown. As Figure 6 shown, the highest point of the dashed line is 52 mrad, indicating that after the f of the laser of the exemplary embodiment is CEO locked, the noise deviating from the lock is low, achieving high-precision locking. In this case, the requirements for the hardware performance of the phase-locked loop circuit 317 do not have to be stringent.

[0061] In the laser of the exemplary embodiment, a fiber frequency-doubled pump source is adopted to achieve pumping at a wavelength of 515 nm. Compared with the commonly used 532 nm pump source, it is closer to the absorption peak of the titanium sapphire crystal, further improving the optical-optical conversion efficiency and being beneficial to the improvement of the output power. In addition, the laser of the exemplary embodiment can achieve an M-type spectrum with an average power greater than 300 mW, an output bandwidth of 630 - 980 nm, and an ultrashort laser pulse with a pulse width of 6.2 fs. This femtosecond laser can become an ideal tool for experiments on many ultrafast phenomena such as ultrafast spectroscopy, two-photon imaging, and ultrafast pump-probe dynamics.

[0062] The basic principles of the present disclosure have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, advantages, effects, etc. mentioned in the present disclosure are only examples and not limitations, and it cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present disclosure. In addition, the above-disclosed specific details are only for the purposes of illustration and easy understanding, rather than limitations, and the above details do not limit the present disclosure to necessarily adopt the above specific details to implement.

[0063] The block diagrams of the devices, apparatuses, equipment, and systems involved in this disclosure are only illustrative examples and are not intended to require or imply that the connection, arrangement, and configuration must be carried out in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any way. Each block shown in the figures can be subdivided into multiple sub-blocks, and each sub-block can implement the relevant functions or steps, so that multiple sub-blocks can achieve the functions achieved by a large block before subdivision. Alternatively, multiple blocks shown in the figures can also be combined into one block, which can achieve the functions of multiple blocks before combination. In this disclosure, words such as "including", "comprising", "having", etc. are open-ended terms, meaning "including but not limited to", and can be used interchangeably with each other. The words "or" and "and" used here refer to the word "and / or", and can be used interchangeably with it, unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to", and can be used interchangeably with it.

[0064] It should be noted that in the devices, equipment, and methods of this disclosure, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent solutions of this disclosure.

[0065] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects are very obvious to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

[0066] The above description has been given for purposes of illustration and description. In addition, this description is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions, and sub-combinations thereof.

Claims

1. A laser comprising: A pump source, used to generate pump laser; An oscillator, used to output femtosecond laser under the stimulation of the pump laser; as well as A carrier envelope phase offset frequency measuring device is used to measure the carrier envelope phase offset frequency of the femtosecond laser. Wherein, the pump source is an optical fiber frequency doubling pump source.

2. The laser according to claim 1, further comprising a carrier envelope phase offset frequency locking device for locking the carrier envelope phase offset frequency, wherein the carrier envelope phase offset frequency locking device comprises: A phase-locked loop circuit, used for calculating a frequency error signal of the carrier-envelope phase offset frequency of the femtosecond laser measured by the carrier-envelope phase offset frequency measuring device relative to a reference frequency; as well as The acousto-optic modulator is located in the optical path between the pump source and the oscillator, receives the frequency error signal output by the phase-locked loop circuit, and adjusts the carrier envelope phase offset frequency by modulating the power of the pump laser.

3. The laser according to claim 1, wherein: The carrier-envelope phase offset frequency measurement device is a self-difference frequency 0-f module. The pulse width of the femtosecond laser input from the oscillator is less than 10 femtoseconds. The femtosecond laser with a pulse width less than 10 femtoseconds is subjected to self-phase modulation, difference frequency, and spectrum broadening, and the spectrum after broadening is beat to generate a beat frequency signal. The carrier-envelope phase offset frequency is the frequency of the beat frequency signal.

4. The laser according to any one of claims 1 to 3, wherein: The pump source is a sub-10 femtosecond titanium sapphire pump source, the wavelength of the generated pump laser is 515 nanometers, and the pump laser is a single-mode output.

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