Single-crystal dual-procedure parametric laser wavelength converter

Abstract

A single-crystal dual-procedure parametric laser wavelength converter (100a), comprising a pump laser source (110), a nonlinear optical material (122), a first optical reflecting member (150) and a second optical reflecting member (160), wherein the pump laser source (110) emits pump laser pulses (112); the nonlinear optical material (122) receives the pump laser pulses (112), and generates signal laser pulses (134) and some consumed pump laser pulses (114) by means of optical-parametric-amplification; the first optical reflecting member (150) is configured to reflect the signal laser pulses (134) back to the nonlinear optical material (122); and the second optical reflecting member (160) is configured to reflect some of the consumed pump laser pulses (114) back to the nonlinear optical material (122). By means of appropriately adjusting the length of a reflection path, the nonlinear optical material (122) is configured to receive signal laser pulses (134) and some consumed pump laser pulses (114) which are synchronized in terms of time sequence, and to generate an idler-frequency output (115) by means of difference-frequency generation. Both the optical-parametric-amplification and the difference-frequency generation occur in the same nonlinear optical material (122).

Description

Single-crystal dual-process parameter laser wavelength converter Technical Field

[0001] The present invention relates to a laser source, and in particular to a single crystal dual-process parameter laser wavelength converter. Background Art

[0002] There are several methods for generating high-power lasers through laser mixing in nonlinear optical materials. For example, second-order optical parametric wavelength conversion uses a laser to pump a nonlinear optical material to generate two other lasers, called a signal laser and an idler laser. If a pump laser and a strong signal laser are injected into the nonlinear optical material simultaneously, a high-power idler laser can be generated through a process called difference frequency generation. Conservation of photon energy requires that the sum of the signal laser frequency and the idler laser frequency equal the pump laser frequency, while conservation of photon momentum requires that the sum of the signal laser wave vector and the idler laser wave vector equal the pump laser wave vector. The three wave vectors do not need to be collinear.

[0003] Referring to Figure 1, the related art typically employs multiple pump lasers and multiple materials to convert a high-power downconversion output. In this approach, a strong pump laser pulse and a weak continuous-wave signal seed are first converged into a first nonlinear optical material, generating an amplified signal laser pulse through a process known as optical-parametric-amplification (OPA). Subsequently, the newly generated strong signal laser pulse and a new pump laser pulse are injected into a second nonlinear optical material for difference-frequency generation (DFG) to generate an idler laser whose frequency is the difference between the pump and signal laser pulses. To obtain a narrow-spectral idler laser output from the DFG process, a single-frequency pump and a narrow-spectral signal seed are typically used in the DFG process to generate a strong, narrow-spectral signal for the subsequent DFG process. In multiple material solutions in the related art, two expensive pump laser pulses are used for two expensive nonlinear optical materials. Multi-order laser wavelength conversion typically requires rigorous laser calibration. Once the DFG and PFG processes are complete, the two high-power pump laser pulses are discarded and wasted.

[0004] Please refer to Figure 2. In the high-gain state, the pulsed parametric amplification process consumes the frequency center of the pump laser pulse due to the exponential gain in the process, thereby forming a hump at the leading and trailing edges of the pulse where the pump is partially consumed. However, most of the laser energy in the two humps is unused and still very strong, especially when the signal or idler pulse is temporally distant from the pump laser pulse due to material dispersion and non-collinear wave vector matching during the parametric amplification process, so that the partially consumed pump laser pulse penetrates the nonlinear optical material, and the unused humps are still retained. Therefore, the purpose of the present invention includes reflecting the unused hump portion of the pump laser pulse after penetrating the nonlinear optical material back to the original nonlinear optical material for reuse, and further performing a difference frequency generation process with the reflected signal laser pulse to efficiently generate high-power idler pulses.

[0005] Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of related-art parametric laser sources, including the use of multiple materials, waste of pump laser energy, and stringent laser alignment within complex, multi-stage structures. Specifically, the present invention relates to parametric laser wavelength converters that reuse, recycle, and regenerate their pump laser pulses within a single nonlinear optical material to achieve efficient laser wavelength conversion.

[0007] One embodiment of the present invention provides a parametric laser wavelength converter, comprising a pump laser source, a nonlinear optical material, a first optical reflector, and a second optical reflector. The pump laser source is configured to emit pump laser pulses of a first frequency. The nonlinear optical material is configured to receive the pump laser pulses and generate signal laser pulses of a second frequency and partially consumed pump laser pulses through an optical parametric amplification process. The first optical reflector is disposed on the path of the amplified signal laser pulses and is used to reflect the signal laser pulses back to the same nonlinear optical material. The second optical reflector is disposed on the path of the partially consumed pump laser pulses and is used to reflect the partially consumed pump laser pulses back to the same nonlinear optical material. The nonlinear optical material is reused to receive the reflected signal laser pulses and partially consumed pump laser pulses, generating an idler laser output of a third frequency through a difference frequency generation process. The laser frequency of the idler laser output, or the third frequency, is equal to the frequency difference between the first and second frequencies.

[0008] In a parametric laser wavelength converter according to an embodiment of the present invention, partially consumed pump laser pulses generated by the optical parametric amplification process are redirected back to the nonlinear optical material to perform the difference frequency generation process, thereby generating strong idler laser pulses. Therefore, both the optical parametric amplification process and the difference frequency generation process occur within the same nonlinear optical material, eliminating the need for a second nonlinear optical material for the difference frequency generation process, as in related art. This reduces the cost of the parametric laser wavelength converter. Furthermore, the structure of the single-order parametric laser wavelength converter of the present invention alleviates the critical laser calibration often required for multi-order wavelength conversion in related art.

[0009] Another embodiment of the present invention is to adjust the relative paths of the reflected partially consumed pump laser pulse and the reflected signal laser pulse so that the unused hump portion of the partially consumed pump laser pulse overlaps with the peak of the reflected signal laser pulse in the same nonlinear optical material to achieve an efficient difference frequency generation process.

[0010] Another embodiment of the present invention is to first amplify the partially consumed pump laser pulse and then reflect it back to the same nonlinear optical material to perform a difference frequency generation process with the reflected signal laser pulse.

[0011] In order to make the present invention more clear and understandable, some embodiments are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention.

[0013] FIG1 is a schematic structural diagram of a multi-order parameter laser wavelength converter 100 in the related art;

[0014] Figure 2 depicts the temporal pulse profiles of the pump and signal lasers during high-gain parametric amplification;

[0015] FIG3 is a schematic structural diagram of a parametric laser wavelength converter 100a according to an embodiment of the present invention;

[0016] FIG4 is a schematic structural diagram of a parametric laser wavelength converter 100 b according to another embodiment of the present invention;

[0017] FIG5 is a schematic structural diagram of a parametric laser wavelength converter 100c according to another embodiment of the present invention;

[0018] FIG6 is a schematic structural diagram of a parametric laser wavelength converter 100d according to another embodiment of the present invention.

[0019] Explanation of Figure Numbers

[0020] 100:Multi-order parameter laser wavelength converter

[0021] 100a, 100b, 100c, 100d: Parametric laser wavelength converters

[0022] 110: First pump laser source

[0023] 112: Pump laser pulse

[0024] 112d: Part 1

[0025] 114: Partial consumption of pump laser pulses

[0026] 115: Idle laser output

[0027] 120: First nonlinear optical material

[0028] 122: Nonlinear Optical Materials

[0029] 130:Seed laser source

[0030] 132:Seed Laser

[0031] 134:Signal laser pulse

[0032] 140: Second pump laser source

[0033] 142: Second pump laser pulse

[0034] 142d: Part 2

[0035] 150: first optical reflector

[0036] 152: Grating

[0037] 154: Optical reflector

[0038] 156: Aperture

[0039] 160, 160d: second optical reflector

[0040] 170: Optical Splitter

[0041] 172: Optical reflector

[0042] 180: Laser Amplifier

[0043] 200: Depression

[0044] 210, 220: hump

[0045] k p :Pump wave vector

[0046] k s :Signal wave vector

[0047] k i :Idler wave vector

[0048] v s 、v p :Group velocity

[0049] θ: angle DETAILED DESCRIPTION

[0050] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals are used in the drawings and the description to refer to the same or like parts.

[0051] FIG1 is a schematic diagram of the structure of a multi-order parameter laser wavelength converter 100 in the related art. It includes a first pump laser source 110, a second pump laser source 140, a seed laser source 130, a first nonlinear optical material 120, and a second nonlinear optical material 122. p The pump laser (ie, the pump laser pulse 112) is used to pump the nonlinear optical material 120, and a second frequency ω is generated simultaneously through the optical parameter generation process. s The signal laser (ie, the signal laser pulse 134) and the third frequency ω i The idler laser (i.e., idler laser output 115). The three frequency relationships satisfy: ω p =ω s +ω i By injecting a strong pump laser (i.e., pump laser pulse 112) and a weak signal seed (i.e., seed laser 132) into the first nonlinear optical material 120, the weak signal seed 132 can be amplified into a strong signal laser (i.e., signal laser pulse 134) through an optical parameter amplification process. The wave vector matching diagram shows that the pump laser wave vector is the sum of the signal laser wave vector and the idler laser wave vector, i.e., k p =k s +k i , where k is the wave vector, θ is the angle between the pump laser pulse 112 and the signal laser pulse 134 in the first nonlinear optical material 120, and the subscripts p, s, and i represent the pump wave, signal wave, and idler wave, respectively, or the pump laser pulse 112, signal laser pulse 134, and idler laser pulse 115 in Figure 3, respectively. When θ is not equal to 0, all waves propagate in different directions, and the phase condition satisfied by this parametric wavelength conversion process is called non-collinear phase matching. When θ is equal to 0, all waves propagate in the same direction, and the phase condition satisfied by this parametric wavelength conversion process is called collinear phase matching.

[0052] When the power of the mixed pump laser and signal laser is comparable, the optical parametric amplification process, also known as difference frequency generation, occurs. When the pump laser intensity equals the signal laser intensity, the idler laser output is at its highest. In related art, a first pump laser source 110 generates a first pump laser pulse 112, and a seed laser source 130 generates a signal seed 132. The first pump laser pulse 112 and the signal seed 132 are injected into a first nonlinear optical material 120, generating a signal laser pulse 134 and a partially consumed pump laser pulse 114 through the optical parametric amplification process. A second pump laser source 140 generates a second pump laser pulse 142, which is injected into the second nonlinear optical material 122 that receives the signal laser pulse 134. The second pump laser source 140 is then synchronized with the first pump laser source 110 in terms of timing. In the non-collinear wave vector matching process shown, a slant edge is cut out of the nonlinear optical material 122 to receive the mixed second pump laser 142 and the signal laser 134, and an idler laser output 115 is emitted along the normal line on the slant edge.

[0053] FIG2 depicts the timing distribution of the pump laser pulse 112, the signal laser pulse 134, and the partially consumed pump laser pulse 114 during high-gain parametric amplification. Due to the significant exponential gain in the pulse parametric amplification process, the partially consumed pump laser pulse 114 will produce a depression 200 near the pulse center at the output end of the optical parametric amplification process, thereby forming humps 210 and 220 before and after the pulse center. During the optical parametric amplification (OPA) process, the energy of the signal laser pulse 134 is converted from the depression 200 of the pump laser pulse, and its pulse width is usually shorter than that of the pump laser. The laser characteristics of the two humps 210 and 220 are unused and still maintain relatively high power. The time delay between the pump laser pulse 112 and the signal laser pulse 134 is given by the following formula: Δt s，p =d×[cos(θ) / v s -1 / v p], where d is the propagation distance in the nonlinear optical material and v is the group velocity of the laser pulse. When Δt is greater than zero, the pump laser pulse 112 moves faster than the signal laser pulse 134 in the nonlinear optical material 120, resulting in strong consumption at the trailing edge of the partially consumed pump laser pulse 114. Therefore, the reflected signal laser pulse 134 should be aligned with the hump 210 at the leading edge of the reflected partially consumed pump laser pulse 114 to perform the subsequent difference frequency generation process. On the other hand, when Δt is less than zero, the reflected signal laser pulse 134 should be aligned with the hump 220 at the trailing edge of the reflected partially consumed pump laser pulse 114 to perform the subsequent difference frequency generation process. In order to effectively generate the idler laser output 115 in the difference frequency generation process, this embodiment of the present invention discloses a technology of first performing a pulsed light parametric amplification process and reflecting both the pump laser pulse and the signal laser pulse back to the same nonlinear optical material for the difference frequency generation process. However, in the nonlinear optical material 122, the shortened signal laser pulse 134 overlaps with one of the two humps of the partially depleted pump laser pulse 114 to produce a high-power idler laser output 115. Precise timing overlap between the pulses can be achieved by adjusting the position of the optical reflectors of the partially depleted pump laser pulse 114 or the signal laser pulse 134 to achieve timing synchronization of the reflected partially depleted pump laser pulse 114 and the signal laser pulse 134.

[0054] FIG3 is a schematic structural diagram of a parametric laser wavelength converter according to an embodiment of the present invention. The parametric laser wavelength converter 100a in this embodiment includes a pump laser source 110, a nonlinear optical material 122, a first optical reflector 150, and a second optical reflector 160. The pump laser source 110 is configured to emit pump laser pulses 112 of a first frequency. The nonlinear optical material 122 is disposed in the path of the pump laser pulses 112, is configured to receive the pump laser pulses 112, and generates signal laser pulses 134 and partially consumes the pump laser pulses 114 through optical parametric generation. In this embodiment, the parametric laser wavelength converter 100a also includes a seed laser source 130 for emitting a seed laser 132. The nonlinear optical material 122 is configured to receive the pump laser pulses 112 and the seed laser 132, and generates signal laser pulses 134 and partially consumes the pump laser pulses 114 through an optical parametric amplification process. In this embodiment, the pump laser pulses 112 are, for example, single-frequency lasers, while the seed laser 132 are, for example, narrow spectral line continuous wave signals. In this embodiment, a seed laser source 130 is configured to provide seed laser light for amplifying signal pulses during optical parametric amplification. For example, seed laser source 130 is a narrow-line continuous-wave laser source. Furthermore, pump laser pulses 112 and seed laser light 132 are injected into nonlinear optical material 122 together, generating amplified narrow-line signal laser pulses 134 and partially consuming pump laser pulses 114 through the optical parametric amplification process.

[0055] A first optical reflector 150 is disposed in the path of the signal laser pulse 134 and is configured to reflect the signal laser pulse 134 back to the nonlinear optical material 122. A second optical reflector 160 is disposed in the path of the partially depleted pump laser pulse 114 and is configured to reflect the partially depleted pump laser pulse 114 back to the same nonlinear optical material 122. The nonlinear optical material 122 is configured to receive the signal laser pulse 134 and the partially depleted pump laser pulse 114 and generate an idler laser output 115 at a third frequency via a difference frequency generation process. The third frequency is equal to the frequency difference between the first frequency and the second frequency. In this embodiment, the first optical reflector 150 and the second optical reflector 160 are, for example, reflectors.

[0056] In the parametric laser wavelength converter 100a of this embodiment, the partially depleted pump laser pulse 114 generated by the optical parametric amplification process is redirected and reflected back into the nonlinear optical material 122 to perform a difference frequency generation process with the signal laser pulse 134, thereby generating a high-power idler laser output 115. Therefore, the optical parametric amplification and difference frequency generation processes occur within the same nonlinear optical material 122, eliminating the need for a separate nonlinear optical material for difference frequency generation as in related art. This reduces the cost of the parametric laser wavelength converter and simplifies the structure of the parametric laser wavelength converter 100a.

[0057] In this embodiment, the optical path length between the nonlinear optical material 122 and the first optical reflector 150 can be adjusted to be different from the optical path length between the nonlinear optical material 122 and the second optical reflector 160, so that when the partially consumed pump laser pulse 114 reflected by the second optical reflector 160 and the signal laser pulse 134 reflected by the first optical reflector 150 re-enter the nonlinear optical material 122, the unused hump of the partially consumed pump laser pulse 114 can overlap with the signal laser pulse 134.

[0058] Specifically, in this embodiment, pump laser pulses (i.e., initial pump laser pulse 112 and partially depleted pump laser pulse 114) are applied to a single nonlinear optical material 120 to perform optical parametric amplification and difference frequency generation, respectively. In one embodiment, nonlinear optical material 122 has a second-order nonlinear coefficient.

[0059] FIG4 is a schematic diagram of the structure of a parametric laser wavelength converter according to another embodiment of the present invention. Referring to FIG4 , parametric laser wavelength converter 100b in this embodiment is similar to parametric laser wavelength converter 100a in FIG3 , with the following key differences: Parametric laser wavelength converter 100b in this embodiment does not utilize the seed laser source 130 shown in FIG1 . Instead, signal pulses are generated by amplifying vacuum noise with a strong pump pulse in a nonlinear optical material. Consequently, the generated signal pulses are relatively broadband. To limit the signal bandwidth and generate a narrowband idler signal, in this embodiment, a first optical reflector includes a grating 152 and an optical reflector 154. Parametric laser wavelength converter 100b also includes an aperture 156 disposed between grating 152 and nonlinear optical material 122 to allow signal laser pulses 134 of a specific wavelength and bandwidth to pass through. After passing through aperture 156, signal laser pulses 134 have a narrow spectral linewidth for use in the subsequent difference frequency generation process.

[0060] FIG5 is a schematic diagram of the structure of a parametric laser wavelength converter according to another embodiment of the present invention. Referring to FIG5 , the converter further includes a laser amplifier 180. Laser amplifier 180 is disposed in the path of partially consuming pump laser pulses 114. In this embodiment, laser amplifier 180 is a laser gain module. For example, if the pump laser wavelength is 1064 nanometers (nm), it is an optically pumped neodymium-doped yttrium aluminum garnet (Nd:YAG) module. In one embodiment, laser amplifier 180 includes a laser gain material selected from Nd:YAG, neodymium-doped yttrium orthovanadate (Nd:YVO4), neodymium-doped yttrium lithium fluoride (Nd:YLF), and ytterbium-doped yttrium aluminum garnet (Yb:YAG). Laser amplifier 180 is used to boost the energy of the partially depleted pump laser pulse 114 that re-enters the nonlinear optical material 122, further increasing the power of the idler laser output 115 via the difference frequency generation process. The laser gain of laser amplifier 180 can replenish the energy of the partially depleted pump pulse 114, even filling the center dip of the pulse, making subsequent difference frequency generation easier for pulse synchronization.

[0061] Figure 6 is a schematic diagram of the structure of a parametric laser wavelength converter according to another embodiment of the present invention. Referring to Figure 6, parametric laser wavelength converter 100d in this embodiment is similar to parametric laser wavelength converter 100a in Figure 3, with the following key differences. In this embodiment, a pump laser pulse 112 is first split into two parts by an optical splitter 170. The first part 112d is used for optical parametric amplification, while the second part 142d and the reflected signal laser pulse are used for the subsequent difference frequency generation process. The optical parametric amplification and difference frequency generation processes are performed within the same nonlinear optical material 122. An optical reflector 172 is used to reflect the second part 142d toward a second optical reflector 160d. In this embodiment, the initial pump pulse is generated by a high-power laser source with sufficient energy to perform both the optical parametric amplification and difference frequency generation processes. An advantage of this embodiment is that, without a depletion notch in the second pump pulse, pulse synchronization for the difference frequency generation process is facilitated.

[0062] In summary, in the parametric laser wavelength converter of the embodiment of the present invention, part of the depletion pump laser pulses generated by the optical parametric process are reset back to the nonlinear optical material to perform the difference frequency generation process, thereby generating a high-power idler output. Therefore, the optical parametric amplification process and the difference frequency generation process occur in the same nonlinear optical material, without the need for another nonlinear optical material for the difference frequency generation process as in the related art. The cost of the parametric laser wavelength converter of the present invention is reduced, and the structure of the parametric laser wavelength converter is simplified.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parametric laser wavelength converter for generating laser radiation, characterized in that include: A pump laser source for emitting a pump laser pulse having a first frequency; A nonlinear optical material, for receiving the pump laser pulse and generating a signal laser pulse having a second frequency and a partially consumed pump pulse through an optical parameter amplification process; A first optical reflector, used for reflecting the signal laser pulse back to the nonlinear optical material; as well as A second optical reflector is used to reflect the partially consumed pump pulse back to the nonlinear optical material for use in a difference frequency generation process, wherein the nonlinear optical material is used to receive the signal laser pulse and the partially consumed pump pulse to generate an idler laser output, wherein the frequency of the idler laser is equal to the frequency difference between the first frequency and the second frequency.

2. The parametric laser wavelength converter according to claim 1, characterized in that: The nonlinear optical material has a second-order nonlinear coefficient.

3. The parametric laser wavelength converter according to claim 1, characterized in that: The optical path length between the nonlinear optical material and the first optical reflector is different from the optical path length between the nonlinear optical material and the second optical reflector, so that when the partially consumed pump laser pulse reflected by the second optical reflector and the signal laser pulse reflected by the first optical reflector re-enter the nonlinear optical material, the unused hump of the partially consumed pump laser pulse overlaps with the signal laser pulse.

4. The parametric laser wavelength converter according to claim 1, characterized in that: It also includes a seed laser source for providing a seed laser for amplifying signal pulses in the parameter amplification process.

5. The parametric laser wavelength converter according to claim 4, characterized in that: The seed laser source is a narrow spectrum line continuous wave laser source.

6. The parametric laser wavelength converter according to claim 1, characterized in that: The first light reflecting member further comprises a grating, an optical reflector, and an aperture disposed between the grating and the nonlinear optical material to allow the signal laser pulse with a specific wavelength and bandwidth to pass through.

7. The parametric laser wavelength converter according to claim 1, characterized in that: Also included is a laser amplifier for enhancing the energy of the partially consumed pump laser pulse that re-enters the nonlinear optical material.

8. The parametric laser wavelength converter according to claim 7, characterized in that: The laser amplifier includes a laser gain material selected from one of Nd:YAG, Nd:YVO4, Nd:YLF and Yb:YAG.

9. The parametric laser wavelength converter according to claim 1, characterized in that: The pump laser pulse is divided into two pulses, the first pulse is used to perform an optical parameter generation process, and the second pulse is used to perform a subsequent difference frequency generation process in the same nonlinear optical material.

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